Coupling Gas Chromatography to FI-MS

In the early 1970s, the coupling of gas chromatography (GC) to FI-MS suffered from poor instrument capabilities of that time [84,85]. Recent advances with oaTOF instrumentation allow for fast acquisition of spectra, high resolution, and straightforward accurate mass measurements in GC-FI-MS. Thus, GC-FI-MS has become a trusted tool in many laboratories, especially in the petroleum industry [31,32,86,87]. To maintain full ionization efficiency, it is common that an accumulation period of 1 s per spectrum is followed by flash-heating the emitter for 0.1-0.2 s [31,32]. These applications have also been driving the development of EI/Fl/FD [39] and EFCI/FI combination sources for GC-oaTOF instruments [88]. 

FD can be regarded the softest ionization method in mass spectrometry, even though electrospray ionization and matrix-assisted laser desorption ionization can transfer much larger ions into the gas phase [27,89], This is mainly because the ionization process itself does not transfer any extra energy to the incipient ions. Problems normally arise above molecular weights of 3000 u where the heated emitter causes thermal decomposition of the saiiple. 

Example The extraordinarily stable trityl ion, PhsC, m/z 243, tends to dominate mass spectra (Chap. 6.6.2). Thus, neither the El spectrum of chlorotriphenylmethane nor that of its impurity triphenylmethanol show molecular ions 

Example D-Glucose evaporates into the ion source without conplete decomposition as demonstrated by its H spectrum (Fig. 8.13). HD yields a spectrum with a very low degree of fragmentation that is most probably due to the required slight 

Analytes of very high polarity are not further ionized by field ionization. Here, the prevailing pathways are protonation or cationization, i.e., the attachment of alkali ions to molecules [93]. The subsequent desorption of the ions from the surface is effected by the action of the electric field. As [M+Na] and [M+K] ions are already present in the condensed phase, the field strength required for their desorption is lower than that for field ionization or field-induced [M+H] ion formation [43,94]. The desorption of ions is also effective in case of ionic analytes. 

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