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-(2thiazolylazo)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(TAR)2] –, and the tetrazoliumcation (Logb =4.7); the distribution of the ternary complex between the aqueous and organic phases (LogKD=0.88); and the extraction from water to chloroform (LogKex=Logb +LogKD=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.