Frick Daniel A, Schuessler Jan A, von Blanckenburg Friedhelm
GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany.
GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany.
Anal Chim Acta. 2016 Sep 28;938:33-43. doi: 10.1016/j.aca.2016.08.029. Epub 2016 Aug 21.
Stable metal (e.g. Li, Mg, Ca, Fe, Cu, Zn, and Mo) and metalloid (B, Si, Ge) isotope ratio systems have emerged as geochemical tracers to fingerprint distinct physicochemical reactions. These systems are relevant to many Earth Science questions. The benefit of in situ microscale analysis using laser ablation (LA) over bulk sample analysis is to use the spatial context of different phases in the solid sample to disclose the processes that govern their chemical and isotopic compositions. However, there is a lack of in situ analytical routines to obtain a samples' stable isotope ratio together with its chemical composition. Here, we evaluate two novel analytical routines for the simultaneous determination of the chemical and Si stable isotope composition (δ(30)Si) on the micrometre scale in geological samples. In both routines, multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) is combined with femtosecond-LA, where stable isotope ratios are corrected for mass bias using standard-sample-bracketing with matrix-independent calibration. The first method is based on laser ablation split stream (LASS), where the laser aerosol is split and introduced simultaneously into both the MC-ICP-MS and a quadrupole ICP-MS. The second method is based on optical emission spectroscopy using direct observation of the MC-ICP-MS plasma (LA-MC-ICP-MS|OES). Both methods are evaluated using international geological reference materials. Accurate and precise Si isotope ratios were obtained with an uncertainty typically better than 0.23‰, 2SD, δ(30)Si. With both methods major element concentrations (e.g., Na, Al, Si, Mg, Ca) can be simultaneously determined. However, LASS-ICP-MS is superior over LA-MC-ICP-MS|OES, which is limited by its lower sensitivity. Moreover, LASS-ICP-MS offers trace element analysis down to the μg g(-1)-range for more than 28 elements due to lower limits of detection, and with typical uncertainties better than 15%. For in situ simultaneous stable isotope measurement and chemical composition analysis LASS-ICP-MS in combination with MC-ICP-MS is the method of choice.
稳定金属（如锂、镁、钙、铁、铜、锌和钼）和类金属（硼、硅、锗）同位素比值体系已成为地球化学示踪剂，用于区分不同的物理化学反应。这些体系与许多地球科学问题相关。使用激光烧蚀（LA）进行原位微尺度分析相对于批量样品分析的优势在于，利用固体样品中不同相的空间背景来揭示控制其化学和同位素组成的过程。然而，目前缺乏能够同时获取样品稳定同位素比值及其化学成分的原位分析方法。在此，我们评估了两种用于同时测定地质样品中微米尺度化学组成和硅稳定同位素组成（δ(30)Si）的新型分析方法。在这两种方法中，多接收电感耦合等离子体质谱仪（MC-ICP-MS）与飞秒激光烧蚀相结合，通过与基体无关校准的标准样品夹法校正稳定同位素比值的质量偏差。第一种方法基于激光烧蚀分流（LASS），即将激光气溶胶分流并同时引入MC-ICP-MS和四极杆ICP-MS。第二种方法基于对MC-ICP-MS等离子体的直接观测进行光发射光谱分析（LA-MC-ICP-MS|OES）。使用国际地质参考物质对这两种方法进行了评估。获得了准确且精确的硅同位素比值，其不确定度通常优于0.23‰，2SD，δ(30)Si。使用这两种方法均可同时测定主要元素浓度（如钠、铝、硅、镁、钙）。然而，LASS-ICP-MS优于LA-MC-ICP-MS|OES，后者受较低灵敏度的限制。此外，由于检测限较低，LASS-ICP-MS能够对超过28种元素进行低至μg g(-1)范围的微量元素分析，其典型不确定度优于15%。对于原位同时稳定同位素测量和化学成分分析，LASS-ICP-MS与MC-ICP-MS相结合是首选方法。
