Better screening of non-target pollutants in complex samples using advanced chromatographic and mass spectrometric techniques

The number of priority and emerging contaminants nowadays exceeds several thousands. As a consequence, it is a daunting task to monitor thousands of compounds using classical gas chromatography-mass spectrometry (GC-MS). Preliminary non-targeted screening is thus usually performed to identify the most relevant contaminants. Here we analyzed complex environmental samples of snow, rain water and cloud water from the Arctic, France, Chile, and Russia by two-dimensional gas chromatography (GC x GC) with ionization methods including electron ionization (EI), positive chemical ionization (PCI), and electron capture negative ionization (ECNI) modes, combined with high-resolution mass spectrometry. This approach combines the separation capacity of GC x GC, detailed EI mass spectral libraries, the softness of PCI, and the selectivity of ECNI. Switching between ionization modes without any hardware change allowed to increase the information capacity and reliability of analysis. The structural elucidation becomes easier and more reliable due to the detection of molecular ions in PCI and ECNI modes with corresponding extensive fragmentation in EI, while the ECNI mode improves about 100 times the detection limits for environmentally relevant halogenated and nitro compounds. Overall, a notable enhancement of the analytical capabilities for both targeted and non-targeted purposes is achieved.