Application of tungsten-rhodium permanent chemical modifier in slurry analysis: Determination of cadmium

A tungsten-rhodium coating on the integrated platform of a transversely hea ted graphite atomiser (THGA) was used as a permanent chemical modifier for the determination of Cd in sediment slurries by electrothermal atomic absor ption spectrometry. Slurries were ultrasonicated during 20 s before being d elivered to the previously W-Rh treated platform. The permanent W-Rh modifi er remains stable by approximately 250 measurements when 20 mu l of slurrie s containing up to 1.0% m/v are delivered into the atomiser. In addition, t he permanent modifier increases the tube lifetime up to 720 analytical firi ngs. Also, when the W-Rh permanent modifier was employed, there was less va riation of the slope of the analytical curves during the total atomiser lif etime, resulting in a decreased need of re-calibration during routine analy sis, increasing the sample throughput. The atomiser lifetime was limited to the THGA wall durability, because the W-Rh treated platform was intact after more than 720 analytical firings. Detection limits based on integrated absorbance for 1.0% m/v slurries were 1.5 ng g(-1) Cd for 250 mu g W +200 mu g Rh permanent modifier and 11.5 ng( -1) Cd for 5 mu g Pd +3 mu g Mg(NO3)(2). Results for the determination of cadmium in sediment slurries using the W-R h permanent modifier were in agreement with those obtained with dissolved s ample solutions by using Pd + Mg(NO3)(2), since no statistical differences were found by the paired t-test at the 99% level.