Establishment of the light-absorption ratio variation approach and application to determination of Co(ii) in the ng ml−1 level and novel characterization of Co(ii) and Zn(ii) complexes with 1,5-di(2-hydroxy-5-sulfophenyl)-3-cyanoformazan

Abstract

The light-absorption ratio variation approach (LARVA) has been established and applied to the determination of Co on the ng ml⁻¹ level with 1, 5-di(2-hydroxy-5-sulfophenyl)-3-cyanoformazan (DSPCF) at pH 9.33. Competitive replacement complexation (CRC) among DSPCF, Zn(II) and Co(II) as described was used to improve the analytical selectivity. The determination of the complex formation constants was also improved. Results have shown that ΔA_r⁻¹ (where ΔA_r is the light-absorption ratio variation) is linear in the range of Co(II) between 10 and 200 ng ml⁻¹. The limit of detection (3δ) of Co(II) is only 3.7 ng ml⁻¹. The combination of CRC and LARVA has been applied to the analysis of water quality with satisfactory results.