Simultaneous differential kinetic determination of cobalt and nickel based on on-line complex formation and ligand substitution reaction using a stopped-flow FIA system

Abstract

A differential kinetic method utilizing a stopped-flow FIA system is proposed for the simultaneous determination of cobalt and nickel at sub-ppm levels in mixtures. The method is based on the large difference in the rates of the ligand substitution reaction of the metal complexes of 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)aniline (PSAA) with nitrilotriacetic acid. The apparent reaction rate for the Ni-PSAA complex is more than 100 times larger than that for Co-PSAA complex. The relative standard deviations in the analysis of binary mixture of 0.50 μg/ml cobalt and 0.30 μg/ml nickel were 1.9% and 2.1%, respectively (n=7). The sample throughput is about 20 h⁻¹. The effect of various ions was also studied. The proposed method has satisfactorily been applied to synthetic samples containing different ratios of cobalt and nickel 1/12 to 10/1.