Catalytic determination of cobalt at sub-nanogram levels using the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline by manual and flow-injection methods

摘要

A catalytic photometric method was developed for the determination of sub-nanogram levels of cobalt. The method is based on the catalytic effect of cobalt(II) on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (DAOS) to form a colored dye (#lambda#_(max) = 525 nm) in the presence of hydrogen peroxide. In this reaction system, 1,2-dihydroxybenzene-3,5-disulfonate (Tiron) acted as an effective activator for the catalysis of cobalt(II). Variation of reaction time between 5 and 10 min allows the determination range to be extended from 0.01 to 1.0 ng ml~(-1). The reaction system can also be successfully adapted to flow-injection analysis (FIA). The dynamic range of the proposed flow-injection method was 0.01-1.0 ng ml~(-1) and detection limit (signaloise, S/N = 3) was 5 pg ml~(-1) at a sampling rate of 30 h~(-1). Manual and flow-injection methods were applied to the direct determination of cobalt in pepperbush as a standard material.