RESUMO
The formation of ternary ion-association complexes of Co(II) with 4-(2-pyridylazo)resorcinol (PAR) and tetrazolium salts (TS) - (3-(4,5-dimethylThiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and 3-(2-naphtyl)-2,5-diphenyl-2H-tetrazolium chloride (TV) - were investigated with the aid of the extraction-spectrophotometric method. The optimum conditions for the extraction of Co(II) were found. On the basis of the experimental data and their mathematical treatment the association process in aqueous phase and extraction process was investigated quantitatively. The molar ratios of the components in the associates were determined. The results show that the extracted species could be represented with the general formula (TS)[CoH(PAR)(2)]. The following key constants were calculated: association constant, distribution constant, extraction constant and recovery factor. The validity of Beer's law was checked and some analytical characteristics were calculated.
RESUMO
The formation and liquid-liquid extraction of ion-association complexes between gallium(III)-4-(2-pyridylazo)resorcinol (PAR) anionic chelates and cations of four ditetrazolium chlorides (DT2+) were studied: Neotetrazolium chloride (NTC), Blue Tetrazolium chloride (BTC), Nitro Blue Tetrazolium chloride (NBT) and Tetranitro Blue Tetrazolium chloride (TNBT). The optimum extraction-spectrophotometric conditions, composition of the extracted species {1:2:1 and/or 1:2:2 (Ga:PAR:DT)}, some equilibrium constants {constants of association (beta), constants of distribution (KD and constants of extraction (Kex)} and analytical characteristics {molar absorptivity (epsilon), Sandell's sensitivity, intervals of adherence to Beer's law, etc.} were found. Relationships involving the number of nitro groups in DT2+ (Nnitro; DT2+ = BT2+, NBT2+ and TNBT2+) or molecular mass of DT2+ (MM; DT2+ = NT2+ and BT2+) were discussed: Log beta =f(Nnitro), Log KD =f(Nnitro), Log Kepsilon=f(Nnitro), Log epsilon =f(Nnitro) and Log beta = f(Log MM).
