Higher dimensional separation methods based on the hyphenation of soft ionization methods with one- and two-dimensional chromatographic systems
M. Eschner (HMGU/UR), T. Gröger (HMGU/UR), M. Gonin (TOFWerk), K. Fuhrer (TOFWerk) R. Zimmermann (UR/HMGU)
- Fig. 1: Comparison of two-dimensional separation of diesel fuel using GCxGC (upper graph) and GCxMS (lower graph). Red: aliphatic hydrocarbons, yellow: monoaromatic hydrocarbons, green: polyaromatic hydrocarbons
For analysis of complex samples the coupling of analytical separation methods and spectrometric detection techniques is quite common. Gas chromatography (GC) is a well-established standard technique for volatile and semi-volatile organic compounds. In many cases mass spectrometry (MS) is used as detection unit for GC analysis. For ionization mainly electron ionization (EI) is applied. Most organic compounds are fragmented thereby showing a characteristic pattern which is used for identification. Particularly for highly fragile compounds, e.g. derivatized biological compounds, compound assignment is infeasible due to the missing molecular mass peak in the mass spectra. In addition, for highly complex samples, e.g. mineral oil fractions or aerosol extracts the separation power of conventional GC-MS techniques is not sufficient. For such separation challenge two approaches exist: Improvement of separation power of the chromatographic system or enhancement of the selectivity of the detection method.
(Kopie 2)
- Fig. 2: Three-dimensional GCxGCxMS chromatogram of a diesel fuel sample. With this approach the opportunity of separation power in three orthogonal dimensions is given (red: aliphatic carbon hydrates, green: alkylated benzoles, yellow: polyaromatic carbon hydrates)
[Translate to Englisch:] Within this project both approaches are pursued. The first approach is realized by application of comprehensive two-dimensional gas chromatography (GCxGC). An increase in selectivity of the mass spectrometric system can be achieved by adoption of single photon ionization (SPI). Compared to EI, the SPI process prevents (almost) entirely any fragmentation since the energy which is delivered to the analytes in terms of vacuum ultraviolet (VUV) light is in the range of 8 to 11 eV being marginally above the ionization energy of most organic compounds. This kind of ionization is also particularly used for online-measurements, in which a gaseous mixture is analyzed without preceding separation step. In this connection mass spectrometry is utilized as separation method. By coupling of SPI-MS to a GCxGC-system the analytical separation space is enhanced to three dimensions (Fig.2). Analytes which are not separated by comprehensive GCxGC can now be differentiated based on their molecular mass upon the mass axis.
