The coupling of a gas chromatograph (GC) to a mass spectrometer (MS) results in the marriage of two powerful technologies. The tremendous separative power of the GC is coupled to the direct identification and quantitation capabilities of the MS. The MS produces ions by electron bombardment of eluted compounds and the subsequent decomposition of these ions is monitored. The observed fragmentation patterns or “mass spectra” have characteristic ions that can be selectively monitored to obtain enhanced sensitivity for quantitative studies. This selected ion monitoring (SIM) is most accurately termed “gas chromatography-mass fragmentography (GC-MF).”