Column preconcentration of cobalt with the ion pair of 2-nitroso-1-naphthol-4-sulfonic acid–tetradecyldimethylbenzylammonium chloride supported on naphthalene using second-derivative spectrophotometry

Abstract

Cobalt is quantitatively retained on 2-nitroso-1-naphthol-4-sulfonic acid–tetradecyldimethylbenzylammonium (TDBA⁺)–naphthalene adsorbent in a chromatographic column in the pH range 6.1–9.0 at a flow rate of 1 ml min^–1 from a large volume of aqueous solutions of various alloys. The solid mass consisting of the cobalt complex and naphthalene was dissolved out of the column with 5 ml of dimethylformamide (DMF) and the metal was determined by second-derivative spectrophotometry in the concentration range 1.0–60.0 µg per 5 ml of the final DMF solution. Seven replicate determinations of 20 µg of cobalt gave a mean peak height of 0.128 with a relative standard deviation of 1.4%. The sensitivity of the method is 0.019 µg ml^–1, found from the slope of the calibration graph. The interference of a large number of anions and cations was studied and the optimized conditions have been utilized for the trace determination of cobalt in standard reference materials. The method may also be applied to the trace determination of cobalt in various biological and environmental samples.