Gathering complementary molecular information within one GC-MS analysis by means of fast switching between electron-impact and single-photon ionization
M. Eschner (HMGU), T. Gröger (HMGU), R. Zimmermann (UR/HMGU)
It was demonstrated by means of a mineral oil distillate, that more information can
be gained from a single GC-MS analysis if the ionization process is switched fast between hard electron-impact and soft single-photon ionization. First attempts in the field of metabolomics were accomplished with derivatized biological relevant substances.
The hyphenation of gas chromatography with mass spectrometry (GC-MS) is a common method in the field of analytical chemistry. Usually the previously separated substances are ionized by electron-impact ionization (EI). This ionization technique causes fragmentation by which many organic compounds can be identified by comparison of their characteristic fragmentation pattern with mass spectra libraries. However, in some cases identification is hindered because of the lack of a molecular mass peak. This is the case especially for derivatized organic compounds. In contrast to EI single-photon ionization (SPI) predominantly leads to formation of molecular ions.
If both ionization techniques are combined in a single GC-MS analysis enhanced information about the sample can be gained. In this approach, a mineral oil distillate serving as test matrix, switching between both ionization techniques was realized with a frequency of 10 Hz. Therefore, a mass spectrum of each ionization method is obtained for a certain retention time. The GC-SPI-MS data can also be displayed in a two dimensional (2D) contour plot. This leads to a comprehensive two dimensional characterization of the sample (chromatographic x mass spectrometric dimension, GCxMS), whereas the typical group type assignment is also met. Furthermore, this switching approach was applied for the investigation of biological relevant substances.
- The total ion current (TIC) of a mineral oil sample (EI and SPI mode) as well as the mass spectrum of n-eicosane for both ionization techniques.
