Abstract
Blank level during the analytical process is critical for the determination of Os isotope ratios (187Os/188Os) both for high precision and accuracy. Previously, the blank level in the PGE laboratory was not good enough to measure samples with very low Os contents. To improve the blank level, we measured Os blanks in each reagent used in Os isotope analytical procedures by sparging method with ICP-QMS and tried to identify the source of Os blanks. Two major sources of Os blanks were identified; one is from nitric acid which is used in the digestion of samples, and the other is from environmental Os in the laboratory. We were able to decrease the Os blank in nitric acid to 1/3～1/2 than the original by heating and bubbling Air and N2 gas into the nitric acid. To reduce the blank contribution from environmental Os, we used closed vaporization system during the evaporation of HBr sample solution. The closed vaporization system is quite efficient to prevent the air containing environmental Os for reducing the Os blanks. As a result, the Os blank level in our laboratory was reduced significantly for the analysis of ppt-level samples.
