Living Reference Work Entry

Encyclopedia of Geochemistry

Part of the series Encyclopedia of Earth Sciences Series pp 1-4

Date: Latest Version

Compound-Specific Isotope Analysis

  • Yi Ge ZhangAffiliated withDepartment of Oceanography, Texas A&M University Email author 

Definition

Compound-specific isotope analysis (CSIA), as opposed to bulk analysis, determines the isotopic signatures (for example, 13C/12C, D/H, 15N/14N, 18O/16O) at the molecular level. The separation and purification of organic compounds can be achieved by gas chromatography (GC) or liquid chromatography (LC). The analysis of stable isotopes requires an isotope ratio mass spectrometry (IRMS).

Analytical Methods: GC-IRMS

Traditionally, CSIA refers only to the stable isotope measurements of the molecules separated by GC. The system usually consists of a GC, a chemical reaction interface, and an IRMS (Sessions 2006; Summons 2000). Individual compounds are separated by the GC, followed by quantitative conversion at the interface, and continuous-flow isotopic analysis using the IRMS. The interface either diverts or removes the interfering compounds such as the solvents and H2O.

Early CSIA focused on stable carbon ...

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