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

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Abstract
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 µg W+200 µg Rh was as efficient as a Pd+Mg(NO 3 ) 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 µl 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 HNO 3 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 µl of digested Plankton reference material and 10 µl 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(NO 3 ) 2 , since no statistical differences were found after applying a paired t-test at the 99% confidence level.

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