Autocatalytic decomposition of cobalt complexes as an indicator system for the determination of trace amounts of cobalt and effectors

Abstract

From theoretical considerations, the possibility of developing a constant sensitivity detection system for the determination of ultratrace levels of metal ions by the use of an autocatalytic degradation reaction of metal complexes was considered. The idea was realized by the use of the oxidative decomposition of the inert Co^III–2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenolate complex with peroxomonosulfate as oxidant and cobalt ion as catalyst. The inflection time of the absorbance–time curve is controlled by effectors such as cobalt(II) ion and ligands present in excess. Based on these properties, the system was successfully applied to the spectrophotometric determination of 10^–10 mol dm^–3 levels of cobalt ion and 10^–5 mol dm^–3 levels of effectors. The method does not require measurement of the rate constants.