EVALUATION OF SUPERCIRTICAL FLUID CHROMATOGRAPHY COUPLED TO TANDEM MASS SPECTROMETRY FOR PESTICIDE RESIDUES IN FOOD J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-23 Víctor Cutillas, María Martínez Galera, Łukasz Rajski, Amadeo R. Fernández-Alba
Supercritical fluid chromatography coupled to triple quadrupole mass spectrometry has been evaluated for pesticide residues in food. In order to check its advantages and limitations it was developed a method to identify and quantify 164 pesticides in three different matrices (tomato, orange and leek). A carbon dioxide gradient with methanol (containing 1 mM ammonium formate) was used allowing a flow rate of 1.5 mL/min that made the total run time of 12 min without any problem of overpressure. Addition of a post column flow 150 μL/min of Methanol with ammonium formate/formic acid was necessary to improve the ionization.The matrix effect study revealed that the percentages of pesticides with irrelevant matrix effect (suppression lower than 20%) was 99% in tomato, 87% in orange and 62% in leek, whereas significant suppression (higher than 50%) was not found in tomato and only 1% of the compounds in orange and 3% in leek.These results compare favorably with that typically obtained in LC-MS/MS. The absence of water in the mobile phase, also provided some important advantages regarding LC-MS/MS as (i) higher retention of polar compounds in the column, which elute with high sensitivity and good peak shape and (ii) a general increase of the sensitivity of the analysis, consequence of the high ionization and ion extraction efficiency.Pesticides evaluated were identified following the SANTE/11813/2017. At the spiking concentration of 5 μg/kg, 98% of the pesticides were identified in tomato, 98% in orange and 94% in leek, whereas for the concentration of 10 μg/kg all the compounds were identified in tomato and only spiromesifen was not identified in orange and leek. At the concentration of 20 μg/kg, spiromesifen was also identified in these two matrices. The linearity and reproducibility of the method were evaluated with results which guarantee high quality in the analytical measurements. Even though only 2 μL of final extract were injected, the sensitivity of the SFC method was enough to achieve stringent LOQs.Real samples, including 6 different fruits and vegetables, were analyzed by the SFC-MS/MS proposed method, the results being similar to those obtained by LC-MS/MS. The method was also applied to a proficiency test of fipronil in eggs with good results in all the cases.Carbon dioxide as mobile phase with methanol as modifier can represent a good alternative to LC-MS/MS with reduction of matrix effects and shorter run times.
A miniaturized sorbent phase-based extraction device in the form of syringe filter holder using molecularly imprinted polymer as sorbent and its application to extract benzophenones J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-22 Xiao Sun, Xin-yue Jiao, Jing Li, Li Xu
The molecularly imprinted polymer using 2,4-dihydroxybenzophenone as the template (DHBP-MIP) was synthesized via sacrificial support method. The DHBP-MIP was demonstrated to possess good adsorption capacity and selectivity towards benzophenones. Moreover, a miniaturized sorbent phase-based extraction device in the form of syringe filter holder using DHBP-MIP as the sorbent was proposed, and named as μ-SPE-SFH-MIP device. The μ-SPE-SFH-MIP device consisted of a reusable syringe filter holder, flexible amount of sorbent and a sub-microporous membrane, which could be conveniently connected to different driving forces, like syringe pump, solid-phase extraction device and peristaltic pump. It was successfully applied to extract five benzophenones from swimming pool water and human urine samples, combined with high performance liquid chromatograph-UV analysis, with detection limits of 0.12-0.68 μg L−1 and 0.21-1.05 μg L−1, respectively. The accuracy and precision of the analytes were in the range of 89.27%-113.35% for swimming pool water samples and 90.65%-108.00% for urine samples, with all the relative standard deviation values below 7.89%. The μ-SPE-SFH-MIP device was portable, cost-effective operational convenient and suitable for the small-size samples; moreover, with the MIP as the sorbent, it afforded additional high selectivity and sensitivity.
Zeolitic imidazolate framework-8 for selective extraction of a highly active anti-oxidant flavonoid from Caragana Jubata J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-22 Yuan-Yuan Cui, Cheng-Xiong Yang, Xue-Dong Yang, Xiu-Ping Yan
The medicinal compositions or active components in medicinal plants are the major sources to find new drugs or lead compounds. Exploring novel sorbents with good selectivity for extraction and separation of medicinal compositions or active components from complex medicinal plants are interesting and challenging. Metal-organic frameworks (MOFs) show great potential in adsorption and extraction recently. Herein, we report our primary attempt of zeolitic imidazolate framework-8 (ZIF-8) as a model MOF for selective extraction of a flavonoid named 3,4-dihydroxy-8,9-methylenedioxypterocarpan (compound 1) from a traditional medicinal plant Caragana Jubata. The enrichment factor of ZIF-8 for compound 1 is 57.7. The recoveries of compound 1 at three spiked levels (50, 100, 150 mg L−1) in Caragana Jubata dichloromethane extract are 62.1%, 66.4%, and 75.4%, respectively, with the relative standard deviations of less than 2.9%. The compound 1 also gave good linearity (R2 of 0.999) in the concentration range of 5–1000 mg L−1. The obtained compound 1 gave highly antioxidant activity (DPPH radical scavenging rate of 79.03%, inhibitory rate on lipid peroxidation of 75.30%, which were higher than the positive controls Vitamin C and BHT) and low IC50 values (5.438 ± 0.068, 20.970 ± 0.083 μg mL−1 for DPPH radical scavenging activities and inhibitory effects on lipid peroxidation, respectively). These results demonstrated the feasibility of MOFs in selective extraction of medicinal compositions or active components from complex medicinal plants. The current work may open a new way of MOFs in selective extraction of pharmacological active components from medicinal plants.
Synthesis of boronate-decorated polyethyleneimine-grafted porous layer open tubular capillaries for enrichment of polyphenols in fruit juices J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Ling-Ling Ying, De-Yin Wang, Hui-Ping Yang, Xi-Yan Deng, Chao Peng, Chao Zheng, Bei Xu, Lin-Yi Dong, Xu Wang, Liang Xu, Yan-Wen Zhang, Xian-Hua Wang
A combination between modification with porous layer and grafting of polyethyleneimine (PEI) on the inner face of capillary was for the first time developed for boronate affinity in-tube solid-phase microextraction (SPME) material to enhance the extraction capacity for cis-diol-containing polyphenols. The successful synthesis of boronate-decorated polyethyleneimine-grafted porous layer open tubular (BPPLOT) capillary was confirmed by scanning electron micrograph, Fourier transform-infrared spectra and absorption experiments. The porous layer, PEI and boronate affinity provided high specific surface area, more binding sites for boronate groups and specific selectivity of BPPLOT capillary, respectively. The maximum binding quantity of BPPLOT capillary greatly improved, and ranged from 143 to 170 μg m−1 for cis-diol-containing polyphenols (catechin, chlorogenic acid, caffeic acid and epicatechin). A green method based on boronate affinity in-tube SPME was developed for separation and enrichment polyphenols, and some parameters of in-tube SPME were optimized. After in-tube SPME, HPLC with UV detection was used for quantitative determination of polyphenols. Recoveries of standard spiked cis-diol-containing polyphenols from fruit juice were between 80.9% and 102%, with intra-day and inter-day coefficient of variation ranging from 4.8% to 7.3% and 5.0% to 8.6%, respectively. Conversely, recovery of non-cis-diol-containing ferulic acid was no greater than 3.0%. These results suggested that the BPPLOT capillary could effectively separate and enrich cis-diol-containing polyphenols from real samples.
Mobile phase effects in Reversed-Phase and Hydrophilic Interaction Liquid Chromatography revisited. J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Pavel Jandera, Tomáš Hájek, Zuzana Šromová
Correct adjustment of the mobile phase is equally important as the selection of the appropriate column for the separation of polar compounds in LC. Both solvophobic and selective polar interactions control the retention in the Reversed Phase and Hydrophilic Interaction modes. The retention models describing the effects of the volume fraction of the strong eluent component in binary mobile phases on the sample retention factors apply in a limited mobile phase composition range. We introduced a three-parameter retention model, which provides improved prediction of retention over a broad mobile phase range, under isocratic and gradient elution conditions. The model does not imply any assumptions concerning either adsorption or partition distribution mechanism, but allows estimating retention in pure strong and in pure weak mobile phase components. The experimental retention data for phenolic acids and flavones on several core-shell columns with different types of stationary phases agree with the theory. Many polar columns with important structural hydrophobic moieties show dual retention mechanism, (Reversed Phase in water rich mobile phases and Hydrophilic Interaction at high acetonitrile concentrations). It is possible to select the mobile phase compositions in each of the two modes for separations of samples containing compounds largely differing in polarity. The three-parameter model describes the retention in each mode, with separately determined best-fit parameters. We applied the two-mode model to the retention data of sulfonamides and benzoic acid related compounds on a new polymethacrylate zwitterionic monolithic micro-column.
New 3D-printed sorbent for extraction of steroids from human plasma preceding LC–MS analysis ☆ J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Lucyna Konieczna, Mariusz Belka, Magdalena Okońska, Magdalena Pyszka, Tomasz Bączek
In recent years, there has been an increasing worldwide interest in the use of alternative sample preparation methods that are proceeded by separation techniques. Fused deposition modeling (FDM) is a 3D printing technique that is based the consecutive layering of softened/melted thermoplastic materials. In this study, a group of natural steroids and sexual hormones – namely, aldosterone, cortisol, β-estradiol, testosterone, dihydrotestosterone, and synthetic methyltestosterone and betamethasone – were separated and determined using an optimized high-performance liquid chromatography coupled to mass spectrometry (LC–MS) method in positive ionization mode. 3D-printed sorbents were selected as the pre-concentration technique because they are generally low cost, fast, and simple to make and automate. Furthermore, the use of 3D-printed sorbents helps to minimize potential errors due to their repeatability and reproducibility, and their ability to eliminate carry over by using one printed sorbent for a single extraction of steroids from biological matrices. The extraction procedure was optimized and the parameters influencing 3D-printed Layfomm 60® based sorbent and LC–MS were studied, including the type of extraction solvent used, sorption and desorption times, temperature, and the salting-out effect. To demonstrate this method’s applicability for biological sample analysis, the SPME-LC–MS method was validated for its ability to simultaneously quantify endogenous steroids. This evaluation confirmed good linearity and an R2 that was between 0.9970 and 0.9990. The recovery rates for human plasma samples were 86.34–93.6% for the studied steroids with intra- and inter-day RSDs of 1.02–7.42% and 1.44–9.46%, respectively. To our knowledge, this study is the first time that 3D-printed sorbents have been used to extract trace amounts of endogenous low-molecular-weight compounds, such as steroids, from biological samples, such as plasma.
On-line solid phase extraction-liquid chromatography-tandem mass spectrometry for insect repellent residue analysis in surface waters using atmospheric pressure photoionization J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Daniel Molins-Delgado, Daniel García-Sillero, M. Silvia Díaz-Cruz, Damià Barceló
Insect repellents (IRs) are a group of organic chemicals whose function is to prevent the ability of insects of landing in a surface. These compounds have been found in the environment and may pose a risk to non-target organisms. In this study, an on-line solid phase extraction − high performance liquid chromatography-tandem mass spectrometry multiresidue method was developed using an atmospheric photoionization source (SPE-HPLC-(APPI)-MS/MS). The use of the APPI as an alternative ionization technique to electrospray (ESI) and atmospheric pressure chemical ionisation (APCI) allowed expanding the range of analytical techniques suitable for the analysis of IRs, so far relied in gas chromatography. High sensitivity and precision was reached with method limits of quantification between 0.2 and 4.6 ng l−1 and interday and intraday precision equal or below 15%. The validated method was applied to the study of surface water samples from three European river basins with different flow regime (Adige River in Italy, Sava River in the Balkans, and Evrotas River in Greece). The results showed that two IRs (DEET and Bayrepel) were ubiquitous in the Sava and Evrotas basins, reaching concentrations as high as 105 μg l−1 of Bayrepel in the Sava River, and 5 μg l−1 of DEET in the Evrotas River. Densely populated areas and effluent wastewaters are pointed out as the responsible for this pollution. In the alpine river Adige, only three samples showed low levels of IRs (6.01-37.8 ng l−1). The concentrations measured were used to perform an environmental risk assessment based on the hazard quotients (HQs) estimation approach by using the chronic and acute eco-toxicity data available. The results revealed that despite the high frequency and eventually high concentrations of these IRs determined in the three basins, only few sites were at risk, with 1 < HQs < 3.3.
Metabolic study of methylstenbolone in horses using liquid chromatography-high resolution mass spectrometry and gas chromatography-mass spectrometry J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Timmy L.S. Choi, Jenny K.Y. Wong, Wai Him Kwok, Peter Curl, Stewart Mechie, Terence S.M. Wan
Methylstenbolone (2,17α-dimethyl-5α-androst-1-en-17β-ol-3-one) is a synthetic anabolic and androgenic steroid (AAS) sold as an oral ‘nutritional supplement’ under the brand names ‘Ultradrol’, ‘M-Sten’ and ‘Methyl-Sten’. Like other AASs, methylstenbolone is a prohibited substance in both human and equine sports. This paper describes the studies of the in vitro and in vivo metabolism of methylstenbolone in horses using LC/HRMS, GC/MS and GC/MS/MS. Phase I in vitro metabolic study of methylstenbolone was performed using homogenised horse liver. Hydroxylation was the only biotransformation observed. Six in vitro metabolites were detected including four mono-hydroxylated metabolites, namely 16α/β-hydroxymethylstenbolone (M1a, M1b), 20-hydroxymethylstenbolone (M1c), 6-hydroxymethylstenbolone (M1d), and two dihydroxylated methylstenbolone metabolites (M2c–M2d). An in vivo experiment was carried out using two retired thoroughbred geldings. Each horse was administered with 100 mg methylstenbolone supplement by stomach tubing daily for three consecutive days. Methylstenbolone and 14 metabolites were detected in the post-administration urine samples. The proposed in vivo metabolites included 16α/β-hydroxymethylstenbolone (M1a, M1b), 20-hydroxymethylstenbolone (M1c), two dihydroxylated methylstenbolone (M2a, M2b), 17-epi-methylstenbolone (M3), methasterone (M4), 2,17-dimethylandrostane-16,17-diol-3-one (M5), dihydroxylated and reduced methylstenbolone (M6), 2α,17α-dimethylandrostane-3α,17β-diol (M7), 2,17-dimethylandrostane-3,16,17-triol (M8a–M8c) and 2,17-dimethylandrostane-2,3,16,17-tetraol (M9), formed from hydroxylation, reduction and epimerisation. The highest concentration of methylstenbolone detected in urine was about 10–36 ng/mL at 3–4 h after the last administration, while the maximum concentration in plasma was about 0.4–0.7 ng/mL at 1 h after the last administration. For controlling the misuse of methylstenbolone, M8c and M9 gave the longest detection time in urine, while M4, M5 and M6 were the longest detecting analytes in plasma. They could be detected for up to 5 and 4.5 days respectively in urine and plasma. Apart from 16α/β-hydroxymethylstenbolone (M1a, M1b), the methylstenbolone metabolites reported herein have never been reported before.
Observation and explanation of two-dimensional interconversion of oximes with multiple heart-cutting using comprehensive multidimensional gas chromatography J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Chadin Kulsing, Yada Nolvachai, Yong Foo Wong, Melissa I. Glouzman, Philip J. Marriott
Real-time interconversion processes produce unconventional peak broadening in gas chromatography (GC), and can be used to generate kinetic and thermodynamic data. In this study, an unusual separation situation in comprehensive two dimensional GC (both GC×GC and GC-GC) where two dimensional interconversion (i.e. a raised plateau in both first and second dimension, 1D and 2D, directions) was observed in analysis of enantio- and stereo-isomers of 2-phenylpropanaldehyde oxime. This resulted in a characteristic and unusual rectangular peak shape in the two dimensional result. A related theoretical approach was introduced to explain the peak shape supported by simulation results which can be varied depending on concentration profiles and kinetics of the process. The simulated results were supported by experimental results obtained by a comprehensive heart-cut multidimensional GC (H/C MDGC) approach which was developed to clearly investigate diastereomerisation of E/Z oxime molecules in both 1D and 2D separations under different isothermal conditions. The carrier gas flow and oven temperature were selected according to initial results for 1D interconversion on a poly(ethyleneglycol) stationary phase, which was further used as both 1D and 2D columns to result in a broad zone of oxime interconversion in both dimensions of separations. The method involved repetitive injections of oxime sample, then sampling contiguous fractions of sample into a long 2D column which is intended to promote considerable interconversion. Comprehensiveness arises from the fact that the whole sample is sampled from the 1D to the 2D column, with the long 2D column replacing the short 2D column used in classical comprehensive two-dimensional gas chromatography, where the latter will not promote sufficient interconversion. Data processing and presentation permits a ‘rectangular’ distribution corresponding to the separated compounds, characteristic of this experiment.
Linear solvation energy relationship (LSER) characterization of the normal phase retention mechanism on hypercrosslinked polystyrenes J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Di Wu, Ping Jiang, Charles A. Lucy
Linear solvation energy relationships (LSERs) were applied to retention on hypercrosslinked polystyrene on silica (HC-Tol) to elucidate the type and relative importance of molecular interactions between model solutes and the HC-Tol stationary phase. Classical amino phase and another hypercrosslinked phase (5-HGN) were used as reference columns. On both the HC-Tol and amino, polar interactions predominate and contribute to retention. Solute volume V has no impact on retention on the amino column, while V has a slightly negative influence on retention for the HC-Tol column. The differences in coefficient v between the amino and the HC-Tol columns might explain why the HC-Tol is capable of group-type separations. 5-HGN phase has smaller a and b values compared to HC-Tol, which means that 5-HGN is not as basic or acidic in terms of hydrogen bonds as is HC-Tol. This suggests that the hydrogen bonding character of the HC-Tol phase arises from its silica substrate.
Discovered acetylcholinesterase inhibition and antibacterial activity of polyacetylenes in tansy root extract via effect-directed chromatographic fingerprints J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Ágnes M. Móricz, Péter G. Ott, Gertrud E. Morlock
The knowledge about the activity of polyacetylenes was extended by their new acetylcholinesterase inhibition and antibacterial activity against plant pathogenic bacteria. For this discovery, an utmost streamlined workflow, which we consider to be of high potential in the field of natural product or superfood search was developed. It demonstrates the combined power of biological, biochemical and chemical fingerprints. Bioactive components of tansy (Tanacetum vulgare L.) root extract were profiled and identified by high-performance thin-layer chromatography hyphenated with in situ effect-directed analysis, chemical derivatizations and high-resolution mass spectrometry (HPTLC-UV/Vis/FLD-EDA-HRMS). The effect-directed profiling was performed using four bacterial bioassays including two plant pathogens, an antioxidant assay and acetyl- and butyrylcholinesterase inhibitory assays. The chromatographic, spectral and powerful mass spectrometric study of zones that exerted substantial antibacterial and/or antioxidant and/or acetylcholinesterase inhibitory effects allowed these multi-potent zones to be identified as polyacetylenes. Five polyacetylene compounds were assigned to be 2-non-1-ene-3,5,7-triynyl-3-vinyl-oxirane, 2-(2,4-hexadiynylidene)-3,4-epoxy-1,6-dioxaspiro[4.5]decane, trans- and cis-2-(2,4-hexadiynylidene)-1,6-dioxaspiro[4.5]dec-3-ene and tetradeca-2,4,6-triine-8-en-12-one. This study clearly showed the advantage of the combined use of different ionization sources, i.e. electrospray ionization via an elution-head based interface and also the Direct Analysis in Real Time interface, for HRMS analysis of compounds from the same class with very similar chromatographic behavior and polarity.
Integration of electropreconcentration and electrospray ionization in a microchip J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Honggu Chun
A microfluidic glass chip for performing sensitive mass spectrometry (MS) is developed by integrating nanochannel-based electropreconcentration with electrospray ionization (ESI). Cation analytes in acidic buffer conditions (∼pH 3) were preconcentrated at a micro-nano-microchannel junction where a positively charged polymer, polyE-323, is coated to reverse the electroosmotic flows (anodic EOF) and prevent sample adsorption. The preconcentrated cation analytes were delivered to a monolithic spray tip using an integrated field-free electrokinetic pump, enabling a stable positive ESI with negligible dead volume. The sample preconcentration-ESI-MS achieved one order of magnitude signal enhancement in MS signal with a peptide mixture.
Ultra-high performance liquid chromatography with fluorescence detection following salting-out assisted liquid–liquid extraction for the analysis of benzimidazole residues in farm fish samples ☆ J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-21 Carmen Tejada-Casado, Francisco J. Lara, Ana M. García-Campaña, Monsalud del Olmo-Iruela
Ultra-high performance liquid chromatography (UHPLC) coupled with fluorescence detection (FL) has been proposed for the first time to determine thirteen benzimidazoles (BZs) in farmed fish samples. In order to optimize the chromatographic separation, parameters such as mobile phase composition and flow rate were carefully studied, establishing a gradient mode with a mobile phase consisted of water (solvent A) and acetonitrile (solvent B) at a flow rate of 0.4 mL/min. The separation was performed on a Zorbax Eclipse Plus RRHD C18 column (50 × 2.1 mm, 1.8 μm), involving a total analysis time lower than 12 min. Salting-out assisted liquid-liquid extraction (SALLE) was applied as sample treatment to different types of farmed fish (trout, sea bream and sea bass). To obtain satisfactory extraction efficiencies for the studied analytes, several parameters affecting the SALLE procedure were optimized including the amount of sample, type and volume of the extraction solvent, and the nature and amount of the salt used. Characterization of the method in terms of performance characteristics was carried out, obtaining satisfactory results for the linearity (R2 ≥ 0.997), repeatability (RSD ≤ 6.1%), reproducibility (RSD ≤ 10.8%) and recoveries (R ≥ 79%; RSD ≤ 7.8%). Detection limits between 0.04 to 29.9 μg kg−1 were obtained, demonstrating the applicability of this fast, simple and environmentally friendly method.
Determination of free formaldehyde in cosmetics containing formaldehyde-releasing preservatives by reversed-phase dispersive liquid-liquid microextraction and liquid chromatography with post-column derivatization ☆ J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-20 Pablo Miralles, Alberto Chisvert, M. José Alonso, Sandra Hernandorena, Amparo Salvador
An analytical method for the determination of traces of formaldehyde in cosmetic products containing formaldehyde-releasing preservatives has been developed. The method is based on reversed-phase dispersive liquid-liquid microextraction (RP-DLLME), that allows the extraction of highly polar compounds, followed by liquid chromatography–ultraviolet/visible (LC–UV/vis) determination with post-column derivatization. The variables involved in the RP-DLLME process were studied to provide the best enrichment factors. Under the selected conditions, a mixture of 500 μL of acetonitrile (disperser solvent) and 50 μL of water (extraction solvent) was rapidly injected into 5 mL of toluene sample solution. The extracts were injected into the LC–UV/vis system using phosphate buffer 6 mmol L−1 at pH 2 as mobile phase. After chromatographic separation, the eluate merged with a flow stream of pentane-2,4-dione in ammonium acetate solution as derivatizing reagent and passed throughout a post-column reactor at 85 °C in order to derivatize formaldehyde into 3,5-diacetyl-1,4-dihydrolutidine, according to Hantzsch reaction, which was finally measured spectrophotometrically at 407 nm. The method was successfully validated showing good linearity, an enrichment factor of 86 ± 2, limits of detection and quantification of 0.7 and 2.3 ng mL−1, respectively, and good repeatability (RSD < 9.2%). Finally, the proposed analytical method was applied to the determination of formaldehyde in different commercial cosmetic samples containing formaldehyde-releasing preservatives, such as bronopol, diazolidinyl urea, imidazolidinyl urea, and DMDM hydantoin, with good relative recovery values (91–113%) thus showing that matrix effects were negligible. The good analytical features of the proposed method besides of its simplicity and affordability, make it useful to carry out the quality control of cosmetic products containing formaldehyde-releasing preservatives.
Cyclodextrin based polymer sorbents for micro-solid phase extraction followed by liquid chromatography tandem mass spectrometry in determination of endogenous steroids J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-20 Normaliza Abdul Manaf, Bahruddin Saad, Mohamed H. Mohamed, Lee D. Wilson, Aishah A. Latiff
Sorbents were prepared by cross-linking β-cyclodextrin (β-CD) using two different types of cross-linker units at variable reactant mole ratios. The resulting polymers containing β-CD were evaluated as sorbents in micro-solid phase extraction (μ-SPE) format for the extraction of the endogenous steroids testosterone (T), epitestosterone (E), androsterone (A), etiocholanolone (Etio), 5α-androstane-3α,17β-diol (5αAdiol) and 5β-androstane-3α,17β-diol (5βAdiol). The best sorbent (C1; cyclodextrin polymer) showed superior extraction characteristics compared with commercial sorbents (C18 and Bond Elut Plexa). Parameters influencing the extraction efficiency of the C1 sorbent such as extraction and desorption times, desorption solvent and volume of sample were investigated. The extracts were separated using a Hypersil Gold column (50 × 2.1 mm, 1.9 μm) under gradient elution coupled to a LC–MS/MS. The compounds were successfully separated within 8 min. The method offers good repeatability (RSD < 10%) and linearity (r2 > 0.995) were within the range of 1–200 ng mL−1 for T and E, 250–4000 ng mL−1 for A and Etio and 25–500 ng mL−1 for 5αAdiol and 5βAdiol, respectively. The method was applied for the determination of steroid profile of urine from volunteers.
Urea functionalized surface-bonded sol-gel coating for on-line hyphenation of capillary microextraction with high-performance liquid chromatography J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-19 Shehzada Muhammad Sajid Jillani, Khalid Alhooshani
Sol-gel urea functionalized-[bis(hydroxyethyl)amine] terminated polydimethylsiloxane coating was developed for capillary microextraction-high performance liquid chromatographic analysis from aqueous samples. A fused silica capillary is coated from the inside with surface bonded coating material and is created through in-situ sol-gel reaction. The urea-functionalized coating was immobilized to the inner surface of the capillary by the condensation reaction of silanol groups of capillary and sol-solution. The characterization of the coating material was successfully done by using X-ray photoelectron spectroscopy, thermogravimetric analysis, field emission scanning electron microscope, and energy dispersive X-ray spectrometer. To make a setup of online capillary microextraction-high performance liquid chromatography, the urea functionalized capillary was installed in the HPLC manual injection port. The analytes of interest were pre-concentrated in the coated sampling loop, desorbed by the mobile phase, chromatographically separated on C-18 column, and analyzed by UV detector. Sol-gel coated capillaries were used for online extraction and high-performance liquid chromatographic analysis of phenols, ketones, aldehydes, and polyaromatic hydrocarbons. This newly developed coating showed excellent extraction for a variety of analytes ranging from highly polar to non-polar in nature. The analysis using sol-gel coating showed excellent overall sensitivity in terms of lower detection limits (S/N = 3) for the analytes (0.10 ng mL−1 to 14.29 ng mL−1) with acceptable reproducibility that is less than 12.0%RSD (n = 3). Moreover, the capillary to capillary reproducibility of the analysis was also tested by changing the capillary of the same size. This provided excellent %RSD of less than 10.0% (n = 3).
Optimization and application of parallel solid-phase extraction coupled with ultra-high performance liquid chromatography-tandem mass spectrometry for the determination of 11 aminoglycoside residues in honey and royal jelly J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-19 Xinran Wang, Shupeng Yang, Yi Li, Jinzhen Zhang, Yue Jin, Wen Zhao, Yongxin Zhang, Jingping Huang, Peng Wang, Cuiling Wu, Jinhui Zhou
A robust and sensitive method of solid-phase extraction followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was established and performed for the simultaneous determination of eleven aminoglycosides (AGs) in royal jelly and honey. After sample extraction by a phosphate buffer containing trichloroacetic acid (TCA) and ethylenediaminetetracetic acid disodium salt (Na2EDTA), the extraction solution was subjected to a parallel solid-phase extraction for clean-up prior to the LC-MS/MS analysis. The same method was applied to analyze two completely different matrices, honey and royal jelly. Good sensitivity, repeatability, and recovery were obtained by using the mobile phase without an ion-pairing reagent such as heptafluorobutyric acid (HFBA) or sodium heptanesulfonate. The calibration curves of the honey and royal jelly samples exhibited a good linear response (R2 > 0.99) at six concentrations in the range of 10–1000 μg/mL. The limit of quantification (LOQ) of the AGs ranged from 10 to 25 μg/kg in the honey and from 12.5 to 25 μg/kg in the royal jelly. The recoveries of the AGs for the honey and royal jelly samples were in the range of 79.48% to 108.95% and 74.61% to 113.70% respectively and the relative standard deviations (RSDs) were between 1.23% and 9.59%, and between 1.51% and 9.98%, respectively. The proposed approach has been allowed in China as a reference method for the simultaneous determination of eleven AGs in honey and royal jelly.
Electrospun UiO-66/polyacrylonitrile nanofibers as efficient sorbent for pipette tip solid phase extraction of phytohormones in vegetable samples J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-19 Zhiming Yan, Mei Wu, Biqing Hu, Minna Yao, Lan Zhang, Qiaomei Lu, Jie Pang
In this work, metal-organic framework particles incorporated fibers (UiO-66/PAN nanofibers) were used as adsorbent in pipette tip solid phase extraction (PT-SPE) for the first time. The UiO-66/PAN nanofibers were fabricated by a facile electrospinning method and characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and nitrogen adsorption-desorption experiments. The UiO-66/PAN nanofibers were applied to assemble a novel PT-SPE cartridge for determination of four phytohormones followed by high performance liquid chromatography (HPLC). Several experimental parameters such as kinds of UiO-66/PAN nanofibers, the amount of UiO-66/PAN nanofibers, the effect of solution pH, ionic strength and desorption conditions were intensively investigated. Under the optimal conditions, the linear ranges of the phytohormones were in the range of 0.06–60 ng/mL with correlation coefficients above 0.992. The limits of detection were between 0.01 ng/mL to 0.02 ng/mL. The interday and intraday precision (RSD) for three replicate extractions of the four phytohormones (15 ng/mL for each) was in the range of 1.5-5.6%. The established method was successfully applied for the determination of phytohormones in watermelon and mung bean sprouts samples. The results showed that the electrostatic interaction between the positively charged UiO-66 and anionic forms of phytohormones played an important role in the extraction of the phytohormones.
Simultaneous determination of trace concentrations of aldehydes and carboxylic acids in particulate matter J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-18 Jana Rousová, Manikyala R. Chintapalli, Anastasia Lindahl, Jana Casey, Alena Kubátová
Carboxylic acids and aldehydes are present in ambient air particulate matter (PM) originating from both primary emission and secondary production in air and may, due to their polarity have, an impact on formation of cloud condensation nuclei. Their simultaneous determination may provide improved understanding of atmospheric processes. We developed a new analytical method allowing for a single step determination of majority of carboxylic acids and aldehydes (+ 95 compounds). This sample preparation employed O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA·HCl) in methanol to yield oximes (for aldehydes) and methyl esters (for majority of acids); with the limits of detection of 0.02–1 ng per injection, corresponding to approximately 0.4–20 μg/gPM. Subsequent trimethylsilylation with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) was employed only for aromatic acids, which were not completely esterified, and for hydroxyl groups. Our method, in contrast to previous primarily qualitative studies, based on derivatization with an aqueous PFBHA followed by BSTFA derivatization, is less labor-intesive and reduces sample losses caused by an evaporation. The method was tested with a broad range of functionalized compounds (95), including monocarboxylic, dicarboxylic and aromatic acids, ketoacids, hydroxyacids and aldehydes. The developed protocol was applied to wood smoke (WS) and urban air standard reference material 1648b (UA) PM. The observed concentrations of aldehydes were 10–3000 μg/gPM in WS PM and 10–900 μg/gPM in UA PM, while those of acids were 20–1800 μg/gPM in WS PM and 15–1200 μg/gPM in UA PM. The most prominent aldehydes were syringaldehyde and vanillin in WS PM and glyoxal in UA PM. The most abundant acids in both PM samples were short-chain dicarboxylic acids (≤C10). WS PM had a high abundance of hydroxyacids (vanillic and malic acids) as well as ketoacids (glutaric and oxalacetic) while UA PM also featured a high abundance of long-chain monocarboxylic acids (≥C16).
Prediction of Collision Cross Section and Retention Time for Broad Scope Screening in Gradient Reversed-Phase Liquid Chromatography-Ion Mobility-High Resolution Accurate Mass Spectrometry J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-15 Christian Brinch Mollerup, Marie Mardal, Petur Weihe Dalsgaard, Kristian Linnet, Leon Patrick Barron
Exact mass, retention time (RT), and collision cross section (CCS) are used as identification parameters in liquid chromatography coupled to ion mobility high resolution accurate mass spectrometry (LC-IM-HRMS). Targeted screening analyses are now more flexible and can be expanded for suspect and non-targeted screening. These allow for tentative identification of new compounds, and in-silico predicted reference values are used for improving confidence and filtering false-positive identifications. In this work, predictions of both RT and CCS values are performed with machine learning using artificial neural networks (ANNs). Prediction was based on molecular descriptors, 827 RTs, and 357 CCS values from pharmaceuticals, drugs of abuse, and their metabolites. ANN models for the prediction of RT or CCS separately were examined, and the potential to predict both from a single model was investigated for the first time. The optimized combined RT-CCS model was a four-layered multi-layer perceptron ANN, and the 95th prediction error percentiles were within 2 minutes RT error and 5% relative CCS error for the external validation set (n = 36) and the full RT-CCS dataset (n = 357). 88.6% (n = 733) of predicted RTs were within 2 minutes error for the full dataset. Overall, when using 2 minutes RT error and 5% relative CCS error, 91.9% (n = 328) of compounds were retained, while 99.4% (n = 355) were retained when using at least one of these thresholds. This combined prediction approach can therefore be useful for rapid suspect/non-targeted screening involving HRMS, and will support current workflows.
Advances in covalent organic frameworks in separation science J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-13 Hai-Long Qian, Cheng-Xiong Yang, Wen-Long Wang, Cheng Yang, Xiu-Ping Yan
A multilayer coil in type-I counter-current chromatography J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-13 Yi Yang, Jiao Yang, Chen Fang, Dongyu Gu, Ying Ma, Yoichiro Ito
In the present study, a novel model of type-I counter-current chromatography was developed to simplify the separation column manufacture and extend its application ranges. In this system, a multilayer coil was used as the separation column of type-I counter-current chromatography for the first time. The chromatographic performance of this apparatus was evaluated in terms of retention of the stationary phase (Sf), theoretical plate (N) and peak resolution (Rs) using dipeptides and DNP-amino acids as test samples with two classic solvent systems composed of 1-butanol-acetic acid-water (4:1:5, v/v) (BAW) and hexane-ethyl acetate-methanol-0.1 M HCl (1:1:1:1, v/v) (HEMW), respectively. The results indicated that the performance was optimal at the revolution speed of 200 rpm. The lower flow rate was more beneficial to retention of stationary phase and peak resolution. Over all results of our study revealed that the new type-I counter-current chromatography with a multilayer coil has a high application potential.
Bioanalysis of underivatized amino acids in noninvasive exhaled breath condensate samples using liquid chromatography coupled with tandem mass spectrometry ☆ J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-12 Lucyna Konieczna, Magdalena Pyszka, Magdalena Okońska, Maciej Niedźwiecki, Tomasz Bączek
Exhaled breath condensate (EBC) is receiving increased attention as a novel, entirely noninvasive technique for collecting biomarker samples. This increased attention is due to the fact that EBC is simple, effort independent, rapid, can be repeated frequently, and can be performed on young children and patients suffering from a variety of diseases. By having a subject breathe tidally through a cooling system for 15–20 minutes, a sufficient amount of condensate is collected for analysis of biomarkers in clinical studies. However, bioanalysis of EBC involves an unavoidable sample preparation step due to the low concentration of its components. Thus, there is a need for a new and more sensitive analytical method of assessing EBC samples. While researchers have considered analyses of single and small quantities of amino acids – for example, those connected with leukemia – no one has previously attempted to simultaneously analyze a panel of 23 amino acids. Moreover, the present study is well-justified, as prior studies focusing on single amino acids and leukemia at the moment of diagnosis and during chemotherapy (33 days of treatment) are inconsistent. In the present study, amino acids were separated using an XBridge Amide column (3 mm × 100 mm, 3.5 μm). The mobile phase consisted of 10 mM of ammonium buffer in water with a pH of 3 (Phase A) and 10 mM ammonium of buffer in acetonitrile (Phase B) under gradient program elution. The analytes were detected in electrospray positive ionization mode. Under optimal conditions, the proposed method exhibited limits of quantification (LOQ) in the range of 0.05–0.5 ng/mL, and good linearity, with determination coefficient (R2) falling between 0.9904 and 0.9998. The accuracy in human exhaled breath condensate samples ranged between 93.3–113.3% for the 23 studied amino acids, with intra- and inter-day coefficient of variation (CVs) of 0.13–9.92% and 0.17–10.53%, respectively. To demonstrate the liquid chromatography with hydrophilic interaction with electrospray source coupled to tandem mass spectrometry (LC-HILIC-ESI-MS/MS) method’s applicability for biomedical investigations, it was verified and applied to determine amino acids in pediatric patients with leukemia. These tests confirmed that glutamine, arginine, homoarginine, asparagine, histidine, methionone, proline, hydroxyproline, threonine, tyrosine, and valine were present in significantly higher levels in pediatric leukemia patients than in the healthy control group. The developed assay is an attractive alternative to standard analytical methods, because it allows for the non-invasive, fast, sensitive, and reliable analysis of amino acids without derivatization in EBC.
Modeling and simulation of protein elution in linear pH and salt gradients on weak, strong and mixed cation exchange resins applying an extended Donnan ion exchange model J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-12 Felix Wittkopp, Lars Peeck, Mathias Hafner, Christian Frech
Process development and characterization based on mathematic modeling provides several advantages and has been applied more frequently over the last few years. In this work, a Donnan equilibrium ion exchange (DIX) model is applied for modelling and simulation of ion exchange chromatography of a monoclonal antibody in linear chromatography. Four different cation exchange resin prototypes consisting of weak, strong and mixed ligands are characterized using pH and salt gradient elution experiments applying the extended DIX model. The modelling results are compared with the results using a classic stoichiometric displacement model. The Donnan equilibrium model is able to describe all four prototype resins while the stoichiometric displacement model fails for the weak and mixed weak/strong ligands. Finally, in silico chromatogram simulations of pH and pH/salt dual gradients are performed to verify the results and to show the consistency of the developed model.
Parallel loading and complete automation of a 3-step mAb purification process for multiple samples using a customized preparative chromatography instrument with networked pumps J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-12 Darren E. Ferguson, Evan R. Mahan, Weijun Ma, Gabrielle Bitzas, Xiaotian Zhong, Richard Zollner, Aaron M. D’Antona
Advancement in high-throughput screening methods of novel therapeutic proteins for early stage research and development, specifically mAbs, have given mid-scale (milligram to gram scale) purification groups access to more of these molecules. The available purification technologies built to support mid-scale production was not efficient or versatile enough to keep up with this surge. To remedy this problem, we have designed and built a custom instrument using an ÄKTA Pure. This system enables parallel processing up to 5 samples and has the versatility to perform 1- to 3-step purification processes in a single queue. Furthermore, a unique purification scheme can be selected for each of the five samples in the queue. Overall processing time has reduced by 83% compared to manual, non-parallel load methods Here, we describe our novel approach and demonstrate the flexibility, speed and efficiency of the instrument.
Study on the polymorphism of G-quadruplexes by reversed-phase HPLC and LC-MS J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-12 Jun-qin Qiao, Zhao-ming Cao, Chao Liang, Hong-juan Chen, Wei-juan Zheng, Hong-zhen Lian
Polymorphism is inherent for G-quadruplexes (G4s), and the different structural forms are important for the participation in different biological functions of telomeres. A lot of progress has been made in the exploration of G4 polymorphism. However, quick separation and reliable assessment methods for different conformations of G4 are still very few. In this work, the polymorphism of three sequences d[(G3T)3G3], d[(G3C)3G3] and d[(G3T)4] annealed in six different solutions were investigated by means of reversed-phase high performance liquid chromatography (RP-HPLC), liquid chromatography–mass spectrometry (LC-MS), fluorescence spectroscopy, circular dichroism spectroscopy, together with native-polyacrylamide gel electrophoresis. Different G4 conformations of these three sequences can be separated clearly by RP-HPLC, and further characterized by on-line LC-MS analysis. It is revealed that high-order structures other than intramolecular quadruplexes were favored for d[(G3T)3G3] and d[(G3C)3G3] under the annealing conditions. However, flanking loop impeded d[(G3T)4] to form higher-order structures than dimer. In addition, the nature and concentration of cation, as well as the annealing solution component, all have decent influence on the stability and relative ratios of various G4 building blocks. Based on the above findings, RP-HPLC and LC-MS combined with spectroscopic techniques can be used as a facile and powerful tool for quick separation and identification of G4s in solutions, and for effective assessment of DNA sequences and annealing environments on G4 polymorphism. The established protocol provides a novel strategy for evaluating G4 polymorphism, which will facilitate studies on quadruplex structures and their biophysical properties.
Automatic untargeted metabolic profiling analysis coupled with Chemometrics for improving metabolite identification quality to enhance geographical origin discrimination capability J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-10 Lu Han, Yue-Ming Zhang, Jing-Jing Song, Mei-Juan Fan, Yong-Jie Yu, Ping-Ping Liu, Qing-Xia Zheng, Qian-Si Chen, Chang-Cai Bai, Tao Sun, Yuan-Bin She
Untargeted metabolic profiling analysis is employed to screen metabolites for specific purposes, such as geographical origin discrimination. However, the data analysis remains a challenging task. In this work, a new automatic untargeted metabolic profiling analysis coupled with a chemometric strategy was developed to improve the metabolite identification results and to enhance the geographical origin discrimination capability. Automatic untargeted metabolic profiling analysis with chemometrics (AuMPAC) was used to screen the total ion chromatographic (TIC) peaks that showed significant differences among the various geographical regions. Then, a chemometric peak resolution strategy is employed for the screened TIC peaks. The retrieved components were further analyzed using ANOVA, and those that showed significant differences were used to build a geographical origin discrimination model by using two-way encoding partial least squares. To demonstrate its performance, a geographical origin discrimination of flaxseed samples from six geographical regions in China was conducted, and 18 TIC peaks were screened. A total of 19 significant different metabolites were obtained after the peak resolution. The accuracy of the geographical origin discrimination was up to 98%. A comparison of the AuMPAC, AMDIS, and XCMS indicated that AuMPACobtained the best geographical origin discrimination results. In conclusion, AuMPAC provided another method for data analysis.
A stochastic view on column efficiency J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-09 Fabrice Gritti
A stochastic model of transcolumn eddy dispersion along packed beds was derived. It was based on the calculation of the mean travel time of a single analyte molecule from one radial position to another. The exchange mechanism between two radial positions was governed by the transverse dispersion of the analyte across the column. The radial velocity distribution was obtained by flow simulations in a focused-ion-beam scanning electron microscopy (FIB-SEM) based 3D reconstruction from a 2.1 mm × 50 mm column packed with 2 μm BEH-C18 particles. Accordingly, the packed bed was divided into three coaxial and uniform zones: 1) a 1.4 particle diameter wide, ordered, and loose packing at the column wall (velocity uw u w ), 2) an intermediate 130 μm wide, random, and dense packing (velocity ui), and 3) the bulk packing in the center of the column (velocity uc). First, the validity of this proposed stochastic model was tested by adjusting the predicted to the observed reduced van Deemter plots of a 2.1 mm × 50 mm column packed with 2 μm BEH-C18 fully porous particles (FPPs). An excellent agreement was found for ui=0.93uc, a result fully consistent with the FIB-SEM observation (ui=0.95uc). Next, the model was used to measure ui=0.94uc for 2.1 mm × 100 mm column packed with 1.6 μm Cortecs-C18 superficially porous particles (SPPs). The relative velocity bias across columns packed with SPPs is then barely smaller than that observed in columns packed with FPPs (+6% versus + 7%). uw u w =1.8ui is measured for a 75 μm × 1 m capillary column packed with 2 μm BEH-C18 particles. Despite this large wall-to-center velocity bias (+80%), the presence of the thin and ordered wall packing layer has no negative impact on the kinetic performance of capillary columns. Finally, the stochastic model of long-range eddy dispersion explains why analytical (2.1 to 4.6 mm i.d.) and capillary (< 400 μm i.d.) columns can all be packed efficiently (1
3) with sub-2 μm particles and with 1 μm particles, respectively.
Retention prediction in reversed phase high performance liquid chromatography using quantitative structure-retention relationships applied to the Hydrophobic Subtraction Model J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-08 Yabin Wen, Mohammad Talebi, Ruth I.J. Amos, Roman Szucs, John W. Dolan, Christopher A. Pohl, Paul R. Haddad
Quantitative Structure-Retention Relationships (QSRR) methodology combined with the Hydrophobic Subtraction Model (HSM) have been utilized to accurately predict retention times for a selection of analytes on several different reversed phase liquid chromatography (RPLC) columns. This approach is designed to facilitate early prediction of co-elution of analytes, for example in pharmaceutical drug discovery applications where it is advantageous to predict whether impurities might be co-eluted with the active drug component. The QSRR model utilized VolSurf+ descriptors and a Partial Least Squares regression combined with a Genetic Algorithm (GA-PLS) to predict the solute coefficients in the HSM. It was found that only the hydrophobicity (η'H) term in the HSM was required to give the accuracy necessary to predict potential co-elution of analytes. Global QSRR models derived from all 148 compounds in the dataset were compared to QSRR models derived using a range of local modelling techniques based on clustering of compounds in the dataset by the structural similarity of compounds (as represented by the Tanimoto similarity index), physico-chemical similarity of compounds (represented by log D), the neutral, acidic, or basic nature of the compound, and the second dominant interaction between analyte and stationary phase after hydrophobicity. The global model showed reasonable prediction accuracy for retention time with errors of 30 s and less for up to 50% of modeled compounds. The local models for Tanimoto, nature of the compound and second dominant interaction approaches all exhibited prediction errors less than 30 s in retention time for nearly 70% of compounds for which models could be derived. Predicted retention times of five representative compounds on nine reversed-phase columns were compared with known experimental retention data for these columns and this comparison showed that the accuracy of the proposed modelling approach is sufficient to reliably predict the retention times of analytes based only on their chemical structures.
Automating Data Analysis for Two-Dimensional Gas Chromatography/Time-of-Flight Mass Spectrometry Non‐Targeted Analysis of Comparative Samples J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-07 Ivan A. Titaley, O. Maduka Ogba, Leah Chibwe, Eunha Hoh, Paul Cheong, Staci L. Massey Simonich
Non-targeted analysis of environmental samples, using comprehensive two‐dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC/ToF-MS), poses significant data analysis challenges due to the large number of possible analytes. Non-targeted data analysis of complex mixtures is prone to human bias and is laborious, particularly for comparative environmental samples such as contaminated soil pre- and post-bioremediation. To address this research bottleneck, we developed OCTpy, a Python™ script that acts as a data reduction filter to automate GC × GC/ToF-MS data analysis from LECO® ChromaTOF® software and facilitates selection of analytes of interest based on peak area comparison between comparative samples. We used data from polycyclic aromatic hydrocarbon (PAH) contaminated soil, pre- and post‐bioremediation, to assess the effectiveness of OCTpy in facilitating the selection of analytes that have formed or degraded following treatment. Using datasets from the soil extracts pre- and post‐bioremediation, OCTpy selected, on average, 18% of the initial suggested analytes generated by the LECO® ChromaTOF® software Statistical Compare feature. Based on this list, 63–100% of the candidate analytes identified by a highly trained individual were also selected by OCTpy. This process was accomplished in several minutes per sample, whereas manual data analysis took several hours per sample. OCTpy automates the analysis of complex mixtures of comparative samples, reduces the potential for human error during heavy data handling and decreases data analysis time by at least tenfold.
Porphyrin-based magnetic nanocomposites for efficient extraction of polycyclic aromatic hydrocarbons from water samples J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-07 Jing Yu, Shukui Zhu, Liling Pang, Pin Chen, Gang-Tian Zhu
Stable and reusable porphyrin-based magnetic nanocomposites were successfully synthesized for efficient extraction of polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. Meso-Tetra (4-carboxyphenyl) porphyrin (TCPP), a kind of porphyrin, can connect the copolymer after amidation and was linked to Fe3O4@SiO2 magnetic nanospheres via cross-coupling. Several characteristic techniques such as field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry, vibrating sample magnetometry and a tensiometer were used to characterize the as-synthesized materials. The structure of the copolymer was similar to that of graphene, possessing sp2-conjugated carbon rings, but with an appropriate amount of delocalized π-electrons giving rise to the higher extraction efficiency for heavy PAHs without sacrificing the performance in the extraction of light PAHs. Six extraction parameters, including the TCPP:Fe3O4@SiO2 (m:m) ratio, the amount of adsorbents, the type of desorption solvent, the desorption solvent volume, the adsorption time and the desorption time, were investigated. After the optimization of extraction conditions, a comparison of the extraction efficiency of Fe3O4@SiO2-TCPP and Fe3O4@SiO2@GO was carried out. The adsorption mechanism of TCPP to PAHs was studied by first-principles density functional theory (DFT) calculations. Combining experimental and calculated results, it was shown that the π-π stacking interaction was the main adsorption mechanism of TCPP for PAHs and that the amount of delocalized π-electrons plays an important role in the elution process. Under the optimal conditions, Fe3O4@SiO2-porphyrin showed good precision in intra-day (<8.9%) and inter-day (<13.0%) detection, low method detection limits (2–10 ng L−1), and wide linearity (10–10000 ng L−1). The method was applied to simultaneous analysis of 15 PAHs with acceptable recoveries, which were 71.1%-106.0% for ground water samples and 73.7%–107.1% for Yangtze River water samples, respectively.
A method for screening active components from Chinese herbs by cell membrane chromatography-offline-high performance liquid chromatography/mass spectrometry and an online statistical tool for data processing J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-06 Yan Cao, Shaozhan Wang, Yinghua Li, Xiaofei Chen, Langdong Chen, Dongyao Wang, Zhenyu Zhu, Yongfang Yuan, Diya Lv
Cell membrane chromatography (CMC) has been successfully applied to screen bioactive compounds from Chinese herbs for many years, and some offline and online two-dimensional (2D) CMC-high performance liquid chromatography (HPLC) hyphenated systems have been established to perform screening assays. However, the requirement of sample preparation steps for the second-dimensional analysis in offline systems and the need for an interface device and technical expertise in the online system limit their extensive use. In the present study, an offline 2D CMC-HPLC analysis combined with the XCMS (various forms of chromatography coupled to mass spectrometry) Online statistical tool for data processing was established. First, our previously reported online 2D screening system was used to analyze three Chinese herbs that were reported to have potential anti-inflammatory effects, and two binding components were identified. By contrast, the proposed offline 2D screening method with XCMS Online analysis was applied, and three more ingredients were discovered in addition to the two compounds revealed by the online system. Then, cross-validation of the three compounds was performed, and they were confirmed to be included in the online data as well, but were not identified there because of their low concentrations and lack of credible statistical approaches. Last, pharmacological experiments showed that these five ingredients could inhibit IL-6 release and IL-6 gene expression on LPS-induced RAW cells in a dose-dependent manner. Compared with previous 2D CMC screening systems, this newly developed offline 2D method needs no sample preparation steps for the second-dimensional analysis, and it is sensitive, efficient, and convenient. It will be applicable in identifying active components from Chinese herbs and practical in discovery of lead compounds derived from herbs.
Investigating the causes of low detectability of pesticides in fruits and vegetables analysed by high-performance liquid chromatography – Time-of-flight J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-06 S. Muehlwald, N. Buchner, L.W. Kroh
Because of the high number of possible pesticide residues and their chemical complexity, it is necessary to develop methods which cover a broad range of pesticides. In this work, a qualitative multi-screening method for pesticides was developed by use of HPLC-ESI-Q-TOF. 110 pesticides were chosen for the creation of a personal compound database and library (PCDL). The MassHunter Qualitative Analysis software from Agilent Technologies was used to identify the analytes. The software parameter settings were optimised to produce a low number of false positive as well as false negative results. The method was validated for 78 selected pesticides. However, the validation criteria were not fulfilled for 45 analytes. Due to this result, investigations were started to elucidate reasons for the low detectability. It could be demonstrated that the three main causes of the signal suppression were the co-eluting matrix (matrix effect), the low sensitivity of the analyte in standard solution and the fragmentation of the analyte in the ion source (in-source collision-induced dissociation). In this paper different examples are discussed showing that the impact of these three causes is different for each analyte. For example, it is possible that an analyte with low signal intensity and an intense fragmentation in the ion source is detectable in a difficult matrix, whereas an analyte with a high sensitivity and a low fragmentation is not detectable in a simple matrix. Additionally, it could be shown that in-source fragments are a helpful tool for an unambiguous identification.
Surface Enhanced Raman Spectroscopy in Microchip Electrophoresis ☆ J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-06 Anna Tycova, Renata F. Gerhardt, Detlev Belder
Coupling microchip capillary electrophoresis to surface enhanced Raman spectroscopy (MCE-SERS) combines the high separation power of capillary electrophoresis with the capability to obtain vibrational fingerprint spectra for compound identification. Raman spectroscopy is a structurally descriptive and label-free detection method which is particularly suited for chemical analysis because it is non-destructive and allows the identification of analytes. However, it suffers from poor sensitivity and sometimes even requires acquisition times far longer than the typical peak width of electrophoretic separations. The Raman intensity can be drastically improved if the analyte is brought into close proximity to nanostructured metal surfaces or colloids due to the surface enhancement effect. This paper presents a novel approach in the field of MCE-SERS on-line coupling. The key element of the developed glass microfluidic device is a dosing structure which consists of two side channels joining the MCE channel symmetrically after the electrophoretic separation of the analytes. The dosing channel supplies silver nanoparticles (Ag-NPs), to the separated electrophoretic zones which facilitates an on-the-fly recording of SERS-spectra of the separated compounds. The functionality of the MCE-SERS chip was evaluated by the analysis of a rhodamine model mixture within 90 seconds achieving RSD of migration times below 1.5%. The approach was successfully applied for the analysis of the food additive riboflavin in a barbecue sauce.
Critical evaluation of several techniques for the analysis of phthalates and terephthalates; application to liquids used in electronic cigarettes J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-06 Serban C. Moldoveanu, Ravikiran Yerabolu
This study describes several original methods that were developed with the goal of measuring phthalates and terephthalates. These methods include gas chromatography/mass spectrometry (GC/MS), GC/MS/MS, liquid chromatography with UV detection (LC/UV), LC/MS, and LC/MS/MS. The study compares the advantages and disadvantages of these methods and their applicability to measuring phthalates and terephthalates in the liquids used in electronic cigarettes (e-liquids). The analytes evaluated include eight phthalates and two terephthalates. The phthalates were diethyl, dibutyl, benzyl butyl, diphenyl, bis(2-ethylhexyl), di-n-octyl, diisononyl and diisodecyl. The terephthalates were dimethyl and bis(2-ethylhexyl). The methods used two chromatographic standards, dimethyl phthalate-3,4,5,6-d4, and di-(2-ethylhexyl) phthalate-3,4,5,6-d4. All techniques were validated for selectivity/specificity, precision, sensitivity (evaluation of LOD and LOQ), as well as for repeatability and matrix interference. The GC methods were not adequate for the analysis of diphenyl, diisononyl, and diisodecyl phthalates which were not volatile enough to be seen in the conditions used for the GC separation. Also, alcohols should not be used as solvents for the injection of the sample in the GC system to avoid transesterification in the hot injection port. The single quadrupole MS detection in GC offers sensitivities around 1 μg/mL in the e-liquid and was not sensitive enough for the analysis of trace phthalates and terephthalates. Compared to all evaluated methods, the MS/MS detection in GC offered the best sensitivity (below 10 ng/mL in the e-liquid). The LC is adequate for the separation of all the evaluated analytes. However, the UV detection in LC does not offer good sensitivity compared to all the other techniques. The MS detection in LC provides poor sensitivity for terephthalates, but better than the UV for the rest of the analytes. The MS/MS detection for LC offers slightly better sensitivity than the MS detection, but both LC/MS and LC/MS/MS were only able to measure levels above about 100 ng/mL of analytes in the e-liquid. A group of 39 e-liquids were analyzed by three of the evaluated procedures. Benzyl butyl phthalate, bis(2-ethylhexyl) terephthalate, and di-n-octyl phthalate were not detected in the e-liquids. Some of the other evaluated phthalates were present at trace levels in certain e-liquids while most e-liquids did not contain phthalates at detectable levels.
Comprehensive on-line two-dimensional liquid chromatography × supercritical fluid chromatography with trapping column-assisted modulation for depolymerised lignin analysis J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-06 Mingzhe Sun, Margareta Sandahl, Charlotta Turner
Lignin depolymerisation produces a large variety of low molecular weight phenolic compounds that can be upgraded to value-added chemicals. Detailed analysis of these complex depolymerisation mixtures are, however, hampered by the lack of resolving power of traditional analysis techniques. In this study, a novel online comprehensive two-dimensional reversed-phase liquid chromatography (RPLC) × supercritical fluid chromatography (SFC) method with trapping column interface was developed for the separation of phenolic compounds in depolymerised lignin samples. The trapping capacities of different trapping columns were evaluated. The influence of large volume water-containing injection on SFC performance was studied. The relation between peak capacity and first dimension flow rate and gradient was investigated. The optimized method was applied for the analysis of a depolymerised lignin sample. The RPLC × SFC system exhibited high degree of orthogonality. Compared with traditional loop based interface, trapping column interface can significantly shorten the analysis time and offer higher detectability, with the disadvantage of more severe undersampling in the first dimension.
Homochiral zeolite-like metal-organic framework with DNA like double-helicity structure as stationary phase for capillary electrochromatography enantioseparation J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-06 Congjie Pan, Wenjuan Lv, Xiaoying Niu, Guoxiu Wang, Hongli Chen, Xingguo Chen
In recent years, artificial materials with double helix structure have attracted widespread attention due to their unique properties such as the DNA like double-helicity, intrinsic chirality and diverse functional groups. Developing novel chiral stationary phases (CSPs) for capillary electrochromatography enantioseparation is of intriguing interest. Herein, a novel homochiral zeolite-like metal-organic framework (ZMOF) JLU-Liu23 with unique DNA like double-helicity structure was firstly utilized as the CSP in open tubular capillary electrochromatography (OT-CEC) for enantioseparation of chiral monoamine neurotransmitters and analogues. Owing to the unique DNA like double-helicity structure of the homochiral ZMOF JLU-Liu23, the good enantioseparation of four monoamine neurotransmitters and analogues was achieved on the prepared homochiral ZMOF JLU-Liu23 coated capillary column. The relative standard deviations (RSDs) of the analytes migration time for intra-day, inter-day and column-to-column were in the range of 0.3–0.6%, 0.8–2.2% and 3.5–6.5%, respectively.
Core-shell structured magnetic metal-organic framework composites for highly selective detection of N-glycopeptides based on boronic acid affinity chromatography J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-06 Yiqin Xie, Qianjing Liu, Yan Li, Chunhui Deng
Boronic acid affinity chromatography (BAAC) is one of the most significant methods in glycoproteomics research due to its low bias towards glycopeptides and easy enrichment process. In this work, core-shell structured magnetic metal-organic framework (MOF) composites with abundant boronic acid groups were designed and synthesized for selective glycopeptide enrichment based on BAAC. The as-prepared core-shell structured magnetic MOF composites (denoted as Fe3O4@PVP/PEI@MOF (B)) inherited strong magnetic responsiveness from the Fe3O4 core as well as ultrahigh surface area and abundant boronic acid sites from the MOF shell. The affinity between boronic acid and cis-diols groups endowed the composites with improved sensitivity (0.5 fmol/μL) and selectivity (1:100) towards glycopeptides, achieving remarkable results in glycopeptides detection from standard glycoprotein digests as well as complex bio-samples. As a result, a total of 209 N-glycosylation peptides from 89 different glycoproteins were identified from human serum digests, indicating its broad prospect in glycoproteome study.
Tetrafluoroterephthalonitrile-crosslinked β-cyclodextrin polymers for efficient extraction and recovery of organic micropollutants from water J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-06 Chenjun Li, Max J. Klemes, William R. Dichtel, Damian E. Helbling
In this study, we evaluated the performance of a novel tetrafluoroterephthalonitrile-crosslinked β-cyclodextrin polymer (TFN-CDP) as a solid-phase extraction (SPE) material for the recovery of up to 189 diverse organic micropollutants (MPs) from water. The optimized extraction procedure requires loading of water samples adjusted to a pH of 3 onto 500 mg of TFN-CDP packed into an SPE cartridge. Under these conditions, 88.7% of the MPs have average extraction efficiencies greater than 80%. The optimized recovery procedure requires elution with 15 mL of methanol amended with 15 mg of calcium chloride. Under these conditions, 58.4% of the MPs have average absolute recoveries between 80% and 120%. We compared the performance of the optimized SPE method for TFN-CDP with a previously optimized SPE method employing hydrophilic-lipophilic balance (HLB) adsorbents in nanopure water and in wastewater-impacted surface water. The data indicate that the optimized TFN-CDP method performs as well as or better than the optimized HLB-based SPE method. These findings represent an important step forward in the development of sustainable and inexpensive materials for the extraction and recovery of organic MPs from water.
Thermally condensed humic acids onto silica as SPE for effective enrichment of glucocorticoids from environmental waters followed by HPLC-HESI-MS/MS J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-05 Andrea Speltini, Francesca Merlo, Federica Maraschi, Michela Sturini, Matteo Contini, Nicola Calisi, Antonella Profumo
Pristine humic acids (HAs) were thermally condensed onto silica microparticles by a one-pot, inexpensive and green preparation route obtaining a mixed-mode sorbent (HA-C@silica) with good sorption affinity for glucocorticoids (GCs). The carbon-based material, characterized by various techniques, was indeed applied as the sorbent for fixed-bed solid-phase extraction of eight GCs from river water and wastewater treatment plant effluent, spiked at different concentration levels in the range 1–400 ng L−1. After sample extraction, the target analytes were simultaneously and quantitatively eluted in a single fraction of methanol, achieving enrichment factor 4000and 1000 in river water and wastewater effluent, respectively. Full recovery for all compounds, was gained in the real matrices studied (80–125% in river water, 79–126% in wastewater effluent), with inter-day precision showing relative standard deviations (RSD) below 15% and 18% (n = 3), for river and wastewater effluent, correspondingly. The high enrichment factors coupled with high-performance liquid chromatography tandem mass spectrometry quantification (MRM mode) provided method quantification limits of 0.009–0.48 ng L−1 in river water and 0.06–3 ng L−1 in wastewater effluent and, at the same time, secure identification of the selected drugs. As also evidenced by comparison with literature, HA-C@silica proved to be a valid alternative to the current commercial sorbents, in terms of extraction capability, enrichment factor, ease of preparation and cost. The batch-to-batch reproducibility was assessed by recovery tests on three independently prepared HA-C@silica powders (RSD lower than 7%).
CAPILLARY LIQUID CHROMATOGRAPHY-ION TRAP-MASS SPECTROMETRY METHODOLOGY FOR THE SIMULTANEOUS QUANTIFICATION OF FOUR ANGIOTENSIN-CONVERTING ENZYME-INHIBITORY PEPTIDES IN PRUNUS SEED HYDROLYSATES J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-05 Estefanía González-García, María Concepción García, María Luisa Marina
Prunus genus fruit seeds are sources of highly angiotensin-I-converting enzyme (ACE)‐inhibitory peptides. The presence of peptides IYSPH, IYTPH, IFSPR, and VAIP seems to be related to this activity but no previous work has demonstrated the direct relationship between the concentration of these peptides and the antihypertensive activity of hydrolysates. This work describes the development of a method for the quantification of these peptides in Prunus seeds hydrolysates based on capillary liquid chromatography‐IT-MS/MS. The analytical characteristics of the method were evaluated through the study of the linearity, LOD, LOQ, presence of matrix interferences, precision, and recovery. The developed methodology was applied to the determination of the four peptides in seed hydrolysates from different Prunus genus fruits: peaches (7 varieties), plums (2 varieties), nectarines (3 varieties), apricots (2 varieties), cherry, and paraguayo. Peaches and plums seed hydrolysates yielded the highest concentrations of these peptides while paraguayo one showed the lowest concentrations. A high correlation between peptides concentrations was demonstrated suggesting that the four peptides could be released from the same seed proteins.
Dendritic core-shell silica spheres with large pore size for separation of biomolecules J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-04 Qishu Qu, Yang Si, Han Xuan, Kehua Zhang, Xiaoming Chen, Yi Ding, Shaojie Feng, Han-Qing Yu, M. Asiri Abdullah, Khalid A. Alamry
Monodispersed core-shell silica spheres with fibrous shell structure and tunable pore size were prepared by using a one-pot oil-water biphase method. The pore size could be tuned from 7 nm to 37 nm by using organic solvents with different polarities as oil phase. The spheres synthesized by using benzene as organic solvent had the maximum pore size of 37 nm and possessed a surface area of 61 m2 g−1. The obtained wide pore core-shell silica spheres were applied for rapidly separating small molecules, peptides, small proteins, and large proteins with molecular weight up to 200 kDa. Since the pore size of the core-shell silica spheres was sufficiently large for the free access of all the solutes, sharp and symmetric peaks were obtained. The separation performance was as high as 264531 plates m−1 for fluorene. The great efficient separation demonstrates that the wide pore core-shell silica spheres have a great potential for rapid analysis of both small and large solutes with high performance liquid chromatography.
Thermodynamics of acid-base dissociation of several cathinones and 1‐phenylethylamine, studied by an accurate capillary electrophoresis method free from the Joule heating impact J. Chromatogr. A (IF 3.981) Pub Date : 2018-02-03 Paweł Mateusz Nowak, Michał Woźniakiewicz, Mariusz Mitoraj, Filip Sagan, Paweł Kościelniak
Capillary electrophoresis is often used to the determination of the acid-base dissociation/deprotonation constant (pKa), and the more advanced thermodynamic quantities describing this process (ΔH°, -TΔS°). Remarkably, it is commonly overlooked that due to insufficient dissipation of Joule heating the accuracy of parameters determined using a standard approach may be questionable. In this work we show an effective method allowing to enhance reliability of these parameters, and to estimate the magnitude of errors. It relies on finding a relationship between electrophoretic mobility and actual temperature, and performing pKa determination with the corrected mobility values. It has been employed to accurately examine the thermodynamics of acid-base dissociation of several amine compounds − known for their strong dependency of pKa on temperature: six cathinones (2-methylmethcathinone, 3‐methylmethcathinone, 4-methylmethcathinone, α‐pyrrolidinovalerophenone, methylenedioxypyrovalerone, and ephedrone); and structurally similar 1‐phenylethylamine. The average pKa error caused by Joule heating noted at 25 °C was relatively small − 0.04-0.05 pH unit, however, a more significant inaccuracy was observed in the enthalpic and, in particular, entropic terms. An alternative correction method has also been proposed, simpler and faster, but not such effective in correcting ΔH°/-TΔS° terms. The corrected thermodynamic data have been interpreted with the aid of theoretical calculations, on a ground of the enthalpy-entropy relationships and the most probable structural effects accounting for them. Finally, we have demonstrated that the thermal dependencies of electrophoretic mobility, modelled during the correction procedure, may be directly used to find optimal temperature providing a maximal separation efficiency.
Guanidinium ionic liquid-based surfactants as low cytotoxic extractants: Analytical performance in an in-situ dispersive liquid–liquid microextraction method for determining personal care products J. Chromatogr. A (IF 3.981) Pub Date : 2017-05-01 Idaira Pacheco-Fernández, Verónica Pino, Juan H. Ayala, Ana M. Afonso
The IL-based surfactant octylguanidinium chloride (C8Gu-Cl) was designed and synthetized with the purpose of obtaining a less harmful surfactant: containing guanidinium as core cation and a relatively short alkyl chain. Its interfacial and aggregation behavior was evaluated through conductivity and fluorescence measurements, presenting a critical micelle concentration value of 42.5 and 44.6 mmol L−1, respectively. Cytotoxicity studies were carried out with C8Gu-Cl and other IL-based and conventional surfactants, specifically the analogue 1-octyl-3-methylimidazolium chloride (C8MIm-Cl), and other imidazolium- (C16MIm-Br) and pyridinium- (C16Py-Cl) based surfactants, together with the conventional cationic CTAB and the conventional anionic SDS. From these studies, C8Gu-Cl was the only one to achieve the classification of low cytotoxicity. An in situ dispersive liquid–liquid microextraction (DLLME) method based on transforming the water-soluble C8Gu-Cl IL-based surfactant into a water-insoluble IL microdroplet via a simple metathesis reaction was then selected as the extraction/preconcentration method for a group of 6 personal care products (PCPs) present in cosmetic samples. The method was carried out in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD). The method was properly optimized, requiring the use of only 30 μL of C8Gu-Cl for 10 mL of aqueous sample with a NaCl content of 8% (w/v) to adjust the ionic strength and pH value of 5. The metathesis reaction required the addition of the anion exchange reagent (bis[(trifluoromethyl)sulfonyl]imide − 1:1 molar ratio), followed by vortex and centrifugation, and dilution of the final microdroplet up to 60 μL with acetonitrile before the injection in the HPLC-DAD system. The optimum in situ DLLME-HPLC-DAD method takes ∼10 min for the extraction step and ∼22 min for the chromatographic separation, with analytical features of low detection limits: down to 0.4 μg L−1; high reproducibility: with RSD values lower than 10% (intra-day) and 16% (inter-day) for a spiked level of 15 μg L−1; and an average enrichment factor of 89. The requirement of low volumes (30 μL) of a low cytotoxic IL-based surfactant allows the method to be considered less harmful than other common analytical microextraction approaches.
Determination of piperidinium ionic liquid cations in environmental water samples by solid phase extraction and hydrophilic interaction liquid chromatography J. Chromatogr. A (IF 3.981) Pub Date : 2017-05-08 Zi-qiang Fan, Hong Yu
This paper presents a novel analytical method for the determination of piperidinium ionic liquid cations in environmental water by hydrophilic interaction liquid chromatography and solid-phase extraction technology. The left standing, centrifuged and filtered river water samples were first purified and concentrated through the C18 solid phase extraction column, and eluted with 0.02 mol/L hydrochloric acid prepared in methanol and deionized water (80/20, v/v). Then the eluents were analyzed by a hydrophilic column combined with 0.8 mmol/L 1-propyl-3-methyl imidazolium tetrafluoroborate aqueous solution/acetonitrile (40/60, v/v) as the mobile phase and indirect ultraviolet detection. The detection limits of piperidinium cations were less than 0.4 mg/L. The relative standard deviations were less than 0.6%. The method has been successfully applied to the determination of piperidinium cations in Songhua River water samples. Recoveries were 80.0%–98.3%. This research may provide a reference for studying the environmental effect of ionic liquids.
Extent of the influence of phosphate buffer and ionic liquids on the reduction of the silanol effect in a C18 stationary phase J. Chromatogr. A (IF 3.981) Pub Date : 2017-06-01 S. Carda-Broch, M.C. García-Alvarez-Coque, M.J. Ruiz-Angel
The presence of anionic free silanols in the silica-based stationary phases gives rise to broad and asymmetrical peaks when cationic basic compounds are chromatographed using hydro-organic mobile phases. The addition to the mobile phase of a reagent with ionic character prevents the access of analytes to the free silanols, improving the peak shape. The silanol activity can be affected by the buffer concentration and mobile phase pH, factors that are not always considered sufficiently in the literature. In this work, the chromatographic behaviour of three basic β‐adrenoceptor antagonists (acebutolol, nadolol and timolol), using mobile phases containing acetonitrile, was examined at different phosphate buffer concentrations (5–50 mM) and mobile phase pH (2–8), in the absence and presence of three imidazolium-based ionic liquids (1‐ethyl-, 1‐butyl- and 1-hexyl-3-methylimidazolium chloride). All factors were evaluated through both the retention and peak shape. The imidazolium cations can block the access of cationic analytes through electrostatic interaction with the anionic silanols, or association with the alkyl chains bound to the stationary phase. In previous reports, the protection mechanism was demonstrated to be directly related to the cation size. The studies in this work reveal that the effectiveness of the mobile phase additive as silanol blocker also depends on the concentration of the buffer anion and the protonation degree of the silanols on the stationary phase. Increasing amounts of phosphate at low pH give rise to increasing retention times. Also, the peak shape is improved, which indicates the influence of phosphate on blocking the activity of free silanols. However, the benefits obtained by the combined effect of buffering the mobile phase at low pH and the use of a bulky additive are lost at pH > 6.
Establishment and molecular modeling study of maltodextrin-based synergistic enantioseparation systems with two new hydroxy acid chiral ionic liquids as additives in capillary electrophoresis J. Chromatogr. A (IF 3.981) Pub Date : 2017-06-02 Xuan Yang, Yingxiang Du, Zijie Feng, Zongran Liu, Jingtang Li
Discovering more superior performance of ionic liquids for the separation science has triggered increasing interest. In this work, two new Hydroxy acid-based chiral ionic liquids (CILs) (tertramethylammonium-d-pantothenate (TMA-d-PAN), tertramethylammonium-d-quinate (TMA-d-QUI)) were designed and first used as additives to establish the maltodextrin-based synergistic systems for enantioseparation in capillary electrophoresis (CE). Compared to traditional single maltodextrin chiral separation system, significantly improved separations of all tested drugs in the CIL/Maltodextrin synergistic systems were obtained. Some parameters (CIL concentration, maltodextrin concentration, buffer pH, and applied voltage) in the TMA-d-PAN/Maltodextrin synergistic system have been examined and optimized for analytes. The molecular docking software AutoDock was applied to simulate the recognition process and surmise feasible resolution mechanism in the Maltodextrin/CILs synergistic systems, which has certain guiding value.
A system map for the ionic liquid stationary phase 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethylsulfonyl)imide trifluoromethanesulfonate for gas chromatography J. Chromatogr. A (IF 3.981) Pub Date : 2017-06-08 Nicole Lenca, Colin F. Poole
The solvation parameter model is used to prepare a system map for the retention of volatile organic compounds on the ionic liquid stationary phase 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethylsulfonyl)imide trifluoromethanesulfonate (SLB-IL61) over the temperature range 80–260 °C. Retention is governed by dispersion, dipole-type and hydrogen-bonding interactions each with its own temperature dependence. The exchange of a bis(trifluoromethylsulfonyl)imide anion in SLB-IL60 for a trifluromethanesulfonate anion (SLB-IL61) results in a change in selectivity indicated by an increase in the hydrogen-bond basicity and a decrease in hydrogen-bond acidity of the stationary phase without change in either the cohesion or dipolarity/polarizability of the stationary phases. At high temperatures there are small differences in electron lone pair interactions but these are relatively unimportant in terms of selectivity differences. Since the disclosed chemical structures for SLB-IL60 and SLB-IL61 does not contain obvious hydrogen-bond acid functional groups the modest hydrogen-bond acidity of these stationary phases was unexpected but does not appear to be obviously connected to adsorption sites at the column wall. The polarity number is shown to be a poor indicator of column retention properties for SLB-IL61. Principal component analysis with the system constants as variables indicates that the retention properties of SLB-IL61 are not duplicated by any of the common poly(siloxane) and poly(ethylene glycol) stationary phase chemistries in current use for column preparation. The SLB-IL61 column is closest in separation properties to poly(cyanopropylphenyldimethylsiloxane) and poly(cyanopropylmethyldimethysiloxane) stationary phases with a high percentage of cyanopropyl-containing monomer but the two stationary phase types are not selectivity equivalent.
Surface-bonded amide-functionalized imidazolium ionic liquid as stationary phase for hydrophilic interaction liquid chromatography J. Chromatogr. A (IF 3.981) Pub Date : 2017-07-12 Lizhen Qiao, Wangjie Lv, Mengmeng Chang, Xianzhe Shi, Guowang Xu
The amide group modified silica materials are popular stationary phases for hydrophilic interaction liquid chromatography (HILIC). Meanwhile, surface-confined imidazolium ionic liquids (ILs) have been proved to be useful HILIC stationary phases and possess many unique properties. In this study, the synthesis of an amide-functionalized imidazolium IL was conducted which was then bonded onto silica surface to obtain a novel imidazolium-embedded amide stationary phase for HILIC. The combination of the amide group and imidazolium IL moiety might bring some advantages in selectivity or retention and therefore extended its applications. After characterizing the prepared IL and the resulting modified silica materials, the chromatographic performance and separation selectivity of the packed column were evaluated and compared with a commercial amide column. Then, the retention behavior was investigated through observing the retention factors at different chromatographic conditions using a wide range of compounds. Exceptionally, the prepared amide IL column exhibited superior separation performance towards complex samples such as flavonoids mixture, soybean flavonoids and human urine. All the results indicated that the novel amide IL column possessed an anion-exchange/HILIC mixed-mode retention mechanism and could be useful in the sample analysis as a promising candidate for HILIC stationary phase.
Simultaneous extraction and concentration of water pollution tracers using ionic-liquid-based systems J. Chromatogr. A (IF 3.981) Pub Date : 2017-07-29 Teresa B.V. Dinis, Helena Passos, Diana L.D. Lima, Ana C.A. Sousa, João A.P. Coutinho, Valdemar I. Esteves, Mara G. Freire
Human activities are responsible for the release of innumerous substances into the aquatic environment. Some of these substances can be used as pollution tracers to identify contamination sources and to prioritize monitoring and remediation actions. Thus, their identification and quantification are of high priority. However, due to their presence in complex matrices and at significantly low concentrations, a pre-treatment/concentration step is always required. As an alternative to the currently used pre-treatment methods, mainly based on solid-phase extractions, aqueous biphasic systems (ABS) composed of ionic liquids (ILs) and K3C6H5O7 are here proposed for the simultaneous extraction and concentration of mixtures of two important pollution tracers, caffeine (CAF) and carbamazepine (CBZ). An initial screening of the IL chemical structure was carried out, with extraction efficiencies of both tracers to the IL-rich phase ranging between 95 and 100%, obtained in a single-step. These systems were then optimized in order to simultaneously concentrate CAF and CBZ from water samples followed by HPLC-UV analysis, for which no interferences of the ABS phase-forming components and other interferents present in a wastewater effluent sample have been found. Based on the saturation solubility data of both pollution tracers in the IL-rich phase, the maximum estimated concentration factors of CAF and CBZ are 28595- and 8259-fold. IL-based ABS can be thus envisioned as effective pre-treatment techniques of environmentally-related aqueous samples for a more accurate monitoring of mixtures of pollution tracers.
Recent advances on ionic liquid uses in separation techniques J. Chromatogr. A (IF 3.981) Pub Date : 2017-09-22 A. Berthod, M.J. Ruiz-Ángel, S. Carda-Broch
The molten organic salts with melting point below 100 °C, commonly called ionic liquids (ILs) have found numerous uses in separation sciences due to their exceptional properties as non molecular solvents, namely, a negligible vapor pressure, a high thermal stability, and unique solvating properties due to polarity and their ionic character of molten salts. Other properties, such as viscosity, boiling point, water solubility, and electrochemical window, are adjustable playing with which anion is associated with which cation. This review focuses on recent development of the uses of ILs in separation techniques actualizing our 2008 article (same authors, J. Chromatogr. A, 1184 (2008) 6–18) focusing on alkyl methylimidazolium salts. These developments include the use of ILs in nuclear waste reprocessing, highly thermally stable ILs that allowed for the introduction of polar gas chromatography capillary columns able to work at temperature never seen before (passing 300 °C), the use of ILs in liquid chromatography and capillary electrophoresis, and the introduction of tailor-made ILs for mass spectrometry detection of trace anions at the few femtogram level. The recently introduced deep eutectic solvents are not exactly ILs, they are related enough so that their properties and uses in countercurrent chromatography are presented.
Applications of ionic liquids in biphasic separation: Aqueous biphasic systems and liquid–liquid equilibria J. Chromatogr. A (IF 3.981) Pub Date : 2017-10-10 Shashi Kant Shukla, Shubha Pandey, Siddharth Pandey
Ionic liquids (ILs) have been receiving much attention in many fields of analytical chemistry because of their various interesting properties which distinguish them from volatile organic compounds. They offer both directional and non-directional forces towards a solute molecule and therefore act as excellent solvents for a wide range of polar and non-polar compounds. Because of the presence of various possible interactions, ILs easily undergo biphasic separation with water and other less polar/non-polar organic solvents. Their ability to create biphasic splitting makes them a promising candidate for liquid–liquid separation processes, such as aqueous biphasic systems and liquid–liquid equilibria. Various aspects of ILs in these separation methods are discussed in view of the origin of physical forces responsible for the biphasic interactions, the effect of structural components, temperature, pressure, pH and additives. The specific advantages of using ILs in aqueous biphasic systems and liquid–liquid equilibria in binary and ternary systems are discussed with a view to defining their future role in separation processes by giving major emphasis on developing non-toxic ILs with physical and solution properties tailored to the needs of specific sample preparation techniques.
Suitability of 1-hexyl-3-methylimidazolium ionic liquids for the analysis of pharmaceutical formulations containing tricyclic antidepressants J. Chromatogr. A (IF 3.981) Pub Date : 2017-11-27 S. Calabuig-Hernández, E. Peris-García, M.C. García-Alvarez-Coque, M.J. Ruiz-Angel
The reversed-phase chromatographic behaviour of six tricyclic antidepressants (amitryptiline, clomipramine, doxepin, imipramine, nortryptiline and maprotiline) was examined in this work with acetonitrile-water mobile phases, in the absence and presence of the ionic liquids 1-hexyl-3-methylimidazolium chloride and 1-hexyl-3-methylimidazolium tetrafluoroborate, which have interesting features for the separation of basic compounds, in terms of peak shape combined with reduced retention. Tricyclic antidepressants are low polarity drugs that strongly associate to the alkyl chains of conventional stationary phases. They are also positively charged in the usual working pH range (2–8) in reversed-phase liquid chromatography, due to their strong basic character. In consequence, they may interact with the residual ionised silanols present in conventional silica-based stationary phases, which is translated in stronger retention, and tailed and broad peaks. A simple chromatographic procedure for the control of tricyclic antidepressants in pharmaceutical formulations was developed using a C8 column and a mobile phase containing 30% acetonitrile/10 mM 1-hexyl-3-methylimidazolium chloride at pH 3, with UV detection. Intra- and inter-day precisions were usually below +1.0%, and intra- and inter-day bias (trueness) ranged between ‒2.1% and +2.4%, and between ‒3.0% and +2.3%, respectively. Sample preparation was simple and only required solubilisation and filtration previous to injection.
Synthesis and application of ionic liquid functionalized β-cyclodextrin, mono-6-deoxy-6-(4-amino-1,2,4-triazolium)-β-cyclodextrin chloride, as chiral selector in capillary electrophoresis J. Chromatogr. A (IF 3.981) Pub Date : 2017-11-29 Jingtang Li, Tao Yu, Guangfu Xu, Yingxiang Du, Zongran Liu, Zijie Feng, Xuan Yang, Ying Xi, Jie Liu
Recently,ionic liquids (ILs) functionalized cyclodextrins (CDs) have attracted more and more attention in the fields of enantioseparation. In this study, a novel IL amino triazolium functionalized β-CD derivative, mono-6-deoxy-6-(4-amino-1,2,4-triazolium)-β-cyclodextrin chloride (4-ATMCDCl), was synthesized for the first time and managed to separate dansyl amino acids and naproxen by capillary electrophoresis (CE). Compared with native β-CD, the new selector exhibited good water solubility and enhanced enantioselectivity. Several crucial parameters such as selector concentration, buffer pH, and applied voltage were systematically investigated. The molecular docking program Autodock was applied to further demonstrate the mechanism of chiral recognition and the enhanced enantioselectivity of 4-ATMCDCl, which showed good agreement with our experimental results.
Supercritical water-treated fused silica capillaries in analytical separations: Status review J. Chromatogr. A (IF 3.981) Pub Date : 2018-01-31 Pavel Karásek, Marie Horká, Karel Šlais, Josef Planeta, Michal Roth
Near- and supercritical water (SCW) has recently been shown to provide an unusual but effective tool to roughen the inner surface or manipulate the internal diameter of fused silica capillaries for analytical separation methods In this review, the to-date existing variants of instrumental arrangement for etching the fused silica capillaries with SCW are described, the currently accessible morphologies of SCW-etched capillaries are outlined, and both existing and prospective applications of the SCW-etched capillaries in analytical separations are briefly discussed. Relative merits of SCW and other agents to treat the inner surfaces of fused silica capillaries are also mentioned.
Application of Mesoporous Carbon-Polymer Monolith for The Extraction of Phenolic Acid in Food Samples J. Chromatogr. A (IF 3.981) Pub Date : 2018-01-31 Yu-Ching Kuo, Wen-Qian Heish, Hsi-Ya Huang, Wan-Ling Liu
In this study, activated carbon-organic polymer (AC-polymer) extraction columns were prepared via microwave-assisted polymerization. The AC-polymer was applied in polymer monolith microextraction (PMME) of phenolic acids (PAs) in food samples. Structural characterization using Raman and Fourier transform infrared (FTIR) spectroscopy revealed the successful incorporation of AC into polymer monolith. In contrast to neat polymer in which low extraction efficiency (17.0∼ 57.7%) was observed, the AC-polymer (8 mg AC, 4 cm column length) afforded better extraction efficiency for PAs ranging from 75.8 to 99.8% for intra-day with less than 1.4% relative standard deviations (RSDs) and inter-day precision ranging from 74.3 to 100.1% (< 2.7% RSDs). The extraction efficiency for column-to-column were found to be in the range of 72.8 to 100.5% (<2.0% RSDs) (n = 3). Under the optimized conditions, the AC-polymer monolithic column was successfully applied in PMME of PAs in fruit wine and cranberry juice samples at concentrations of <4.8 mg L−1 and 26.54 mg L−1, respectively.
Macrocyclic Glycopeptide Chiral Selectors Bonded to Core-Shell Particles Enables Enantiopurity Analysis of the Entire Verubecestat Synthetic Route J. Chromatogr. A (IF 3.981) Pub Date : 2018-01-31 Chandan L. Barhate, Diego A. Lopez, Alexey A. Makarov, Xiaodong Bu, William J. Morris, Azzeddine Lekhal, Robert Hartman, Daniel W. Armstrong, Erik L. Regalado
Verubecestat is an inhibitor of β-site amyloid precursor protein cleaving enzyme 1 (BACE1) being evaluated in clinical trials for the treatment of Alzheimer’s disease. Synthetic route development involves diastereoselective transformations with a need for enantiomeric excess (ee) determination of each intermediate and final active pharmaceutical ingredient (API). The analytical technical package of validated methods relies on enantioselective SFC and RPLC separations using multiple 3 and 5 μm coated polysaccharide-based chiral stationary phases (CSPs) and mobile phases combinations. Evaluation of recently developed chiral columns revealed a single chiral selector (Teicoplanin) bonded to 2.7 μm core-shell particles using H3PO4 in H2O/ACN and triethylammonium acetate: methanol based eluents at different isocratic compositions allowed good enatioseparation of all verubecestat intermediates. EE determination of verubecestat is easily performed on NicoShell, another macrocyclic glycopeptide chiral selector bonded to 2.7 μm superficially porous particles. This approach enables fast and reliable enantiopurity analysis of the entire verubecestat synthetic route using only two of chiral columns and mobile phases on a conventional HPLC system, simplifying technical package preparation, method validation and transfer to manufacturing facilities.
Determination of free thyroid hormones in animal serum/plasma using ultrafiltration in combination with ultra-fast liquid chromatography-tandem mass spectrometry J. Chromatogr. A (IF 3.981) Pub Date : 2018-01-31 Rumi Tanoue, Imari Kume, Yasuo Yamamoto, Kohki Takaguchi, Kei Nomiyama, Shinsuke Tanabe, Tatsuya Kunisue
Thyroid hormones (THs), which mainly consist of 3, 3′, 5-triiodo-l-thyronine (T3) and L-thyroxine (T4), play a critical role in regulating biological processes such as growth and metabolism in various animal species. Thus, accurate measurement of T3 and T4, especially physiologically active free (protein-unbound) forms, in serum/plasma is needed for the evaluation of TH homeostasis. However, such high-precision determination of free THs is lacking for non-human species. The present study aimed to develop a highly sensitive and reliable liquid chromatography-tandem mass spectrometry (LC–MS/MS) method for the determination of six free THs in serum/plasma, which is applicable to not only humans but also non-human species. Two different physical separation steps, ultrafiltration (UF) and equilibrium dialysis (ED), were examined to obtain the free TH fraction. Several experimental conditions were carefully optimized and validated for UF or ED using the commercially available bovine serum. As a result, UF at 1100 × g and 37 °C for 30 min with a 30 kDa ultrafiltration device (Centrifree YM-30, Millipore) yielded excellent precision (CV: <10%). The optimized ED step also yielded high precision (CV: <10%) and the measurement values were approximately equal to those of UF, but at least 16 h were required to reach equilibrium. Thus, UF combined with LC–MS/MS was finally chosen, in terms of the time needed for the measurement. Acceptable accuracy (recovery: 70%–110%) and intra- and inter-day precision (CV: <10% and <12%, respectively) were obtained, when triplicate analyses in three different days were conducted using the bovine serum. The developed analytical method was successfully applied to the determination of free THs in serum/plasma samples of humans, cats, and dogs. Furthermore, comparison with free T4 concentrations measured by a common immunoassay method evidently indicated that the ultrafiltration-LC–MS/MS method developed in this study can increase the specificity and accuracy of TH measurement.
Determination of adsorbable organic halogens in surface water samples by combustion–microcoulometry versus combustion–ion chromatography titration J. Chromatogr. A (IF 3.981) Pub Date : 2018-01-31 Aziz Kinani, Hacène Salhi, Stéphane Bouchonnet, Said Kinani
Adsorbable Organic Halogen (AOX) is an analytical parameter of considerable interest since it allows to evaluate the amount of organohalogen disinfection by-products (OXBPs) present in a water sample. Halogen speciation of AOX into adsorbable organic chlorine, bromine and iodine, respectively AOCl, AOBr and AOI, is extremely important since it has been shown that iodinated and brominated organic by-products tend to be more toxic than their chlorinated analogues. Chemical speciation of AOX can be performed by combustion-ion chromatography (C-IC). In the present work, the effectiveness of the nitrate wash according to ISO 9562 standard method protocol to eliminate halide ions interferences was firstly examined. False positive AOX values were observed when chloride concentration exceeded 100 ppm. The improvements made to the washing protocol have eliminated chloride interference for concentrations up to 1000 ppm. A C-IC method for chemical speciation of AOX into AOCl, AOBr, and AOI has been developed and validated. The most important analytical parameters were investigated. The following optimal conditions were established: an aqueous solution containing 2.4 mM sodium bicarbonate/2.0 mM sodium carbonate, and 2% acetone (v/v) as mobile phase, 2 mL of aqueous sodium thiosulfate (500 ppm) as absorption solution, 0.2 mL min−1 as water inlet flow rate for hydropyrolysis, and 10 min as post-combustion time. The method was validated according to NF T90-210 standard method. Calibration curves fitted through a quadratic equation show coefficients of determination (r2) greater than 0.9998, and RSD less than 5%. The LOQs were 0.9, 4.3, and 5.7 μg L−1 Cl for AOCl, AOBr, and AOI, respectively. The accuracy, in terms of relative error, was within a ± 10% interval. The applicability of the validated method was demonstrated by the analysis of twenty four water samples from three rivers in France. The measurements reveals AOX amounts above 10 μg L−1 Cl in all untreated samples, suggesting the presence of organohalogen compounds in the sampled rivers. On weight concentration basis, AOCl accounted for 77–100% of AOX in the treated water samples. A good agreement between the conventional AOX method and the developed C-IC method was found.
Expanding the use of polymeric ionic liquids in headspace solid-phase microextraction: Determination of ultraviolet filters in water samples J. Chromatogr. A (IF 3.981) Pub Date : 2018-01-31 María J. Trujillo-Rodríguez, He Nan, Jared L. Anderson
Three crosslinked polymeric ionic liquid (PIL) sorbent coatings were used in headspace solid-phase microextraction for the determination of a group of ultraviolet filters. The developed crosslinked PIL-based materials include two polycations and a double confined PIL. The method, in combination with gas chromatography-mass spectrometry, is simple, solvent free, and does not require of any derivatization step. After proper optimization of the methodologies with each developed fiber, the analytical performance was compared with a commercial polyacrylate fiber. A study of the normalized calibration slopes, obtained by dividing the calibration slope of each analyte by the coating volume, revealed that the crosslinked fibers can be used as alternatives to commercial fibers for the determination of the selected group of compounds. In particular, the coating nature of the PIL containing the 1-vinylbenzyl-3-hexadecylimidazolium bis[(trifluoromethyl)sulfonyl]imide IL as monomer and the 1,12-di(3-vinylbenzylimidazolium)dodecane bis[(trifluoromethyl)sulfonyl]imide IL as crosslinker is the most suitable for the extraction of the selected compounds despite their coating volume, being 3.6 times lower than the commercial polyacrylate fiber. For this fiber, wide linear ranges, correlation coefficients higher than 0.990, limits of detection ranging from 2.8 ng L−1 to 26 ng L−1 and relative standard deviations ranging from 2.5 to 15% were achieved. Finally, all proposed PIL-based fibers were applied towards the analysis of tap water, pool water and lake water, with the majority of the ultraviolet filters being detected and quantified in the last two types of samples.
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