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An overview

Electron impact ionization

In the analytical metrology the combination gas-chromatography/mass spectrometry has been used successfully for decades.

In view of the measuring sensitivity and the identification of the components to be analyzed the standard measuring technique electron impact ionization (electron impact/EI) offers extraordinary possibilities. The size of the mass spectral reference libraries increases from year to year. Currently mass spectral libraries with more than 350.000 entries are commercially offered. The measuring sensitivity has thus been improved, that analyte concentrations of 1pg/pL -1Opg/pL are recorded by means of the full scan analysis. Nevertheless some demands on the metrology remain open, if e.g. the electron impact spectrum gives no, or only insufficient information about the molar mass of the analyte, or if with matrix loaded sample quality the selectivity isn't adequate and the response therefore decreases drastically.

Chemical ionization

With the techniques of the "chemical ionization" (CI) there are methods available for such cases which extend the use of the mass spectral detection significantly. With the method of the "positive chemical ionization" (PCI) the molar ions in the mass spectrum are increased by the selection of suitable reactant gases, significant adducts confirm the molar mass of the analyte. The "negative chemical ionization" (NCI) offers for components, which are known for their high electron affinity, the possibility to measure selectively and extremely sensitively. Detection concentrations of femtogram per microlitre are easily possible.

With the method of the CI the mass spectrometry is being used individually, i.e. problem-oriented.

Constant measuring parameters guarantee a high consistency.

Electron impact ionization