Design of a field flow preconcentration system for cadmium determination in seawater by flow-injection-atomic absorption spectrometry

A field flow preconcentration system (FFPS) for cadmium determination in seawater is described. Seawater samples are collected and preconcentrated in situ by passing them with a peristaltic pump through a minicolumn packed with Amberlite XAD-4 impregnated with the complexing agent 1-(2-pyridylazo)-2-naphthol. Thus, cadmium is complexed, retained, and preconcentrated without the interference of the saline matrix. Minicolumns loaded with cadmium are then returned to the laboratory where they are incorporated into a flow injection system and eluted with a small volume of an ethanolic solution of hydrochloric acid into the nebuliser-burner system of a flame atomic absorption spectrometer. The optimization of FFPS design is presented, and the stability and characteristics of the Cd-loaded minicolumns are studied in detail. The detection limit for Cd in seawater based on an enrichment factor of 1059 was 3.8 ng l(-1). The precision (R.S.D.) obtained for different amounts of cadmium was in the range 4.1-6.5% at the 25-100 ng l(-1) level. Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of cadmium in seawater samples from Galicia (Spain).