Amperometric sensor based on MWNT and electropolymerized carminic acid for the simultaneous quantification of TBHQ and BHA

https://doi.org/10.1016/j.jelechem.2020.113885Get rights and content

Highlights

  • Poly(carminic acid) is presented as electrode surface modifier for the first time.

  • The conditions of carminic acid electropolymerization on MWNT/GCE are found.

  • Sensitive simultaneous quantification of TBHQ and BHA by DPV is developed.

  • Method is tested on the linseed oils.

Abstract

Amperometric sensor based on the layer-by-layer combination of multi-walled carbon nanotubes and electropolymerized carminic acid deposited on the glassy carbon electrode surface (poly(carminic acid)/MWNT/GCE) has been developed for the simultaneous quantification of tert-butylhydroquinone (TBHQ) and butylated hydroxyanisole (BHA). Conditions of poly(carminic acid) coverage obtaining have been found on the basis of TBHQ and BHA peak potential separation and oxidation currents. The best parameters have been observed for poly(carminic acid) electrodeposited from 50 μmol L−1 monomer solution by seven-fold cycling of potential in the range of 0.3–0.8 V with the scan rate of 50 mV s−1 in Britton-Robinson buffer (BRB) pH 2.0. Electrodes have been characterized by scanning electron microscopy (SEM) and electrochemical methods. Good resolution of TBHQ and BHA oxidation potentials equalled to 190 mV has been obtained on the poly(carminic acid)/MWNT/GCE vs. 146 mV on MWNT/GCE. The oxidation currents are 2.1- and 1.8-fold increased on polymer-modified electrode for TBHQ and BHA, respectively. Parameters of TBHQ and BHA electrooxidation on poly(carminic acid)/MWNT/GCE have been calculated. Sensor response is linear in the range of 0.50–75 μmol L−1 for TBHQ and 0.25–75 μmol L−1 for BHA with the limits of detection of 0.36 and 0.23 μmol L−1, respectively. Sensor selectivity in the presence of inorganic ions, ascorbic acid and α-tocopherol is confirmed. The sensor developed has been tested on the linseed oil. The recovery of 100–103% confirm high accuracy of the approach.

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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