Wednesday, November 4, 2009
Ballroom A+B (Camino Real Hotel)
The complex formation and liquid-liquid extraction in the vanadium(IV) - 4-(2-pyridylazo)-resorcinol (PAR) -ditetrazolium chloride i) 3,3'-(4,4'-biphenylene)-bis(2,5-diphenyl-2H-tetrazolium) chloride (Neotetrazolium chloride, NTC); ii) 3,3'-(3,3'-dimetoxy-4,4'-biphenylene)-bis(2,5-diphenyl-2H tetrazolium) chloride (Blue Tetrazolium chloride, BTC); and iii) 3,3'-(3,3'-dimetoxy-4,4'-biphenylene)-bis[2-(4-nitrophenyl)-5-phenyl-2H-tetrazolium] chloride (Nitro Blue Tetrazolium chloride, NBT)} - water - chloroform system has been studied. The molar absorptivitiy coefficients, composition of the complexes and constants of association (β) between the vanadium(IV) - PAR anionic chelates [VO(PAR)2]2- (I) and [VO(OH)2(PAR)2]4- (II), and ditetrazolium cations (DT2+) have been calculated. Some special features of NBT as an extraction-spectrophotometric reagent for vanadium(IV) have been discussed. In contrast to NTC and BTC which form associates with I and II, NBT forms associate only with II. The pH interval for maximum extraction of (NBT2+)2[VO(OH)2(PAR)2] is broader and allows work at lower pH values in comparison to the rest investigated ion-associates of V(IV,V)-PAR. That is why NBT is perspective for both - direct V(IV) determination and V(IV)/V(V) separation. Some additional characteristics for the V(IV)-PAR-NBT-water-chloroform system have been determined: extraction constant, distribution constant, recovery factor, limit of detection and limit of quantification. The Beer's law is valid up to 1.4 μg mL-1 vanadium(IV) with molar absorptivity coefficient of 3.55×104 L mol-1cm-1 at λmax=559 nm.