Using silica modified by poly(hexamethylene guanidine) and nitroso-R-salt for the preconcentration and determination of cobalt

An adsorbent based on silica consecutively modified with poly(hexamethylene guanidine) and nitroso-R-salt is proposed for the adsorption preconcentration and photometric determination of cobalt. The approach gives adsorbents with the controlled surface concentration of the reagent. The adsorbent extracts cobalt(II) from solutions of pH 5-9 with partition coefficients of 5x10(3)-1 x 10(4) cm(3)/g. The specific features of the influence of Fe(II) and Fe(III) on the preconcentration and determination of cobalt are considered. The interference with Fe(II) is eliminated by its oxidation to Fe(III). It is shown that the performance characteristics of the procedures depend on the surface concentration of the reagent. The limit of detection for cobalt is 0.01 mu g per 0.1 g of the adsorbent. The developed procedures were used for the determination of mobile cobalt species in soils.