A study on the solid phase extraction of CO(II)-IIDE chelate with C18 disk and its application to the determination of trace cobalt

Abstract

A sensitive, selective and rapid method has been developed for the determination of µg l-1 level of cobalt based on the rapid reaction of cobalt(II) with isopropyl 2-[(isopropoxy carbothioyl) disulfanyl] ethanethioate chelate (IIDE) and the solid phase extraction (SPE) of the colored chelate with Waters Porapak Sep-Park C18 disk. The isopropyl 2-[(isopropoxy carbothioyl) disulfanyl]ethanethioate chelate can react with Co(II) in the presence of pH 4.2 acetic acid /sodium acetate buffer solution and cetyl trimethylammonium bromide (CTMAB) medium to form a violet chelate of a molar ratio of 1:2 (cobalt to Isopropyl 2-[(isopropoxy carbothioyl) disulfanyl]ethanethioate chelate. This chelate can be retained on Waters Porapak Sep-Park C18 disk quantitatively when they passed the disk as aqueous solution. At the end of the enrichment, the retained chelate can be eluted from the disk by 2.5 ml of ethanol (contain 5% acetic acid). In the measured solution, the molar absorptivity of the chelate was 1.58 ×/105 1 mol -1 cm-1at 635 nm, and Beer’s law was obeyed in the range of 0.01-/0.4 µg ml-1. The relative standard deviation for 11 replicate sample of 0.01 µg.ml-1 level was 2.54%. The detection limit was 0.01 µg ml-1 (in original samples). This method can be applied for the determination of µg ml-1 level of cobalt in drinking water with satisfactory results. Key words: Cobalt, solid phase extraction spectrophotometry, isopropyl 2-[(isopropoxy carbothioyl) disulfanyl] ethanethioate chelate (IIDE).