Selective Extraction/ Preconcentration of Cadmium (II) in Environmental Samples by an Anion Exchanger on Octadecyl Silica Membrane Disk

A simple and selective solid phase extraction of trace amounts of cadmium is developed for determination by flame atomic absorption spectrometry. Cadmium ions were quantitatively retained as ion pair by passing the aqueous solution of cadmium containing iodide ions and ceyltrimethylammonium bromide, through an octadecyl-bonded silica membrane disk, while almost all matrix elements were passed through. The retained cadmium ions were then washed off from the disk by minimal amount of HNO3 in ethanol and determined by flame atomic absorption spectrometry. The maximum capacity of the disk in presence of 3 ×10-4mol l-1surfactant was found to be 590 ± 5 μg of cadmium. The method permitted enrichment factor of 200. A good precision for 10 μg l-1cadmium (1.0 % R.S.D, n = 6), and detection limit (3Sb m-1) 0.05 μg l-1 were obtained. The accuracy was assessed by analysis of spiked samples and independent analysis by ICP-AES.