Abstract
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.
Highlights
Chemistry is essential to the modern world, producing molecules and materials required in all facets of society
Concerns that some of these chemicals can persist in the environment, bioaccumulate and adversely impact human health have led to international efforts to restrict theintentional release of 28 groups of hazardous chemicals, i.e., persistent organic pollutants (POPs) [4]
We summarize the recent developments and applications of GC–atmospheric pressure ionization (API) reported during the last five years, using SciFinder with the keywords “GC–atmospheric pressure chemical ionization (APCI)”, “APGC”, “GC–Atmospheric Pressure Photoionization (APPI)”, “GC–atmospheric pressure laser ionization (APLI)” or “GC–electrospray ionization (ESI)”
Summary
Chemistry is essential to the modern world, producing molecules and materials required in all facets of society. Gas chromatography– and liquid chromatography–high-resolution mass spectrometry (GC–HRMS and LC–HRMS) are powerful, complementary techniques for NTS of persistent and bioaccumulative organic pollutants The need for both techniques is underlined by the results of a recent interlaboratory study led by Rostkowski et al [7,8]. Extensive fragmentation under EI conditions can produce mass spectra in which the molecular ion is absent, thereby confounding elemental composition determination and structure elucidation This drawback can potentially be solved by lowering the electron energy in EI or using other vacuum ionization techniques such as chemical ionization (CI) [10], photoionization (PI) [11] and field ionization (FI) [12], which impart significantly less energy to the analyte molecules. Our contribution will instead focus on the application of various GC–API techniques to identify unknown pollutants, as well as the computational techniques being developed to predict mass spectra and aid in the interpretation of NTS data
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