Amperometric sensor modified with nanomaterials for determination of hydroquinone in pharmaceutical samples

Abstract

Electrochemical sensors, devices capable of analyzing the electrochemical behavior of a system, appear as an alternative to conventional instrumental analytical techniques. Through changes in the environment in which they are inserted, these sensors will transform the electrical signal generated into a measurable signal proportional to the concentration of the analyte in solution. This generated signal can be evaluated through some electrochemical techniques, such as voltammetry, amperometry, impedimetry, conductometry and potentiometry. In order to improve the performance of electrochemical sensors, surface modification processes are carried out. Thus, in the first part, a theoretical review was carried out in order to elucidate concepts in the field of electrochemistry, as well as properties of the materials used as modifiers and their means of synthesis and treatments. In the second part, the objective was to develop an amperometric sensor modified with carbon nanotubes (CNT) and HY-type zeolite (ZEO-HY) for analysis of hydroquinone (HQ) in pharmaceutical products. In the second part of the work, first, voltammetric optimization studies were carried out regarding the composition of the modified carbon paste, reaching more favorable values of 20% of mineral oil, 30% of graphite powders, 30% of ZEO-HY and 20% NTC. Practical and theoretical studies were carried out regarding the contribution of the modifiers used, as well as the characterization of the developed material. For the analyzes of commercial samples containing HQ, amperometry in association with flow injection analysis (FIA) was chosen due to its greater sensitivity and better limit of detection (LD) and limit of quantification (LQ), repeatability and analytical frequency. For the amperometry-FIA optimization step, the parameters of work potential, flow rate and sampling loop volume were varied, and the best conditions were 0.1 V vs. Ag/AgCl, 4.69 mL min-1 and 65.0 μL, respectively. The calibration curve, constructed under the best operating conditions, presented a linear regression equation of i = 4.87925 x 10-8 + 0.00597 * C, with R = 0.997. A sampling rate of 100 injections per hour was achieved. The calculated LD was 2.69 x 10-7 mol L-1 and the LQ 8.99 x 10-7 mol L-1. For the repeatability study (n=15), using a solution of 6.0 x 10-5 mol L-1 HQ, the relative standard deviation (RSD) was 1.44%. The pharmaceutical samples analyzed showed results in agreement with those values found on the labels of the creams, as well as the High-Performance Liquid Chromatography (comparative technique).