Integration of Continuous-Flow Accelerator Mass Spectrometry with Chromatography and Mass-Selective Detection

Physical combination of an accelerator mass spectrometry (AMS) instrument with a conventional gas chromatograph−mass spectrometer (GC/MS) is described. The resulting hybrid instrument (GC/MS/AMS) was used to monitor mass chromatograms and radiochromatograms simultaneously when¹⁴C-labeled compounds were injected into the gas chromatograph. Combination of the two instruments was achieved by splitting the column effluent and directing half to the mass spectrometer and half to a flow-through CuO reactor in line with the gas-accepting AMS ion source. The reactor converts compounds in the GC effluent to CO₂ as required for function of the ion source. With cholesterol as test compound, the limits of quantitation were 175 pg and 0.00175 dpm injected. The accuracy achieved in analysis of five nonzero calibration standards and three quality control standards, using cholesterol-2,2,3,4,4,6-d₆ as injection standard, was 100 ± 11.8% with selected ion monitoring and 100 ± 16% for radiochromatography. Respective values for interday precision were 1.0−3.2 and 22−32%. Application of GC/MS/AMS to a current topic of interest was demonstrated in a model metabolomic study in which cultured primary hepatocytes were given [¹⁴C]glucose and organic acids excreted into the culture medium were analyzed.