Electrochemical determination of hydroquinone using hydrophobic ionic liquid-type carbon paste electrodes

Hydroquinone (H2Q) is widely used in many fields such as reducing agent, antioxidant, polymerization inhibitor, black white film developer, anthraquinone dye, azo dyestuff and other chemical intermediate[1,2]. However, because of its toxicity to humans and difficulty in degradation, H2Q is also considered as a serious environmental pollutant[3]. Thus, it is very necessary to find simple and efficient analytical approaches for the determination of H2Q. Several analytical methods have been developed including high performance liquid chromatography[4,5], flow injection analysis[6], spectrophotometry[7-9], and electrochemistry[10,11] etc. In consideration of its good electrochemical activity, electro-oxidation of H2Q could be a competitive method for the determination of H2Q via recording electrochemical response[12-14].The carbon paste electrode (CPE), first introduced by Adams[15], is one of the most commonly used electrodes. Due to its low cost, ease of fabrication, high sensitivity and renewable surface, the CPE has been widely applied in the electroanalytical community. A traditional carbon paste electrode is composed of graphite powder and pasting liquids. Typical parameters required for pasting liquids are[16]: i) chemical inertness and electroinactivity, ii) high viscosity and low volatility, and iii) minimal solubility in aqueous solutions. Thus, the commonly used pasting liquids for the preparation of carbon paste were focused on organic mineral oils (e.g. nujol, paraffin)[17,18]. However, there exist two obvious disadvantages for mineral oil-type binders (or pasting liquids) since they are not component-fixed organic compounds. One is the presence of impurities that may give rise to undesirable effects on trace electroanalysis. The other is the inherent non-conductivity that can diminish the electrochemical sensitivity of the paste electrode. Therefore, the use of alternative viscous liquids with chemical inertness and inherent conductivity as a pasting binde