Simultaneous Determination of Ferulic Acid and Vanillin in Vanilla Extracts Using Voltammetric Sensor Based on Electropolymerized Bromocresol Purple

Abstract

Natural phenolic antioxidants are one of the widely studied compounds in life sciences due to their important role in oxidative stress prevention and repair. The structural similarity of these antioxidants and their simultaneous presence in the plant samples stipulate the development of methods for their quantification. The current work deals with the simultaneous determination of vanillin and its bioprecursor ferulic acid using a voltammetric sensor for the first time. A sensor based on the layer-by-layer deposition of the polyaminobenzene sulfonic acid functionalized single-walled carbon nanotubes (f-SWCNTs) and electropolymerized bromocresol purple has been developed for this purpose. The best response of co-existing target analytes was registered for the polymer obtained from the 25 µM dye by 10-fold potential cycling from 0.0 to 1.2 V with the scan rate of 100 mV s−1 in 0.1 M phosphate buffer (PB), pH 7.0. Scanning electron microscopy (SEM), cyclic voltammetry and electrochemical impedance spectroscopy (EIS) confirmed the effectivity of the sensor developed. The linear dynamic ranges of 0.10–5.0 µM and 5.0–25 µM for both analytes with the detection limits of 72 nM and 64 nM for ferulic acid and vanillin, respectively, were achieved in differential pulse mode. The sensor was applied for the analysis of vanilla extracts.

Electrode Based on the MWCNTs and Electropolymerized Thymolphthalein for the Voltammetric Determination of Total Isopropylmethylphenols in Spices

“…The polythymolphthalein-modified electrode is characterized by the lowest electron transfer resistance among the electrodes under consideration that agree with cyclic voltammetry data. Similar behavior has been reported for the poly(bromocresol purple)-modified electrode [ 61 ]. The impedance spectra fitting has been carried out using Randles’ equivalent circuits ( Table 1 ).…”

“…This process is confirmed by the CVs on the second and subsequent scans at which a significant decrease in the dye oxidation currents has been observed. Thus, thymolphthalein electropolymerization proceeds with the formation of non-conductive coverage that is typical behavior for the phenolic monomers [ 54 , 63 ] including triphenylmethane dyes such as aluminon [ 58 ], pyrocatechol violet [ 60 ], bromocresol purple [ 61 ].…”

“…Further development in the field of polymer-modified electrodes for the isopropylmethylphenols can be focused on the application of polymeric coverages based on the electropolymerized dyes. Recently, electrodes based on the electropolymerized azo [ 57 ] and triphenylmethane dyes [ 58 , 59 , 60 , 61 ] have been developed for the determination of phenolic acids and flavonoids. Triphenylmethane dyes containing phenolic fragments form non-conductive polymers.…”

“…Triphenylmethane dyes containing phenolic fragments form non-conductive polymers. Therefore, the electropolymerization of these dyes has been carried out at the surface of the electrodes modified with carbon nanomaterials [ 58 , 59 , 60 , 61 ], which provide sufficient conductivity of the electrode and high surface area available for the electrodeposition of polymer.…”

Electrochemical Characterization of the Antioxidant Properties of Medicinal Plants and Products: A Review

“…Electrode fouling often occurs due to the complex composition of the plant sample that requires renewal of the electrode surface after each measurement [145,147,151,156,157,173,185]. Single-use electrodes, in particular screen-printed ones, are a good alternative to electrode cleaning after each measurement.…”