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

A tungsten carbide-rhodium coating on the integrated platform of a transver sely heated graphite atomiser was used as a permanent chemical modifier for the determination of Pb in sediment slurries by electrothermal atomic abso rption spectrometry. Slurries were sonicated for 20 s before being delivere d to the previously W-Rh treated platform. The number of sediment particles introduced into the atomiser for delivery of a 20 mu l slurry aliquot rang ed from 1300 to 3400. The permanent W-Rh modifier remains stable for approx imately 250 firings when 20 mu l of slurry containing up to 0.5% m/v are de livered 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 f or re-calibration during routine analysis. Detection limits, based on integ rated absorbance for 0.50% m/v slurries, were 61 ng g(-1) Pb for the 250 mu g W + 200 mu g Rh permanent modifier and 125 ng g(-1) Pb for 5 mu g Pd + 3 mu g Mg(NO3)(2). The RSD for 735 consecutive measurements of 20 mu l of a 0.50% m/v sediment slurry was 3.6% for the proposed permanent chemical modi fier. Results for the determination of Pb in sediment slurries using the W- Rh permanent modifier were in agreement with those obtained with digested s olutions by using Pd + Mg(NO3)(2), since no statistical differences were fo und by the paired t-test at the 99% level.