Tungsten-rhodium permanent chemical modifier for cadmium determination in fish slurries by electrothermal atomic absorption spectrometry

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 Cd in fish slurries by electrothermal atomic absorption spectrometry. Slurries were sonicated for 25 s before being delivered to the previously W-Rh treated platform. The number of fish particles introduced into the atomizer for delivery of a 20 µl slurry aliquot ranged from 7900 to 47 000. It was demonstrated that coating with 250 µg of W+200 µg of Rh is as efficient as a Pd+Mg(NO ₃ ) ₂ conventional modifier for obtaining good Cd recoveries (93.4-103.5%). The permanent W-Rh modifier remains stable for approximately 300 firings when 20 µl of slurries containing up to 1.5% m/v are delivered into the atomizer. In addition, the permanent modifier increases the tube lifetime by 50-90% compared with untreated integrated platforms. Also, there is less degradation of sensitivity during the atomizer lifetime when compared with the conventional modifiers, resulting in a decreased need for re-calibration during routine analysis. The detection limit based on integrated absorbance was 1.4 ng g ^–1 Cd for 1.50% m/v slurries. The RSD for 650 consecutive measurements of 20 µl of 0.50% m/v fish slurry was 5.0% for the proposed permanent chemical modifier. Results for the determination of cadmium in fish slurries using the W+Rh permanent modifier were in agreement with those obtained with digested solutions by using Pd+Mg(NO ₃ ) ₂ , since no statistical differences were found by a paired t-test at the 99% level.