Solid-phase extraction and determination of ultra trace amounts of lead, mercury and cadmium in water samples using octadecyl silica membrane disks modified with 5,5′-dithiobis(2-nitrobenzoic acid) and atomic absorption spectrometry

A simple and fast method for preconcentration and determination of ultra trace amounts of lead(II), mercury(II) and cadmium(II) in water samples is presented. Lead, mercury and cadmium adsorbed quantitatively during passage of water samples (pH = 7, flow rate = 20 mL min(-1)) through octadecyl silica membrane disks modified with 5,5'-dithiobis(2-nitrobenzoic acid). The retained lead, mercury and cadmium are then stripped from the disk with a minimal amount of I M hydrochloric acid solution as eluent, and determined by atomic absorption spectrometry. The influence of flow rates of the eluent and sample solution, the amount of ligand, type and least amount of eluent, pH of sample, effect of other ions and breakthrough volume are determined. The breakthrough volume of the method is greater than 2000 mL for lead and greater than 1500 mL for mercury and cadmium, which results in an enrichment factor of 200 for lead and an enrichment factor of 150 for both mercury and cadmium. The limit of detection of the proposed method is 177, 2 and 13 ngl(-1) for lead, mercury and cadmium, respectively.