SPECTROPHOTOMETRIC DETERMINATION OF COBALT(II) IN A LIQUID-LIQUID EXTRACTION SYSTEM CONTAINING 4-(2-THIAZOLYLAZO) RESORCINOL AND 2,3,5-TRIPHENYL-2H-TETRAZOLIUM CHLORIDE

The complex formation and a liquid-liquid extraction in the cobalt(II) - 4-(2- thiazolylazo)resorcinol (TAR) - 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) - water - chloroform system was studied. The optimum extractionspectrophotometric conditions were found. The molar ratio of the reacting species was determined to be 1:2:1 (Co:TAR:TTC). The following equilibrium processes were quantitatively examined: the association between the anionic chelate, [Co 3+ (TAR) 2 ] – , and the tetrazoliumcation (Logb =4.7); the distribution of the ternary complex between the aqueous and organic phases (LogK D =0.88); and the extraction from water to chloroform (LogK ex =Logb +LogK D =5.6). The effect of foreign ions and reagents on the extraction was studied. A sensitive (e 525 = 4.26×10 4 l mol –1 cm –1 ) and simple extraction-spectrophotometric procedure for cobalt determination was developed.