Study on the Causes for ICP-MS Signal Intensity Declination of Os Water Absorption Liquid

Li-min ZHOU; Chao LI; Xin-wei LI; Hong ZHAO; Wen-jun QU; An-dao DU

doi:10.15898/j.cnki.11-2131/td.201805010054

Li-min ZHOU, Chao LI, Xin-wei LI, Hong ZHAO, Wen-jun QU, An-dao DU. Study on the Causes for ICP-MS Signal Intensity Declination of Os Water Absorption Liquid[J]. Rock and Mineral Analysis, 2018, 37(4): 431-438. DOI: 10.15898/j.cnki.11-2131/td.201805010054

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Study on the Causes for ICP-MS Signal Intensity Declination of Os Water Absorption Liquid

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BACKGROUNDOs can be separated from the sample matrix by distillation, and the absorbing liquid can be introduced into ICP-MS directly, which is a key step of the molybdenite Re-Os isotopic age analysis. However, the Os signal intensity declines significantly after long time storage. According to the properties of OsO₄, the possible causes may include:1) volatilization which reduces the Os content in the absorbing liquid, and 2) the reduction in which Os(Ⅷ) transforms to the low valence state without volatility and OsO₄ in the gas state decreases. Although they can both reduce the Os being introduced into ICP-MS ultimately, the extent of their effect is not clear.OBJECTIVESTo quantify the effects of absorbing liquid storage conditions such as duration, acidity and temperature on the Os signal intensity, to identify the cause of this decline and to find out the methods for its suppression. METHODS:The experiment consists of two parts:1) using the molybdenite Re-Os dating reference materials to construct a different absorbing liquid storage condition series, including duration, acidity and temperature, and measure their Os signal intensities in terms of ¹⁸⁷Os/¹⁹³Ir relative ratios. 2) sealing the residual absorbing liquid together with the spike and oxidizing agents within the Carius tube with sequent heating and distillation. The ¹⁸⁷Os/¹⁹⁰Os ratios were determined to calculate the Os content and the retention rate.RESULTSAfter storing, the Os signal intensities of absorbing liquids decline with time from 3.2% to 68.6%. The longer time, the lower acidity and the higher temperature for OsO₄ absorbing liquid storage, the more obvious Os signal declines. After storing at room temperature for the same time, the Os retention rate of the low-acidity series is higher than that of the high-acidity series, but the former has a lower signal intensity than the latter. This indicates that both volatilization and reduction contribute to the decline of Os signal intensity and are the main factors.CONCLUSIONSFreezing to -18℃ can inhibit the volatilization of OsO₄, whereas increasing the acidity (about 3.5 mol/L) can reduce OsO₄ reduction. The combination of the two inhibits signal attenuation, and increases the flexibility and applicability of the distillation method.

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Study on the Causes for ICP-MS Signal Intensity Declination of Os Water Absorption Liquid

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