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 µg of cobalt in 5 ml of final DMF solution. Seven replicate determinations of 12 µg 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 µg 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.