Nontargeted Screening Using Gas Chromatography–Atmospheric Pressure Ionization Mass Spectrometry: Recent Trends and Emerging Potential

Gas chromatography-high-resolution mass spectrometry (GC-HRMS) is a powerful nontargeted screening technique that promises to accelerate the identification of environmental pollutants. Currently, most GC-HRMS instruments are equipped with electron ionization (EI), but atmospheric pressure ionization (API) ion sources have attracted renewed interest because: (i) collisional cooling at atmospheric pressure minimizes fragmentation, resulting in an increased yield of molecular ions for elemental composition determination and improved detection limits; (ii) a wide range of sophisticated tandem (ion mobility) mass spectrometers can be easily adapted for operation with GC-API; and (iii) the conditions of an atmospheric pressure ion source can promote structure diagnostic ion-molecule reactions that are otherwise difficult to perform using conventional GC-MS instrumentation. This literature review addresses the merits of GC-API for nontargeted screening while summarizing recent applications using various GC-API techniques. One perceived drawback of GC-API is the paucity of spectral libraries that can be used to guide structure elucidation. Herein, novel data acquisition, deconvolution and spectral prediction tools will be reviewed. With continued development, it is anticipated that API may eventually supplant EI as the de facto GC-MS ion source used to identify unknowns.