Biochemical Applications of High Precision Isotope Analysis by Combined Gas Chromatography-Mass Spectrometry

Abstract

When labelled sugars are produced by in vivo photosynthesis in the presence of ¹³CO₂ the resulting material is often a combination of at least two types of isotopic species, the endogenous material containing ¹³C in natural abundance and the enriched material. Before such materials can be used in clinical applications where quantitative studies are being carried out, it is necessary to determine the enrichment of the various isotopic components. The analyses described in this work were designed to measure: 1. The relative amounts of unenriched and uniformly labelled material. 2. The uniformity of the ¹³C label in the enriched material. 3. The enrichment in the labelled material. These measurements were done with a combined gas chromatographmass spectrometer (GC-MS) operating in the selected ion monitoring mode. This technique is especially useful for isotopic analyses because it can be successfully used to obtain quantitative data even on microgram quantities of complex mixtures.