Field sampling system for determination of cadmium and nickel in fresh water by flame atomic absorption spectrometry

A system containing Amberlite XAD - 2 (styrene-divinylbenzene copolymers) loaded with 2(2-thiazolylazo)-5-dimethylaminophenol (TAM) reagent is proposed for field sampling, preconcentration and determination of cadmium (II) and nickel (II) ions in fresh water using flame atomic absorption spectrometry (FAAS). The optimisation process was univariate and the followings parameters were studied: pH effect, effect of sample flow rate, eluent concentration and flow rate, effect of other ions, precision and accuracy as recovery tests. In the sampling step, metal ions are retained in a minicolumn as TAM complexes. The sample is pumped at 3.0 mL min(-1) with on-line filtration using a 0.45 mu m filter. Afterwards, the minicolumn is incorporated in a flow-injection system and the metal ions eluted with a solution of 1.0 mol L-1 hydrochloric acid into the nebuliser-burner system of the spectrometer. For nickel, the limits of detection (LOD) and quantification (LOQ) were 12 and 39 ng L-1, respectively. The precision expressed as relative standard deviation (RSD) for ten independent determinations was 5.5% and 7.0% for nickel concentrations of 10 and 1.0 mu g L-1, respectively. The experimental preconcentration factor, calculated as the ratio of the slopes of the calibration curves obtained by the present procedure and manual direct aspiration was 637 for a sample volume of 150 mL. For cadmium, the LOD and LOQ are 22 ng L-1 and 72 ng L-1, respectively. The precision, expressed as RSD was 6.0% and 6.8% for cadmium concentrations of 10 and 1.0 mu g L-1, respectively. The experimental preconcentration factor was 548 also for a sample volume of 150 mL. The procedure was applied for determination of cadmium and nickel in fresh water samples with low saline concentration, collected in lagoons from Salvador City, Bahia, Brazil.