Tetradecyldimethylbenzylammonium thiocyanate adsorbent supported on naphthalene for the preconcentration and determination of cobalt in aluminium alloys and steels using atomic absorption spectrometry

Abstract

A solid ion-pair material produced from tetradecyldimethylbenzylammonium chloride (TDBA) and ammonium thiocyanate on naphthalene provides a simple, rapid and selective technique of preconcentrating cobalt from up to 200 ml of aqueous solution. Cobalt reacts with sodium 1-nitroso-2-naphthol-3,6-disulphonate (nitroso-R salt) to form a brown, water-soluble chelate anion. The chelate anion forms a water-insoluble Co-nitroso-R salt-TDBA complex on naphthalene packed in a column and trace cobalt is quantitatively retained on the naphthalene in the pH range 2.7–11.0 at a flow-rate of 2 ml min −1. The solid mass is stripped from the column with 5 ml of dimethylformamide (DMF) and cobalt is measured by atomic absorption spectrometry (AAS) at 241 nm. The calibration graph is linear over the concentration range 0.5–15μg Co in 5 ml of dimethylformamide solution. Seven replicate determinations of 9 μg of cobalt gave a mean absorbance of 0.095 with a relative standard deviation of 1.7%. The sensitivity for 1% absorption was 0.0834μg ml −1 (0.240 μg ml −1 for direct AAS on the aqueous solution). The proposed method was utilized for the determination of cobalt in standard aluminium alloys and steel samples.