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首页> 外文期刊>Journal of mass spectrometry: JMS >Isotope abundance ratio measurements using femtosecond laser ablation ionization mass spectrometry
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Isotope abundance ratio measurements using femtosecond laser ablation ionization mass spectrometry

机译：使用飞秒激光烧蚀电离质谱法测量同位素丰度比率

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摘要

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 mu m. 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.
机译：从固体放射性同位素地质年代学到生物分馏元素同位素的研究，精确的同位素比值测量在各个科学领域都具有重要意义。仪器的局限性，如质谱中未解决的等压推断，或相关材料与基质材料的共采样，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激光烧蚀电离飞行时间质谱仪（LIMS）精确测量同位素比值的方法，该质谱仪是为行星原位研究而设计的。该方法基于化学深度剖面，允许识别嵌入在围岩中的微米级包裹体，该包裹体在大部分样品中具有不同的成分。使用光谱清理程序改进用于精确同位素测量的数据，确保去除低质量的光谱。此外，一种元素的同位素相关性用于识别和拒绝不属于感兴趣物种的数据点。测量采用红外飞秒激光辐照，聚焦在样品表面，光斑大小约为12μm。对预定义数量的激光束进行材料去除，并记录每个烧蚀层的飞行时间质谱。测量是在NIST SRM 986镍同位素标准、三叠石矿物和嵌入文石中的微米级包裹体上进行的。我们的测量表明，元素同位素比率可以在permille水平上精确测量，例如B、Mg和Ni元素同位素的分析。所采用的方法将用于行星表面样品的现场调查，用于精确量化由过去或现在的生命或地球化学过程引起的元素分馏。

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