Mass profile monitoring in trace analysis by gas chromatography/mass spectrometry

The advantages of gas chromatography/mass spectrometry (GC/MS) selected-ion monitoring (SIM) in the mass profile (MP) mode at medium mass resolving power were investigated for analyses requiring detection of low-picogram quantities of analytes in complex mixtures. The mass profile monitoring provides a certainty at least 10 times greater than that achieved by conventional GC/MS-SIM in the peak-top monitoring mode, and it can be operated at lower mass resolving power to compensate for the loss of sensitivity in the MP mode. The examination of mass profile peak shape, central mass shift, and sequential changes during GC elution not only reveals the presence of interfering compounds but also results in accurate mass measurement for those interferences. The latter feature takes the MP mode beyond the target mass analysis that GC/MS-SIM was originally designed for. This additional dimension of information is particularly useful for those complex and incompletely characterized matrices that are frequently encountered in environmental and biological sample analyses.