COLUMN PRECONCENTRATION OF COBALT IN ALLOYS AND PEPPERBUSH USING 2-(5-BROMO-2-PYRIDYLAZO)-5-DIETHYLAMINOPHENOL AND AMMONIUM TETRAPHENYLBORATE ADSORBENT SUPPORTED ON NAPHTHALENE WITH SUBSEQUENT DETERMINATION USING ATOMIC-ABSORPTION SPECTROMETRY

A method has been established for column preconcentration and determination of cobalt using an ion-pair produced from an ammonium cation and a tetraphenylborate (TPB) anion supported on naphthalene in a simple funnel-tipped glass tube. Cobalt forms a water-soluble chelate cation with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). The chelate cation is retained as a water-insoluble Co-5-Br-PADAP-TPB complex on the surface of the naphthalene, which is packed in a column. Cobalt is quantitatively retained on the ammonium tetraphenylborate adsorbent supported on the naphthalene in the pH range 3.0-8.0 at a flow rate of 1 ml min-1. The solid mass is stripped from the column with 5 ml of dimethylformamide (DMF) and the cobalt determined by flame atomic absorption spectrometry at 240.7 nm. The calibration graph is linear over the concentration range from 1 to 20 mug of cobalt in 5 ml of final DMF solution. Seven replicate determinations of 12 mug of cobalt gave a mean absorbance of 0.124 with a relative standard deviation of 1.0%. The sensitivity for a 1% absorption is 0.085 mug ml-1. The effect of foreign ions was studied and the proposed method applied to the determination of cobalt in certified reference material samples of alloy, steel and pepperbush.