SPECTROPHOTOMETRIC DETERMINATION OF COBALT BY EXTRACTION OF ITS N-HYDROXY-N,N-DIPHENYLBENZAMIDINE COMPLEX

Cobalt(II) was found to react with N-1-hydroxy-N-1,N-2-diphenylbenzami dine to form a 1:3 metal to ligand complex. The yellow brown complex w as quantitatively extracted into toluene from the aqueous phase at pH 7.5-9.5. The coloured system obeyed Beer's law in the concentration ra nge 0.1-12 mu g ml(-1) of cobalt at 405 nm. The effects of experimenta l variables and of several foreign ions on the determination of cobalt (II) have been studied and the method has been found to be precise and highly selective. The molar absorptivity equals to 7.0x10(3) l mol(-1 ) cm(-1). The method has been applied successfully to the determinatio n of cobalt in steels and vitamin B-12.