The Synthesis of QADMAA and its Application to the Solid Phase Extraction and Spectrophotometric Determination of Cobalt

In this paper, the synthesis of a new chromogenic reagent, 2-(2-quinolylazo)-5-dimethylaminoaniline (QADMAA), is reported. A sensitive, selective and rapid method for the determination of cobalt based on the rapid reaction of cobalt(II) with QADMAA and the solid phase extraction of the Co(II)-QADMAAchelate withC18 membrane disks was developed. In the presence of a pH=5.5 buffer solution and a cetyl trimethylammonium bromide (CTMAB) medium, QADMAA reacts with cobalt to form a violet complex with a molar ratio of 1:2 (cobalt to QADMAA). This chelate was enriched by solid phase extraction with C18 membrane disks and an enrichment factor of 50 was obtained. The molar absorptivity of the chelate is 1.32x105 L mol-1 cm-1 at 616 nm in the measured solution. Beer's law is obeyed in the range of 0.01~0.6 mg mL-1. The relative standard deviation for eleven replicate sample at the 0.01 mg mL-1 level is 1.35%. The detection limit reached 0.02 mg L-1 in the original samples. This method was applied with good results to the determination of cobalt in environmental samples. Keywords: 2-(2-Quinolylazo)-5-dimethylaminoaniline Cobalt Spectrophotometry Solid phase extraction South African Journal of Chemistry Vol.57 2004: 28-3