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

Abstract

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: 28-32