Study on the solid phase extraction of Co(II)-QADEAB chelate with C18 disk and its application to the determination of trace cobalt

A sensitive, selective and rapid method has been developed for the determination mug l(-1) level of cobalt based on the rapid reaction of cobalt(II) with 2-(2-quinolylazo)-5-diethylaminobenzoic acid (QADEAB) and the solid phase extraction (SPE) of the colored chelate with Waters Porapak(R) Sep-Park C-18 disk. The QADEAB can react with Co(II) in the presence of pH 3.8 acetic acid-sodium acetate buffer solution and cetyl trimethylammonium bromide (CTMAB) medium to form a violet chelate of a molar ratio 1:2 (cobalt to QADEAB). This chelate can retained on Waters Porapak(R) Sep-Park C-18 disk quantitatively when they passed the disk as aqueous solution. After the enrichment finished, the retained chelate can be eluted from disk by 2.5 ml of ethanol (contain 5% acetic acid). In the measured solution, the molar absorptivity of the chelate is 1.58 x 10(5) l mol(-1) cm(-1) at 635 nm, and Beer's law is obeyed in the range of 0.01-0.4 mug ml(-1). The relative standard deviation for I I replicate sample of 0.01 mug ml(-1) level is 2.23%. The detection limit is 0.01 mug l(-1) (in original samples). This method can be applied to the determination of mug l(-1) level of cobalt in drinking water with satisfactory results. (C) 2002 Elsevier Science B.V. All rights reserved.