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ATOMIC ABSORPTION SPECTROMETRIC DETERMINATION OF TRACE AMOUNTS OF COBALT AFTER SEPARATION AND PRECONCENTRATION WITH USE OF 5-Br-PADAP

ABSTRACT Cobalt is quantitatively retained on 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP)-ammonium tetraphenylborate with microcrystalline naphthalene or by a column method in the pH range 3.5–9.5 from large volumes of aqueous solutions of various samples. After filtration, each solid mass consisting of the cobalt complex and naphthalene was dissolved with 5 mL of dimethylformamide and the metal was determined by flame atomic absorption spectrometry. Cobalt complex can alternatively be quantitatively adsorbed on ammonium tetraphenylborate–naphthalene adsorbent packed in a column and determined similarly. In this case, 0.15 µg of cobalt can be concentrated in a column from 600 mL of aqueous sample, where its concentration is as low as 0.25 ppb. Eight replicate determinations of 0.7 ppm of cobalt gave a mean absorbance of 0.085 with a relative standard deviation of 1.6%. The sensitivity for 1% absorption was 36 ppb. The interference of a large number of anions and cations has been studied and the optimized conditions developed were utilized for the trace determination of cobalt in various standard samples.