Evaluation of tungsten-rhodium coating on an integrated platform as a permanent chemical modifier for cadmium, lead, and selenium determination by electrothermal atomic absorption spectrometry

A tungsten-rhodium coating on the integrated platform of a transversely heated graphite atomizer is proposed as a permanent chemical modifier for the determination of Cd, Pb, and Se by electrothermal atomic absorption spectrometry. It was demonstrated that coating with 250 mu g W + 200 mu g Rh is as efficient as the conventional Mg(NO3)(2) + NH4H2PO4 or Pd + Mg(NO3)(2) modifiers for avoiding most serious interferences. The permanent W-Rh modifier remains stable for 300-350 firings of the furnace, and increases tube lifetime by 50%-100% when compared to pyrolytic carbon integrated platforms. Also, there is less degradation of sensitivity during the atomizer lifetime when compared with the conventional modifiers, resulting in a decreased need of re-calibration during routine analysis. The characteristic masses and detection limits achieved using the permanent modifier were respectively: Cd 1.1 +/- 0.4 pg and 0.020 mu g L-1; Pb 30 +/- 3 pg and 0.58 mu g L-1 and Se 42 +/- 5 pg and 0.64 mu g L-1. Results from the determination of these elements in water reference materials were in agreement with the certified values, since no statistical differences were found by the paired t-test at the 95% level. (C) 1998 Elsevier Science B.V. All rights reserved.