The electrochemical oxidation of 4-NITROCATECHOL in aqueous media was studied using cyclic voltammetry. The results indicate that the stability of electrochemically generated o-nitrobenzoquinone is low and decreases with increasing pH. Also, our voltammetric data show that the species produced from the conversion of o-nitrobenzoquinone are electro-inactive in the studied potential range. In addition, the results reveal that the rate of conversion of o-nitrobenzoquinone is dependent on the nature of the solvent. According to EC mechanism, the observed homogeneous rate constant of the conversion of o-nitrobenzoquinone was estimated by comparing the experimental cyclic voltammograms with the digitally simulated results. Finally, a possible mechanism is proposed for the electrode process, on the basis of the present and previous investigations.

The possibility of application of 4-NITROCATECHOL (4-NC) - tetrazolium salt -organic solvent systems for liquid-liquid extraction-spectrophotometric vanadium (IV and V) speciation was studied. Six commercially available tetrazolium salts (2, 3, 5-triphenyltetrazolium chloride (TTC), 3- (2-naphtyl) -2, 5-diphenyltetrazolium chloride (Tetrazolium Violet, TV); 3- (4, 5-dimethyl-2-thiazol) -2, 5-diphenyltetrazolium bromide (Thiazolyl Blue Tetrazolium, MTT), 2- (4-iodophenyl) -3- (4-nitrophenyl) -5-phenyltetrazolium chloride (INT), 3, 3’- (4, 4’-biphenylene) bis (2, 5-diphenyltetrazolium) chloride (Neotetrazolium chloride, NTC) and 3, 3’- [3, 3’-Dimetoxy (1, 1’-biphenyl) -4, 4’-diyl] bis (2, 5-diphenyltetrazolium) chloride (Blue Tetrazolium chloride, BTC)) and three organic solvents (chloroform, 1, 2-dichloroethane, 1-butanol) were tested in this study. The best results were obtained with MTT and chloroform. A direct, very simple, fast and sensitive procedure for vanadium (IV and V) speciation based on the spectral differences of the extracted ternary complexes of V (IV) and V (V) was developed. It was found that the optimization of the MTT to 4-NC ratio has a key role in the speciation results. At deficiency of 4-NC towards MTT the vanadium (IV) complex absorbed light at 390 and 570 nm, while the V (V) complex absorbed only at 390 nm. The corresponding molar absorptivities were calculated to be eV (IV) 390=3.6 ´ 104 L mol-1 cm-1,  eV (IV) 570 =1.7 ´ 104 L mol-1 cm-1 and eV (V) 390=3.1 ´ 104 L mol-1 cm-1. The method was applied for vanadium (IV and V) speciation in industrial samples with low Fe and Al content (catalyst for oxidation of SO2) and good results were obtained in terms of precision and accuracy.