Brenna J T, Corso T N, Tobias H J, Caimi R J
Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, USA.
Mass Spectrom Rev. 1997 Sep-Oct;16(5):227-58. doi: 10.1002/(SICI)1098-2787(1997)16:5<227::AID-MAS1>3.0.CO;2-J.
Although high-precision isotope determinations are routine in many areas of natural science, the instrument principles for their measurements have remained remarkably unchanged for four decades. The introduction of continuous-flow techniques to isotope ratio mass spectrometry (IRMS) instrumentation has precipitated a rapid expansion in capabilities for high-precision measurement of C, N, O, S, and H isotopes in the 1990s. Elemental analyzers, based on the flash combustion of solid organic samples, are interfaced to IRMS to facilitate routine C and N isotopic analysis of unprocessed samples. Gas/liquid equilibrators have automated O and H isotopic analysis of water in untreated aqueous fluids as complex as urine. Automated cryogenic concentrators permit analysis at part-per-million concentrations in environmental samples. Capillary gas chromatography interfaced to IRMS via on-line microchemistry facilitates compound-specific isotope analysis (CSIA) for purified organic analytes of 1 nmol of C, N, or O. GC-based CSIA for hydrogen and liquid chromatography-based interfaces to IRMS have both been demonstrated, and continuing progress promises to bring these advances to routine use. Automated position-specific isotope analysis (PSIA) using noncatalytic pyrolysis has been shown to produce fragments without appreciable carbon scrambling or major isotopic fractionation, and shows great promise for intramolecular isotope ratio analysis. Finally, IRMS notation and useful elementary isotopic relationships derived from the fundamental mass balance equation are presented.
尽管高精度同位素测定在自然科学的许多领域已成为常规操作，但用于测量的仪器原理在过去四十年中却几乎没有变化。20世纪90年代，连续流技术引入同位素比率质谱仪（IRMS），促使对碳、氮、氧、硫和氢同位素进行高精度测量的能力迅速扩展。基于固体有机样品快速燃烧的元素分析仪与IRMS相连，便于对未处理样品进行常规碳和氮同位素分析。气体/液体平衡器实现了对尿液等复杂未处理水性流体中水分的氧和氢同位素自动分析。自动低温浓缩器可对环境样品中百万分之一浓度的成分进行分析。通过在线微化学与IRMS相连的毛细管气相色谱法，有助于对1 nmol碳、氮或氧的纯化有机分析物进行化合物特异性同位素分析（CSIA）。基于气相色谱的氢CSIA和基于液相色谱与IRMS的联用均已得到验证，持续的进展有望使这些技术得到常规应用。使用非催化热解进行的自动位置特异性同位素分析（PSIA）已证明可产生无明显碳重排或主要同位素分馏的片段，在分子内同位素比率分析方面前景广阔。最后，介绍了IRMS的表示法以及从基本质量平衡方程推导得出的有用基本同位素关系。
