Targeted Metabolomics with DSI-GC-MS - Rapid Profiling of Fatty Acids in Baker's Yeast

Helmut Geppert, Central Analytical Laboratory, Brandenburg University of Technology, D-03046 Cottbus, Germany
Thomas Fischer, Central Analytical Laboratory, Brandenburg University of Technology , D-03046 Cottbus, Germany

A Direct Sample Introduction Device (DSI) for mass spectrometry studies and GC-MS analysis was introduced by Amirav and Dagan in 1997. The device can serve as an introduction device for dirty untreated samples in any form of liquid, solid, powder or slurry. These include also body fluids and other human matrices such as urine, blood or plasma, hair, tissues and bacteria. The DSI eliminate, or significantly reduce the sample preparation steps of extraction, clean up and preconcentration, and allow in-vial analytical derivatization.
To our knowledge, this is the first study to demonstrate that the DSI can be used for the rapid profiling of fatty acids in baker's yeast. The method incorporates an fast in-vial sample silylation of the R-COOH (and alkyl–OH) groups with MTBSTFA.
The following figure shows a comparison of the GC-MS chromatogram for the determination of fatty acids in baker’s yeast extract with the standard method (alkaline saponification, methylation with methanol/HCl and extraction ) and the new DSI-method (alkaline saponification, extraction and in-vial silylation with MTBSTFA).

Figure: comparison of the GC-MS chromatogram for the determination of fatty acids in
baker’s yeast(below standard method, above new DSI method)

As can be seen from the figure, the same fatty acid distribution results for both methods. But using the new method, it can be derivatized directly in the injector of the GC and the EI-MS-spectrum shows [M-57]-fragments as base peak. This is of great advantage particularly in the examination of very small sample sizes (e.g. tissue cuts for the microscopic examination).