Shipboard determination of dissolved cobalt in sea-water using flow injection with catalytic spectrophotometric detection

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Abstract
A flow injection spectrophotometric technique for the determination of cobalt in sea-water and hydrothermal sea-water solutions is described. It is based on the catalytic effect of cobalt(II) on the oxidation of N,N′-diethyl-p-phenylenediamine by hydrogen peroxide in the presence of Tiron as an activator. The catalytic activity of cobalt(II) was found to be significantly enhanced by the presence of sea-water matrix components, especially calcium ions, improving the sensitivity of cobalt determination in sea-water. The comparatively weak basic medium (pH 8.7–9.0) of the reaction and its relative freedom from co-existing ions allowed the direct analysis of sea-water to be conducted effectively without any preliminary steps. The sampling rate was 50 h–1. The limit of detection for cobalt was 1 ng l–1 and the relative standard deviation at the level of 10–100 ng l–1 was 2–8%(n= 5). The technique was confirmed to be accurate on the basis of the analysis of the standard sea-water solutions CASS-2 and NASS-2. Artificial hydrothermal solution samples were analysed by the proposed technique and the results were in good agreement with data obtained by ICP-MS.

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