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

Abstract

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