Poly-ethylenedioxypyrrole (PEDOP) coated thiolated multiwall carbon nanotubes palladium nanoparticles (MWCNTs-Pd) modified glassy carbon electrode (GCE) [PEDOP/MWCNTs-Pd/GCE] for the determination of hydroquinone (HQ) and it's isomer catechol (CA) were synthesized and compared with bare GCE and thiolated multiwall carbon nanotubes (MWCNTs-SH/GCE). The modification could be made by simple processes on a GCE with MWCNTs-Pd covered by PEDOP in a 0.05 M tetrabutylammonium perchlorate (TBAP)/MeCN solution system. A well-defined peak potential evaluation of the oxidation of hydroquinone to quinone at 0.05 V (vs. Ag/AgCl), and electrochemical reduction back to hydroquinone were found by cyclic voltammetry (CV) in phosphate buffered saline (PBS) at pH 7.4. Peak current values increased linearly with increasing hydroquinone contents. The peak separation between the anodic and cathodic peaks at the PEDOP/ MWCNTs-Pd/GCE was ΔEp = 40 mV for HQ and ΔEp = 70 mV for CA, resulting in a higher electron transfer rate. Moreover, good reproducibility, excellent storage stability, a wide linear range (0.1 µM -5 mM for HQ and 0.01 µM -6 mM for CA), and low detection limits (2.9 × 10 −8 M for HQ and 2.6 × 10 −8 M for CA; S/N = 3) were determined using differential pulse voltammetry (DPV) and amperometric responses; this makes it a promising candidate as a sensor for determination of HQ and CA.Key Words : Hydroquinone, Catechol, Electrochemical sensor, Carbon nanotubes, MWCNTs-palladium nanoparticles
IntroductionSince its introduction for clinical use in 1961, hydroquinone (HQ; 1,4-dihydroxybenzene) has been a popular depigmenting agent, inhibiting melanin formation.1,2 Accordingly, it has been used not only in cosmetic creams and tanning but also pesticides, flavoring agents, medicines, photography chemicals, organic constituent of tobacco smoke, and widely distributed throughout nature.3-6 Nevertheless, HQ and its isomers, catechol (CA; 1,2-dihydroxybenzene) and resorcinol (RE; 1,3-dihydroxybenzene), are harmful to both humans and animals, even at low concentrations, and they are difficult to degrade due to their coexistence and interference during determination.7-10 Moreover, they are considered to be environmental pollutants by the United States Environmental Protection Agency (EPA) and the European Union (EU) and banned its use in cosmetics and such formulations.11 But some researchers have acknowledged that these dihydroxybenzenes not only affect activities of some enzymes, but also have biological importances such as antioxidation and antivirus characterestics, thus are environmentally significant as antioxidants and antiviral agents.12 Therefore, various methods for their determination have been carried out by spectrophotometric and chromatographic techniques.13-15 Unfortunately they possess high cost and low sensitivity, require complicated pretreatments, and consume much time. So, it's demanding to develop simple, rapid, and electrochemical methods with low cost, high sensitivity, and ease of operation. 16,17 From previous re...