Tungsten–rhodium permanent chemical modifier for lead determination in sediment slurries by electrothermal atomic absorption spectrometry

Abstract

A tungsten carbide–rhodium coating on the integrated platform of a transversely heated graphite atomiser was used as a permanent chemical modifier for the determination of Pb in sediment slurries by electrothermal atomic absorption spectrometry. Slurries were sonicated for 20 s before being delivered to the previously W–Rh treated platform. The number of sediment particles introduced into the atomiser for delivery of a 20 µl slurry aliquot ranged from 1300 to 3400. The permanent W–Rh modifier remains stable for approximately 250 firings when 20 µl of slurry containing up to 0.5% m/v are delivered to the atomiser. In addition, the permanent modifier increases the tube lifetime by 50–95% when compared with untreated integrated platforms. Also, there is less degradation of sensitivity during the atomiser lifetime when compared with conventional modifiers, resulting in a decreased need for re-calibration during routine analysis. Detection limits, based on integrated absorbance for 0.50% m/v slurries, were 61 ng g^–1 Pb for the 250 µg W + 200 µg Rh permanent modifier and 125 ng g^–1 Pb for 5 µg Pd + 3 µg Mg(NO₃)₂. The RSD for 735 consecutive measurements of 20 µl of a 0.50% m/v sediment slurry was 3.6% for the proposed permanent chemical modifier. Results for the determination of Pb in sediment slurries using the W–Rh permanent modifier were in agreement with those obtained with digested solutions by using Pd + Mg(NO₃)₂, since no statistical differences were found by the paired t-test at the 99% level.