Vanadium (IV and V) speciation with a catechol derivative and tetrazolium salt

The possibility of application of 4-nitrocatechol (4-NC) - tetrazolium salt - organic solventsystems for liquid-liquid extraction-spectrophotometric vanadium (IV and V) speciation wasstudied. 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)) andthree organic solvents (chloroform, 1,2-dichloroethane, 1-butanol) were tested in this study. Thebest results were obtained with MTT and chloroform. A direct, very simple, fast and sensitiveprocedure for vanadium (IV and V) speciation based on the spectral differences of the extractedternary complexes of V(IV) and V(V) was developed. It was found that the optimization of theMTT to 4-NC ratio has a key role in the speciation results. At deficiency of 4-NC towards MTTthe vanadium(IV) complex absorbed light at 390 and 570 nm, while the V(V) complex absorbedonly at 390 nm. The corresponding molar absorptivities were calculated to be εV(IV)390 = 3.6×104L mol-1 cm-1, εV(IV)570 = 1.7×104 L mol-1 cm-1 and εV(V)390 = 3.1×104 L mol-1 cm-1. The methodwas applied for vanadium (IV and V) speciation in industrial samples with low Fe and Alcontent (catalyst for oxidation of SO2) and good results were obtained in terms of precision andaccuracy.