Capabilities and limitations of different techniques in electrothermal atomic absorption spectrometry for direct monitoring of arsenic, cadmium and lead contamination of sea-water

Abstract

Three atomization techniques for electrothermal atomic absorption spectrometry (ETAAS), namely, wall, platform and graphite probe have been tested and critically compared for the direct determination of arsenic, cadmium and lead in sea-water. The best analytical performance was obtained using totally pyrolytic graphite platforms inserted in pyrolytic graphite coated graphite tubes, peak height measurement mode and the addition of chemical modifier (10 µg of palladium as nitrate). For arsenic determination the modifier was injected together with the sample (WET mode), while for cadmium and lead determination the modifier was previously reduced to Pd⁰ by in situ thermal decomposition of the palladium nitrate (DRY mode). With regard to sample pre-treatment, the sea-water was injected directly onto the platform for arsenic measurements, while dilution with ultrapure water (1 + 1) was preferable for lead and a dilution (1 + 3) with 25% ammonium nitrate solution was needed for cadmium. The limits of detection (LODs) for the three toxic elements, relative to the real samples (undiluted sea-water) analysed, were 1.7 µg l^–1 for arsenic, 1.0 µg l^–1 for cadmium and 1.3 µg l^–1 for lead. The recoveries obtained for all three metals in sea-water samples were 100 ± 5% using the recommended ETAAS procedures. The analytical performances of the proposed methods are given. Quantification limits observed (5 × LOD) warrant the application of these methods to direct monitoring and control of contaminated waters for arsenic, cadmium and lead. However, when ‘normal’ levels of the metals in sea-water have to be determined adequate preconcentration techniques are needed.