SOLID PHASE EXTRACTION AND SPECTROPHOTOMETRIC DETERMINATION OF COBALT WITH 2-(2-QUINOLINYLAZO)-5-DIMETHYLAMINOBENZOIC ACID AS CHROMOGENIC REAGENT

Abstract

A sensitive, selective and rapid method has been developed for the determination µg/L (ppb) level of cobalt(II) based on the rapid reaction of cobalt(II) with 2-(2-quinolinylazo)-5-dimethylaminobenzoic acid (QADMAB) and the solid phase extraction of the colored chelate with C18 cartridge. The QADMAB reacts with Co(II) in the acetate buffer (pH 4.0) and cetyl trimethylammonium bromide (CTMAB) medium, forming a violet chelate of a molar ratio 1 : 2 (cobalt to QADMAB). This chelate can be extracted by C18 cartridge and eluted by ethanol (containing 5% acetic acid). Enrichment factor of 100 was achieved. In this medium, the molar absorptivity of the chelate was 1.40 × 105 L mol−1 cm−1 at 625 nm. Beer's law is obeyed in the range of 0.01–0.4 mg/L. The relative standard deviation for eleven replicate samples of 0.01 mg/L is 2.36%. The detection limit is 0.03 µg/L (in original samples). This method was applied to the determination of cobalt in drinking water with good results.