Amperometric sensor based on MWNT and electropolymerized carminic acid for the simultaneous quantification of TBHQ and BHA
Graphical abstract
Introduction
Food antioxidant additives represent an important class of compounds that are widely used in food technology in order to improve the foodstuff characteristics (the storage parameters, color and flavor, the nutritional value, possible health effect and so on) [1]. Synthetic antioxidants in particular phenolic ones are usually applied for the oily and fatty products to prevent oxidative processes caused by lipid peroxidation [2]. The most common preserving additives are sterically hindered phenols tert-butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA) and butylated hydroxytoluene. Their contents in foodstuff is strictly regulated [3,4] as far as high concentrations lead to negative health effects like chronic neurotoxic effects and vision disturbances [5], carcinogenesis [6], underdevelopment of the reproductive system [7]. The toxicity of TBHQ, BHA and butylated hydroxytoluene is different [1,2]. The mixtures of additives are applied as well and the level of their total contents is varied. Summarizing the mentioned above, the sensitive and selective methods for the simultaneous determination of TBHQ and BHA are required.
Taking into account the complex matrix of foodstuff, different types of chromatography are usually applied for simultaneous quantification of TBHQ and BHA. For example, high-performance liquid chromatography with UV- [[8], [9], [10], [11], [12]] and chemiluminescent [13] detection or gas chromatography with flame ionization [14] or mass-spectrometric detection [[15], [16], [17]]. However, these approaches require high purity solvents, a range of preliminary steps during sample preparation, time-consuming measurements, expensive equipment and high professional skills of the staff.
These limitations are successfully overcome using electrochemical methods. TBHQ and BHA are oxidized under conditions of voltammetry that is widely used for their quantification. Traditional carbon-based or platinum electrodes show overlapped TBHQ and BHA oxidation peaks and usually can not be applied for their simultaneous determination using voltammetry. Flow-injection analysis with pulse amperometric detection on glassy carbon electrode (GCE) allows simultaneous determination of TBHQ and BHA [18,19]. As for the voltammetric methods, there are three ways to solve this problem. The first one is usage of surfactant-based media leading to the shift and resolution of the oxidation peaks of TBHQ and BHA [[20], [21], [22]]. The second approach is application of chemometric treatment of voltammetric data obtained allowing analytes quantification in three- and four-component mixtures [[23], [24], [25]]. And the third trend is fabrication of a wide range of chemically modified electrodes. Metal and metal oxide nanoparticles, carbon nanomaterials, polymers and their different combinations are typically applied [[26], [27], [28], [29], [30], [31], [32], [33], [34], [35]]. The corresponding analytical characteristics are presented in Table 1. It should be noted, that there is just one example of the electrode modified with polymeric material for the simultaneous determination of TBHQ and BHA [35]. Moreover, the molecularly imprinting technique has been used for TBHQ selective recognition. However, the analytical characteristics achieved can be further improved.
In present work, novel sensor based on the layer-by-layer combination of multi-walled carbon nanotubes (MWNT) and electrochemically polymerized carminic acid has been developed for the simultaneous determination of TBHQ and BHA. Carminic acid has been used as a monomer for the first time. The conditions of electropolymerization providing the best response of TBHQ and BHA mixture have been found. The sensor created is characterized by high effective surface area and statistically significant increase of electron transfer rate in comparison to MWNT/GCE providing improvement of TBHQ and BHA response.
Section snippets
Reagents and chemicals
TBHQ of 97% purity, BHA (98%) and carminic acid were obtained from Aldrich (Germany). Their 10 mmol L−1 stock solutions were prepared by dissolving of definite amount in 5.0 mL of distilled water (for carminic acid) or ethanol rectificate (for TBHQ and BHA). Less concentrated solutions of TBHQ and BHA were prepared by exact dilution with ethanol in 5.0 mL volumetric flasks before measurements.
Stock solutions of 99% l-ascorbic acid (Sigma, Germany) and 96% α-tocopherol (Sigma-Aldrich, Germany)
Voltammetric characteristics of TBHQ and BHA on GCE and MWNT/GCE
Voltammetric behavior of TBHQ and BHA and their mixture has been studied on the bare GCE and MWNT/GCE in BRB pH 2.0 under conditions of DPV. Both analytes are oxidized on GCE at 0.501 and 0.594 V for TBHQ and BHA, respectively (Fig. 1a, curves 1 and 2). Peaks potential separation of 93 mV does not allow simultaneous detection as far as oxidation peaks overlapping is observed (Fig. 1a, curve 3). Therefore, MWNT/GCE has been used for further investigations. Cathodic shifts of oxidation potentials
Conclusions
Novel sensitive and selective amperometric sensor has been developed for the simultaneous determination of TBHQ and BHA. Combination of MWNT with electropolymerized carminic acid as a sensitive layer provides significant increase of the electrode effective surface area and electron transfer rate leading to improvements in the response of TBHQ and BHA and good resolution of their oxidation peaks at simultaneous presence. The calibration graphs obtained for equimolar mixtures can be applied for
CRediT authorship contribution statement
Guzel Ziyatdinova: Conceptualization, Methodology, Investigation, Writing - original draft, Writing - review & editing, Visualization, Supervision. Ekaterina Guss: Methodology, Investigation, Validation, Formal analysis, Funding acquisition. Herman Budnikov: Conceptualization, Writing - original draft.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The financial support of Russian Foundation for Basic Research (grant 18-33-00220-mol_a) is gratefully acknowledged. Authors thank Yuri Osin and Vyacheslav Vorobev (Interdisciplinary Center for Analytical Microscopy, Kazan Federal University) for the SEM measurements.
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