Rapid 18O analysis of small water and CO2 samples using a continuous-flow isotope ratio mass spectrometer

Rapid Commun Mass Spectrom. 2002;16(13):1257-60. doi: 10.1002/rcm.711.


High-frequency throughput is often needed in isotopic studies in biological and medical fields. Here we report that high-precision oxygen isotope ratio measurements of water (+/-0.13 per thousand) were rapidly and routinely made on small samples (40-100 microL) using an isotope ratio mass spectrometer operated in continuous-flow mode. Simple modifications to existing instrumentation allow for rapid manual analyses of dilute CO2 (10% CO2/90% N2), including the addition of a septum port and water trap prior to the gas chromatography (GC) column (elemental analyzer column in this study) and the extension of fused-silica capillary tubing between the mass spectrometer source and the effluent tubing from the GC column (located within the CONFLO unit on Finnigan mass spectrometers). We routinely analyzed 20 small-volume samples per hour using this technique, without sacrificing precision of the oxygen isotope ratio measurement.

MeSH terms

  • Carbon Dioxide / chemistry*
  • Fresh Water / chemistry*
  • Mass Spectrometry / instrumentation
  • Mass Spectrometry / methods*
  • Oxygen Isotopes / analysis*
  • Reproducibility of Results
  • Sensitivity and Specificity


  • Oxygen Isotopes
  • Carbon Dioxide