Abstract

Compound specific 13C/12 C analysis by gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) is widely employed to establish the provenance or history of samples. Applications include reconstructing ancient habitats in biogeochemistry, authenticating foods and flavors and determining food webs or migratory patterns. GC-C-IRMS is now routine for distinguishing exogenous and endogenous steroids in athletic doping detection. In this application, the time required for instrumental analysis is limiting, and the GC-C-IRMS is used primarily as a confirmatory test after a GC/MS screen detects an anomaly. Fast GC-C-IRMS holds the potential to enable analysis of all samples, and thus detect doping in samples for which the molecular marker concentrations have returned to normal. Narrow-bore fast GC columns (0.10-0.20 mm i.d. columns) can achieve up to 10-fold faster run times than conventional GC columns (0.25-0.32 mm i.d.), but this speed can only be achieved with fast detectors (e.g. flame ionization detector (FID) or time-of-flight mass spectrometry (TOF-MS). An added advantage of fast GC is improved detection limits due to diminished band broadening of the eluting peak. Despite the obvious advantages, the successful coupling of fast GC to IRMS has not been reported. Sessions has correctly noted that fast GC-C-IRMS may not be possible with commercial systems because fast GC demands a fast detector response that is incompatible with the high impedance feedback resistors. At least as importantly, the post-column combustion interface is known to broaden eluting peaks considerably. In this work, we address and comprehensively evaluate these issues and develop a fast GC-C-IRMS system. We demonstrate fast GC-C-IRMS on ten underivatized steroids for eventual application to urinary steroid analysis. Aus der Einleitung (geändert)