Evaluation of Rh, Ir, Ru, W-Rh, W-Ir and W-Ru as permanent modifiers for the determination of lead in ashes, coals, sediments, sludges, soils, and freshwaters by electrothermal atomic absorption spectrometry

Different permanent modifiers (Rh, Ir, Ru, W-Rh, W-Ru and W-Ir) thermally deposited on the integrated platform of transversally heated graphite atomizer (TGA) were employed for the determination of lead in ashes, coals, sediments, sludges, soils and freshwaters by electrothermal atomic absorption spectrometry (ETAAS). Microwave digests of solid samples and water samples were employed for obtaining the analytical characteristics of the methods with different permanent modifiers. The performance of the modifiers for lead determination in the real samples depended strongly on the type of permanent modifier chosen. The Rh, Ir and Ru permanent modifiers were suitable for the analyte determinations in simpler matrices such as waters (recoveries of certified values 95-103%), but the analyte recoveries of certified values in sludges, soils, sediments, coals and ashes were lower than 90%. On the other hand, for the determination of lead, using W-Rh, W-Ru and W-Ir pemanent modifiers presented recoveries of certified values within 95-105% for all the samples. Long-term stability curves obtained for the determination of lead in environmental samples with different permanent modifiers (Rh, Ir, Ru, W-Rh, W-Ir and W-Ru) showed that the improvement in analytical firings of the tube depends on the tungsten deposit onto the platform. The graphite tube coated with tungsten-noble metal permanent modifier presents a number of analytical firings about 20% longer when compared with single permanent modifier. The results for the determination of Pb employing different permanent modifiers in the samples were in agreement with the certified reference materials, since no statistical differences were found after applying the paired t-test at the 95% confidence level