Comprehensive two-dimensional gas chromatography-mass spectrometry using milder electron ionization conditions: A...

The present research is based on the use of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-QMS), using "milder" electron ionization (EI) conditions. The term milder refers to the use of lower energy EI conditions (e.g., 20 eV), instead of the most common electron energy of 70 eV. The effects of using lower source temperatures were also evaluated. Within such an analytical context, GC × GC-QMS was applied to the analysis of a variety of different molecular-mass compounds with various polarities (sterols, linear alkanes, fatty acid methyl esters, vitamin E, squalene, a linear alcohol, and a group of fifteen pesticides). In general, the results attained indicate that milder EI conditions, and lower source temperatures, generate mass spectra with a higher relative abundance of ions at higher mass-over-charge (m/z) values, comprising the molecular ion, and reduced fragmentation at lower m/z values. The extent to which such a phenomenon occurred was obviously related to the chemical structure of each analyte. Spectral repeatability was also assessed, and was found to be satisfactory. Finally, with regard to analyte signal-to-noise ratios these were generally comparable in applications involving different electron ionization energies.