State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China.
Anal Chem. 2012 Dec 18;84(24):10686-93. doi: 10.1021/ac302327g. Epub 2012 Dec 5.
Complete sample digestion is a prerequisite for achieving reproducible and accurate analytical results for geological samples. Open-vessel acid digestions successfully dissolve mafic samples, but this method cannot achieve complete dissolution of felsic samples, because of the presence of refractory minerals such as zircon. In this study, an efficient and simplified digestion technique using the solid compound NH(4)HF(2) in a screw-top vial has been developed for multielement analysis of different types of rock samples. NH(4)HF(2) has a higher boiling point (239.5 °C) than conventional acids such as HF, HNO(3) and HCl, which allows for an elevated digestion temperature in open vessels, enabling the decomposition of refractory phases. Similar to HF, HNO(3) and HCl, ultrapure NH(4)HF(2) can be produced using a conventional PFA sub-boiling (heating and cooling) purification system. A digestion time of 2-3 h for 200 mg NH(4)HF(2) in a Savillex Teflon vial at 230 °C is sufficient to digest 50 mg of the felsic rock GSP-2, which is ~6 times faster than using conventional closed-vessel acid digestion at 190 °C (high-pressure PTFE digestion bomb). The price of a Savillex Teflon vial is far less than the price of a high-pressure PTFE digestion bomb (consisting of a PTFE inner vessel and an outer stainless steel pressure jacket). Moreover, the NH(4)HF(2)-open-vessel acid digestion is not hampered by the formation of insoluble fluorides. We have successfully applied the NH(4)HF(2)-open-vessel acid digestion to the digestion of a series of international geological reference materials, including mafic to felsic igneous rocks and shales. This method provides an effective, simple, economical, and comparatively safe dissolution method that combines the advantages of both the open- and closed-vessel digestion methods.
完全的样品消解是获得地质样品重现性和准确性分析结果的前提。开放式酸消解成功地溶解了镁铁质样品，但由于存在锆石等难熔矿物，这种方法不能完全溶解长英质样品。在本研究中，开发了一种使用螺口管中的固体化合物 NH(4)HF(2)的高效、简化的消解技术，用于不同类型岩石样品的多元素分析。NH(4)HF(2)的沸点（239.5°C）高于 HF、HNO(3)和 HCl 等常规酸，这允许在开放式容器中升高消解温度，使难熔相分解。与 HF、HNO(3)和 HCl 相似，超纯 NH(4)HF(2)可以使用常规的 PFA 亚沸（加热和冷却）纯化系统来生产。在 230°C 下，200mg NH(4)HF(2)在 Savillex Teflon 管中消解 2-3 小时，足以消解 50mg 长英质岩石 GSP-2，这比在 190°C（高压 PTFE 消解弹）下使用常规的密闭酸消解快约 6 倍。Savillex Teflon 管的价格远低于高压 PTFE 消解弹（由 PTFE 内容器和外部不锈钢压力套组成）的价格。此外，NH(4)HF(2)-开放式酸消解不受不溶性氟化物形成的阻碍。我们已经成功地将 NH(4)HF(2)-开放式酸消解应用于一系列国际地质标准物质的消解，包括镁铁质到长英质火成岩和页岩。这种方法提供了一种有效、简单、经济且相对安全的溶解方法，结合了开放式和密闭式消解方法的优点。
