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

A tungsten carbide-rhodium coating on the integrated platform of a transver sely heated graphite atomizer was used as a permanent chemical modifier for the determination of Cd in fish slurries by electrothermal atomic absorpti on spectrometry. Slurries were sonicated for 25 s before being delivered to the previously W-Rh treated platform. The number of fish particles introdu ced into the atomizer for delivery of a 20 mu l slurry aliquot ranged from 7900 to 47 000. It was demonstrated that coating with 250 mu g of W + 200 m u g of Rh is as efficient as a Pd + Mg(NO3)(2) conventional modifier for ob taining good Cd recoveries (93.4-103.5%). The permanent W-Rh modifier remai ns stable for approximately 300 firings when 20 mu l 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 int egrated platforms. Also, there is less degradation of sensitivity during th e atomizer lifetime when compared with the conventional modifiers, resultin g in a decreased need for re-calibration during routine analysis. The detec tion 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 mu l 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 permane nt modifier were in agreement with those obtained with digested solutions b y using Pd + Mg(NO3)(2), since no statistical differences were found by a p aired t-test at the 99% level.