Abstract
A sensitive, selective and rapid method for the determination of cobalt based on the rapid reaction of cobalt(II) with 2-(2-quinolinylazo)-5-dimethylaminoaniline (QADMAA) and the solid phase extraction of the Co(II)-QADMAA chelate with C18 membrane disks was developed. In the presence of pH 5.5 buffer solution and cetyl trimethylammonium bromide (CTMAB) medium, QADMAA reacts with cobalt to form a violet complex of a molar ratio 1:2 (cobalt to QADMAA). This chelate was enriched by the solid phase extraction with C18 membrane disks. The enrichment factor of 50 was obtained by elution of the chelate form the disks with minimal amount of isopentyl alcohol. In isopentyl alcohol medium, the molar absorptivity of the chelate is 1.32¡Á105 L.mol-1.cm-1 at 616 nm. Beer's law is obeyed in the range of 0.01- 0.6 mg/mL in the measured solution. The relative standard deviation for eleven replicate sample of 0.01 mg/mL level is 1.35 %. The detection limit reaches 0.02 mg/L in the original samples. This method was applied to the determination of cobalt in environmental samples with good results.
Keywords 2-(2-quinolinylazo)-5-dimethylaminoaniline; cobalt, solid phase extraction spectrophotometry
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