Abstract
GC-MS with Cold EI improves all of the central GC-MS performance aspects, but it is known mostly for its provision of enhanced molecular ions. This occasionally leads to the misconception that, like chemical ionization, Cold EI is a supplementary ion source to standard EI. However, Cold EI is a highly superior replacement ion source to standard EI. While Cold EI mass spectra are the most informative and fully compatible with mass spectral library (such as NIST) identification, in some cases, the Cold EI mass spectra with their enhanced molecular ions result in a "picture" that is not as one is used to seeing. In this paper, we describe the "Cool Classical EI" mode, which produces classical EI mass spectra like standard EI. The change of Cold EI into the Cool Classical EI mode is software-based, requires no hardware change, and can be achieved even during the analysis. Several mass spectra that were obtained in the Cool Classical EI mode are presented and compared with standard EI and Cold EI mass spectra. In this paper we further demonstrate and discuss several benefits that Cold EI brings that are retained while using Cool Classical EI, including (a) much faster speed of analysis, (b) uniform response, (c) extended range of compounds amenable for analysis, (d) improved sample identification, (e) elimination of ion source related peak tailing, (f) elimination of intraion-source degradation, and (g) better signal-to-noise ratio of the sample compounds.