Accurate isotope ratio measurements are of high importance in various scientific fields, ranging from radio isotope geochronology of solids to studies of element isotopes fractionated by living organisms. Instrument limitations, such as unresolved isobaric inferences in the mass spectra, or cosampling of the material of interest together with the matrix material may reduce the quality of isotope measurements. Here, we describe a method for accurate isotope ratio measurements using our laser ablation ionization time‐of‐flight mass spectrometer (LIMS) that is designed for in situ planetary research. The method is based on chemical depth profiling that allows for identifying micrometer scale inclusions embedded in surrounding rocks with different composition inside the bulk of the sample. The data used for precise isotope measurements are improved using a spectrum cleaning procedure that ensures removal of low quality spectra. Furthermore, correlation of isotopes of an element is used to identify and reject the data points that, for example, do not belong to the species of interest. The measurements were conducted using IR femtosecond laser irradiation focused on the sample surface to a spot size of ~12 μm. Material removal was conducted for a predefined number of laser shots, and time‐of‐flight mass spectra were recorded for each of the ablated layers. Measurements were conducted on NIST SRM 986 Ni isotope standard, trevorite mineral, and micrometer‐sized inclusions embedded in aragonite. Our measurements demonstrate that element isotope ratios can be measured with accuracies and precision at the permille level, exemplified by the analysis of B, Mg, and Ni element isotopes. The method applied will be used for in situ investigation of samples on planetary surfaces, for accurate quantification of element fractionation induced by, for example, past or present life or by geochemical processes.

中文翻译：

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飞秒激光烧蚀电离质谱法测量同位素丰度比

从固体的放射性同位素年代学到研究由活生物体分离出的元素同位素，准确的同位素比测量在各个科学领域都具有重要意义。仪器的局限性，例如质谱图中尚未解决的等压推断，或感兴趣的材料与基质材料一起共同采样可能会降低同位素测量的质量。在这里，我们描述了一种使用我们的激光烧蚀电离飞行时间质谱仪（LIMS）进行精确同位素比测量的方法，该方法专为原位行星研究而设计。该方法基于化学深度剖析，该化学深度剖析可以识别嵌入在样品内部不同组成的围岩中的微米级夹杂物。用于精确同位素测量的数据通过使用光谱清洗程序得以改善，该程序可确保去除低质量的光谱。此外，元素同位素的相关性用于识别和拒绝例如不属于目标物种的数据点。使用聚焦在样品表面至约12μm斑点大小的IR飞秒激光辐照进行测量。对材料进行预定义数量的激光去除，并记录每个烧蚀层的飞行时间质谱图。使用NIST SRM 986 Ni同位素标准品，水润矿物和嵌入文石的微米级夹杂物进行测量。我们的测量结果表明，可以在准直度水平上精确测量元素同位素比，通过分析B，Mg和Ni元素同位素来举例说明。所应用的方法将用于行星表面样品的原位研究，以准确定量由例如过去或现在的生命或地球化学过程引起的元素分级分离。