Derivative Spectrophotometric Determination of Cobalt in Alloys and Biological Samples after Preconcentration with the Ion Pair of Disodium 1-Nitroso-2-naphthol-3,6-disulfonate and Tetradecyldimethylbenzylammonium Chloride on Microcrystalline Naphthalene or Column Method

Abstract

Cobalt was quantitatively retained by disodium 1-nitroso-2-naphthol-3,6-disulfonate (nitroso-R salt) and tetradecyldimethylbenzylammonium chloride (TDBA+Cl-) on microcrystalline naphthalene in the pH range 3.6 - 8.2 from large volumes of aqueous solutions of various alloys and biological samples. After filtration, a solid mass consisting of the cobalt complex and naphthalene was dissolved with 5 ml of dimethylformamide (DMF), and the metal was determined by third-derivative spectrophotometry. The cobalt complex could alternatively be quantitatively adsorbed on tetradecyldimethylbenzylammonium-naphthalene adsorbent packed in a column and determined similarly. The detection limit was 30 ppb (signal to noise ratio = 2) and the calibration curve was linear for 0.1 - 11 ppm in dimethylformamide solution with a correlation coefficient of 0.9996 by measuring the distance, d3A/d λ3, between λ1 (612 nm) and λ2 (579 nm). Eight replicated determinations of 2 ppm of cobalt in dimethylformamide solution gave a mean intensity (peak to peak signal between λ1 and λ2) of 0.436 with a relative standard deviation of ±0.91%. The sensitivity of the method was 0.215 (d3A/dnm3) ml/µg, which was found from the slope of the calibration curve. Various parameters, such as the effect of the pH, the volume of the aqueous phase and the interference of a number of metal ions on the determination of cobalt has been studied in detail to optimize the conditions for the determination cobalt in various alloys and biological samples.