A new method for the detection of ultra-trace Os and Ru in geological samples by inductively coupled plasma mass spectrometry (ICP-MS) combined with nickel sulfide fire assay and microwave-assisted digestion was proposed. Os and Ru were separated from the sample matrix in nickel sulfide fire assay stage and concentrated into FeNi sulfide button. After dissolution and filtration of FeNi sulfide button, a new microwave digestion method was carried out in this work for the complete dissolution of platinum group sulfide precipitation. The volatile behaviors of Os and Ru with concentrations ranged from 0.500 to 100.0 ng mL−1 under the proposed microwave digestion conditions were studied. Fixed volatile proportion of Os was first discovered and the average volatile proportion was 14.0% with RSD of 1.1%. The analytical performance of the proposed method was studied and the detection limits were 0.012 ng g−1 for Os and 0.014 ng g−1 for Ru. The precisions that were evaluated within five replicate results of GBW07290 were 5.2% for Os and 4.4% for Ru. Further, applied this method for the detection of Os and Ru in several reference materials including chromite, the detection results were all well agreement with the certified values, which demonstrated its' practicability for the detection of ultra-trace Os and Ru in geological samples. This method is stable and reliable. More importantly, it shows a practical method for the accurate determination of ultra-trace Os and Ru for survey large number of geological samples.
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