Fused-silica capillary internally modified with nanostructured octadecyl silica for dynamic in-tube solid-phase microextraction of polycyclic aromatic hydrocarbons from aqueous media

https://doi.org/10.1016/j.microc.2020.104672Get rights and content

Highlights

  • Inner walls of a silica capillary were coated with spherical silica nanoparticles.

  • The surface of the silica nanoparticles was then modified with ODS chains.

  • So, a porous, effective and robust sorbent for IT-SPME sampling was developed.

  • The modification was conducted using a simple and green nucleosynthesis procedure.

  • The developed IT-SPME-GC-FID was employed for analysis of PAHs in polluted waters.

Abstract

The internal surface of a fused-silica capillary was made much more porous, more adsorptive and resistant to chemical and mechanical stresses by chemical coating using nanostructured octadecyl silica particles. The modification process was conducted using a simple and green nucleosynthesis procedure. The internally modified capillary was used as an in-tube solid-phase microextraction (IT-SPME) device for the extraction and preconcentration of ultratrace levels of polycyclic aromatic hydrocarbons (PAHs) in aqueous samples, followed by determination using gas chromatography-flame ionization detection (GC-FID) system. Morphology and structure of the sorbent was characterized by FT-IR, SEM and energy dispersive X-ray techniques. The effects of a range of experimental variables on the efficiency of the IT-SPME-GC-FID method were evaluated and optimized. Under the optimal conditions, good linearity (R2 > 0.99) was obtained for the calibration graphs over the range of 1–4000 ng mL−1. Detection limits were 0.22–0.47 ng mL−1 and relative standard deviations were obtained in the range 4.4–10.3%. Recoveries of the spiked samples were found to be 78.7–103.5%. The proposed IT-SPME-GC-FID strategy was applied successfully for the analysis of PAHs in real water samples. The results demonstrated good analytical performances, compared with those reported elsewhere for the sampling and quantification of PAHs in aqueous media.

Introduction

Silica is plentiful natural material that can be obtained at low-cost and processed easily for preparation of a range of useful forms. It has widespread applications in electronics, separation sciences and chromatography. It has gained a commercial trading turnover of billions of dollars [1,2]. Different silica composites and nanocomposites have been studied extensively due to their remarkable-combined features [3]. Nonetheless, there are few published reports about the reconstituted forms of silica, which is not in balance with the importance and widespread uses of this valuable natural material. Nowadays, development of novel and reconstituted forms of silica is a challenging pursuit in separation sciences. One of the most useful silica bonded-phase materials is octadecyl silica (ODS), which has widespread applications in separation science, especially in the preparation of chromatographic columns and solid-phase extraction (SPE) sorbents [4]. In recent years, great interest has been focused on the development of new nanostructures of different materials [5]. However, literature surveys show that there is only a small number of publications concerning nano-ODS.

Solid-phase microextraction (SPME) is a green solvent-free sample pretreatment strategy that was introduced in 1990 to address the drawbacks of the traditional extraction techniques [6]. A range of SPME configurations, including fiber-based and needle-based approaches have emerged. Regular fiber-SPME [7], solid-phase dynamic extraction (SPDE) [8], stir bar sorptive extraction (SBSE) [9], and headspace sorptive extraction (HSSE) [10] have been introduced as fiber-based methods. However, due to the practical limitations associated with the coated fibers, needle-based techniques such as needle trap device (NTD) [11], in-needle coated fiber (INCF) [12], inside-needle capillary adsorption trap (INCAT) [13], and in-tube SPME (IT-SPME) [14] have been developed. IT-SPME, first introduced by Pawliszyn et al. in 1997 [15], uses a piece of capillary coated (internally) with a polymeric sorbent for trapping of analytes by passing the sample through the capillary [15]. Feasibility of simple on-line coupling to liquid chromatography (LC) and resistance to LC mobile phases can be considered as the most prominent features of IT-SPME, while these factors being the important limitations of other SPME configurations. It is particularly promising to couple IT-SPME to growing techniques of microcolumn liquid chromatography, capillary liquid chromatography and capillary electrophoresis. This characteristic makes it the most efficient SPME technique for sampling highly polar compounds in aqueous media [16].

IT-SPME is usually performed in flow-through or cycle-mode [17]. In the flow-through mode the sample is passed through the capillary in one direction, while in the cycle mode the sample is iteratively drawn and ejected, in two flow directions. For on-line coupling of IT-SPME to the LC instrument different arrangements of IT-SPME interfaced with a multiport-valve can be used. The general configuration to perform the flow-through mode is to replace the sample loop of a six-port rotary injection valve with the IT-SPME capillary. Accordingly, this mode is sometimes called in-valve SPME. The most commonly used form is an open-tubular capillary that the sorbent coated on its inner wall. This type of IT-SPME is also the best choice for coupling to a GC instrument. Over 60% of the IT-SPME reports have employed commercial fused-silica open-tubular (FSOT) capillaries, while about 40% have used porous-layer open-tubular (PLOT) columns, which have larger surface areas. Fiber-, wire- and sorbent-packed IT-SPME that have been developed over recent years are less frequently used versions [18], [19], [20].

A fascinating aspect of IT-SPME is the use of custom-made capillaries with controlled sorption properties, especially by employing newly developed nanosorbents [21]. IT-SPME capillaries with nanomaterial sorbents can be prepared using electrodeposition, liquid-phase deposition, and sol-gel processes [22]. In this way, different IT-SPME systems have been prepared by coating commercially available fused-silica capillaries with polydimethylsiloxane (PDMS) and polyethylene glycol (PEG)-based phases and used to extract polar herbicides in aqueous media [23]. The results were compared with those obtained with tetraethyl orthosilicate trimethoxyethylsilane polymer, and a similar polymer, reinforced with silica nanoparticles. Li et al. prepared an IT-SPME setup by deposition of a liquid-phase of silica nanoparticles on the inner walls of a capillary, before modification by octadecyl groups. It was coupled with high-performance liquid chromatography with UV detection (HPLC–UV) and applied to the determination of endocrine disruptors and PAHs, as model analytes. The nanoparticle phase showed higher extraction capacity compared with an octadecyl-grafted capillary and an octadecyl-grafted silica-coated capillary [24]. Tang et al. reported a review article for preparation, drug delivery features, and biocompatibility of mesoporous silica nanoparticles )MSNs) in 2012 [25]. In that report, the synthesis methods for preparation of ordered MSNs and hollow/rattle-type MSNs were discussed. Additionally, in-vivo and in-vitro biotranslocation and biocompatibility of MSNs were surveyed by considering their physicochemical properties.

Laaks et al. developed an in-tube extraction (ITE) device for headspace sampling of 2-methylisoborneol, benzene, toluene, ethylbenzene, xylenes, halogenated hydrocarbons, fuel oxygenates, and geosmin in drinking water. The separation and measurement of the analytes were carried out by GC–MS. Different single- and mixed-bed traps were prepared using commercially available sorbents and compared for their extraction efficiencies [26]. In further research, Pawliszyn et al. synthesized a molecularly imprinted polymer sorbent for automated IT-SPME analysis of propranolol in serum samples [27]. This research group used a restricted access material (alkyl-diol-silica) as a biocompatible sorbent, for off-line and automated ITE of benzodiazepines in biological fluids. They took advantage of bifunctionality of the sorbent to prevent the sorption of proteins and thereby to inhibit contamination of the ITE capillary [28]. An ITE setup was fabricated by coating the internal surface of a fused-silica capillary by β-cyclodextrin (β-CD) using a sol-gel method. The capillary was joined to a PEEK pre-extraction tube and coupled with HPLC for on-line quantification of ibuprofen, ketoprofen, and fenbufen [29]. Different aspects of development and application of capillary microextraction and automated IT-SPME techniques, including clinical, environmental, food, and forensic analyses were overviewed by Kataoka et al. in two review reports [16,30]. Fernández-Amado et al. evaluated different strengths and weaknesses of IT-SPME in a scoping review article [17].

The above discussion demonstrates that a major feature of IT-SPME is easy preparation of a low-cost, high-capacity, uniform, and efficient capillary, which complies with the green chemistry principles. On the other hand, the stability and capacity of the IT-SPME capillary is limited by the coated amount of sorbent. Therefore, the prime aim is to prepare a chemically and mechanically stable, highly porous, and high surface area sorbent. In the present research, the inner wall of a fused-silica GC capillary column was modified with spherical nano-silica particles, using a rapid and simple nucleation process. Next, octadecyl groups were bonded chemically to the surface of the nano-silica particles to increase the surface area and to provide a durable brush-like covalently bonded ODS chains for trapping analyte molecules. The developed IT-SPME sorbent was then utilized for extraction and preconcentration of PAHs from aqueous media followed by GC-FID quantification.

Section snippets

Reagents and solutions

Anthracene (Ant), acenaphthene (Ace), fluoranthene (Flt), fluorene (Fln), naphthalene (Nap), pyrene (Pyr) and phenanthrene (Phe), all with purities > 99%, were purchased from Merck (Darmstadt, Germany). Concentrated ammonia solution 25% was from the same supplier. The working standard solutions were prepared weekly by serial diluting of the stock with methanol. All stock and working standard solutions were kept in a refrigerator. Trichloro-octadecyl silane (TCODS, ≥ 90%) and tetraethyl

Characterization of the prepared nano-ODS sorbent

FT-IR spectra were recorded to characterize the synthesized sorbent and identify the functional groups in its structure. As shown in Fig. S1, absorption bands at 3410, 2924, 1464, 952, and 801 cm−1 are related to the vibrations of Osingle bondH, Csingle bondH, Sisingle bondC, Sisingle bondOsingle bondH, and Sisingle bondOsingle bondSi bonds, respectively. This means that the octadecyl chains have been bonded to the silica substrate.

To visualize differences between the regular fused-silica capillary and the modified capillary, each was photographed using a probe-type USB

Conclusions and future trends

Based on the wide applications of silica and ODS, in this research a more efficient nano-ODS sorbent has been developed. For this purpose, the internal surface of a regular fused-silica capillary was coated with spherical silica nanoparticles and the surface of the silica nanoparticles then modified with octadecyl chains. This arrangement provided a robust and efficient nano-ODS sorbent. The modified capillary was characterized and utilized for IT-SPME sampling of PAHs in water samples followed

CRediT authorship contribution statement

Fardin Harati: Data curation, Writing - original draft. Alireza Ghiasvand: Supervision, Conceptualization, Methodology, Visualization. Kolsoum Dalvand: Software, Validation. Paul R. Haddad: Writing - review & editing.

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgment

The authors are grateful for the support of Lorestan University.

References (41)

  • Y. Fan et al.

    In-tube solid phase microextraction using a β-cyclodextrin coated capillary coupled to high performance liquid chromatography for determination of non-steroidal anti-inflammatory drugs in urine samples

    Talanta

    (2005)
  • H. Kataoka et al.

    Developments and applications of capillary microextraction techniques: a review

    Anal. Chim. Acta

    (2009)
  • Q.-W. Yu et al.

    Temperature-response polymer coating for in-tube solid-phase microextraction coupled to high-performance liquid chromatography

    Talanta

    (2011)
  • S.A. Kulkarni et al.

    Tuning the hydrophobic properties of silica particles by surface silanization using mixed self-assembled monolayers

    J. Colloid Interf. Sci.

    (2008)
  • S.A. Kulkarni et al.

    Thermal stability of self-assembled octadecyltrichlorosilane monolayers on planar and curved silica surfaces

    Thin Solid Films

    (2006)
  • M.A. Bezerra et al.

    Response surface methodology (RSM) as a tool for optimization in analytical chemistry

    Talanta

    (2008)
  • J. Feng et al.

    Polydopamine supported preparation method for solid-phase microextraction coatings on stainless steel wire

    J. Chromatogr. A

    (2011)
  • K. Li et al.

    Solid-phase extraction with C30 bonded silica for analysis of polycyclic aromatic hydrocarbons in airborne particulate matters by gas chromatography–mass spectrometry

    J. Chromatogr. A

    (2007)
  • F. Busetti et al.

    Determination of sixteen polycyclic aromatic hydrocarbons in aqueous and solid samples from an Italian wastewater treatment plant

    J. Chromatogr. A

    (2006)
  • M.-C. Wei et al.

    Determination of polycyclic aromatic hydrocarbons in aqueous samples by microwave assisted headspace solid-phase microextraction and gas chromatography/flame ionization detection

    Talanta

    (2007)
  • Cited by (0)

    View full text