Study on the complex formation of anionic chelates of Co(II)–4-(2-thiazolylazo)resorcinol with ditetrazolium cations

The ion-associated complexes formed between anionic chelates of Co(II)–4-(2-thiazoly-lazo)resorcinol (TAR) and cations of ditetrazolium salts (DTS)—Nitro Blue Tetrazolium Chloride (NBT), Blue Tetrazolium chloride (BTC) and Neotetrazolium chloride (NTC)—in the liquid-liquid extraction system Co(II)–TAR–DTS–H2O–CHCl3 were studied. The optimum conditions for the formation and the solvent extraction of the ternary ion-associated complexes Co–TAR–DTS were found. The molar ratio of the components in the associates was determined by independent methods. Based on this, a reaction scheme and a general formula of the complexes were suggested. The extraction equilibria were investigated quantitatively. 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. Based on the obtained results and the lower price of the ditetrazolium salt BTC compared with NBT, the ion-associated complex of Co–TAR–BTC can be successfully used for determining of cobalt in alloys, biological, medical and pharmaceutical formulations.