Development of methods for the determination of cadmium and thallium in oil shale by-products with graphite furnace atomic absorption spectrometry using direct analysis

Abstract

The purpose of this work was the development of methods for the determination of cadmium (Cd) and thallium (Tl) in oil shale by-products by graphite furnace atomic absorption spectrometry with Zeeman-effect background correction (ZBC-GF AAS) using direct analysis. Direct solid sampling (SS) was compared to slurry sampling (SlS). The pyrolysis temperatures for Cd by SS and SlS determination were 500 and 800ºC, respectively, and the atomization temperature was 1700ºC, using a mixture Pd/Mg as the chemical modifier. The limits of detection (LOD) were 3.4ngg−1 for SS and 5.5ngg−1 for SlS. For Tl determination, temperatures of pyrolysis and atomization were 900 and 1800ºC, respectively, and a chemical modifier was not employed. The LOD obtained for solid and slurry sampling analysis were 11 and 36ngg−1, respectively. The accuracy of methods was evaluated using standard reference materials BCSS1 and NIST SRM 2704. The results of the SS and SlS methods were in agreement with certified values for both elements (no significance difference with 95% of confidence level). In order to compare the results, ZBC-GF AAS and ICP-MS were employed to determine Cd and Tl after wet digestion procedures, in closed vessels assisted by microwave radiation and a conventional wet digestion in open vessels using a digester block. The results obtained by SS-GF AAS were in agreement with those obtained by ICP-MS after digestion by microwave-assisted digestion in closed vessels for all the samples investigated.