Tungsten-rhodium permanent chemical modifier for lead determination in digests of biological materials and sediments by electrothermal atomic absorption spectrometry

A tungsten carbide-rhodium coating on the integrated platform of a transversely heated graphite atomizer was used as a permanent chemical modifier for the determination of Pb in digests of biological materials and sediments by electrothermal atomic absorption spectrometry. Coating with 250 mu g W + 200 mu g Rh was as efficient as a Pd + Mg(NO3)(2) conventional modifier for obtaining good Pb recoveries (95.2-102.3%). The W-Rh permanent modifier remained stable for approximately 350 firings when 20 mu l of digested sample were delivered into the atomizer. In addition, the permanent modifier increased the tube lifetime by 50-115% with respect to untreated integrated platforms. Also, there was less degradation of sensitivity during the atomizer lifetime when compared with the conventional modifier, resulting in a decreased need for re-calibration during routine analysis. The W-Rh permanent modifier withstood acid concentrations up to 5.0% v/v HNO3 without changes in the coating lifetime as well as in the analytical signal. The detection limit, based on integrated absorbance, was 15.5 and 124 ng g(-1) Pb for biological materials and sediments, respectively. The RSDs after 1140 and 1250 consecutive measurements of 10 mu l of digested Plankton reference material and 10 mu l of River Sediment were, respectively, 3.6 and 3.3%. Results for the determination of Pb in the samples were in agreement with those obtained with digested solutions by using Pd + Mg(NO3)(2), since no statistical differences were found after applying a paired t-test at the 99% confidence level.