Solid phase extraction and spectrophotometric determination of cobalt with 2-(2-quinolinylazo)-5-dimethylaminobenzoic acid as chromogenic reagent

A sensitive, selective and rapid method has been developed for the determination mug/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 C-18 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 C-18 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 x 10(5) 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 mug/L (in original samples). This method was applied to the determination of cobalt in drinking water with good results.