高精度热电离质谱（TIMS）在南极陨石研究中的应用前景

热电离质谱（TIMS）是同位素地球化学研究中传统、可靠、分析精度高的主要测试仪器之一，尤其对于微量样品的高精度同位素比值测定，以其高精度和高灵敏度获得广泛的认可，这一特征在天体化学微量样品同位素研究中具有广阔的应用前景。目前，新型TRITON TIMS质谱仪已实现了Re–Os，Cr，Sr，Nd，Pb等同位素的高精度测定。采用TIMS测定Sr同位素比值的Sr含量范围可由10pg—100ng以上，87Sr/88Sr比值测定精度可达到5‰—5ppm；LaJolla Nd同位素标样测试结果为：143Nd/144Nd=0.511842±0.000005（2SE，n=28），143Nd/144Nd比值测定精度最佳可达2ppm；207Pb–204Pb双稀释剂法对Pb含量为5—20ng样品测定，外部精度206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别达到±0.0034、±0.0046和±0.0100（2SE，n=28）；负离子状态（NTIMS）下对Os含量低至几—几十pg的样品测定187Os/188Os比值精度可达0.2‰以内，对Os含量为ng级的样品，187Os/188Os比值精度好于20ppm；Cr同位素比值50Cr/52Cr，53Cr/52Cr，54Cr/52Cr的分析精度分别可达到1ppm，2ppm，2ppm（2SD）以内。这些方法涵盖了亲石元素、亲铁元素，长寿命放射性同位素和短寿命灭绝核素的同位素研究，为我国南极陨石的深入研究提供了有力技术保障。

THE PROSPECT OF HIGH-PRECISION THERMAL IONIZATION MASS SPECTROMETRY(TIMS) APPLICATIONS IN ANTARCTIC METEORITES

The thermal ionization mass spectrometry (TIMS) is one of the most important techniques for isotopic measurements. TIMS technology has a broad prospect of application in cosmochemistry because of the high accuracy and sensitivityse. TRITON TIMS can mesure high–precision isotopic compositions of Re–Os、Cr、Sr、Nd and Pb systematics of meteorites. Small loads (10pg–100 ng Sr) of international standard NBS 987 were analyzed for 87Sr/86Sr isotope ratios with an precision of 5‰ to 5ppm by TIMS. The ratios of 143Nd/144Nd of LaJolla-Nd is 0.511842±0.000005 (2SE, n=28) in our lab, and the best precision is better than 2ppm. Using 207Pb–204Pb double spike, the reproducibilities of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb can be better than ±0.0034, ±0.0046 and ±0.0100 (n=28, 2SD) for content of 5–20ng Pb samples respectively. 187Os/188Os isotopic ratios are determined under negative thermal ions mode with the precision of better than 0.2‰ for approximately tens of pg, and 20ppm for ~ng. In addition, Cr isotopes can also be measured by TIMS technique in the static multicollection mode, the precision of 50Cr/52Cr, 53Cr/52Cr, 54Cr/52Cr ratios attain to 1ppm, 2ppm and 2ppm respectively. These methods include different isotope systematics relate to lithophile and siderophile elements, long-lived radionuclides and the short-lived extinct radionuclides. And they will provide support for further study on Antarctic meteorites.