The use of tungsten–rhodium permanent chemical modifier for cadmium determination in decomposed samples of biological materials and sediments by electrothermal atomic absorption spectrometry Original Research Article

A 250 μg W + 200 μg Rh coating (W–Rh) on the integrated platform of a transversely heated graphite atomiser (THGA) was used as a permanent chemical modifier for the determination of Cd in digests of biological materials and dissolved sediments by electrothermal atomic absorption spectrometry (ETAAS). The W–Rh permanent modifier was as efficient as NH4H2PO4 + Mg(NO3)2 and Pd + Mg(NO3)2 conventional modifiers for obtaining good Cd thermal stabilisation in the decomposed samples. The permanent W–Rh modifier remained stable by approximately 300–350 firings when 20 μl of digested sample were delivered into the atomiser. In addition, the permanent modifier increased the tube lifetime up to 1450 analytical measurements in the decomposed samples containing 1.0% v/v HNO3. Also, when the W–Rh permanent modifier was employed, there was less variation of the slope of the analytical curves during the total atomiser lifetime, resulting in a decreased need of recalibration during routine analysis, increasing the sample throughput, and consequently diminishing the variable analytical costs. The atomiser lifetime was limited to the THGA wall durability, because the W–Rh treated platform was intact after more than 1200 analytical firings. The W–Rh permanent modifier withstood acidic concentrations up to 5.0% v/v HNO3 without changes in the coating lifetime as well as in the analytical signal. Detection limits obtained with W–Rh permanent modifier were 1.0 and 6 ng g−1 Cd for biological materials and sediments, which were 1.25 and 2.5 times better than NH4H2PO4 + Mg(NO3)2 and Pd + Mg(NO3)2 mixtures, respectively. Results for the determination of cadmium in the samples were in agreement with those obtained with decomposed sample solutions by using NH4H2PO4 + Mg(NO3)2 and Pd + Mg(NO3), since no statistical differences were found after applying the paired t-test at the 99% level.