New methods for the robust analysis of lipids by coupling thin-layer chromatography with mass spectrometry

• Applicants: Privatdozent Dr. Jürgen Schiller; Dr. Claudia Wiesner
• Subject Area: Analytical Chemistry
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 531487925

Lipids are important biomolecules occurring in relatively high concentrations in all biological tissues, body fluids as well as food. The increasing knowledge about the key physiological functions of some lipids (for instance during the pathogenesis of selected diseases) has also fostered the interest in the accurate analysis of lipids. Due to the complex composition of lipid mixtures, a combination between chromatographic separation and mass spectrometry (MS) detection is typically used in "lipidomics" studies. Nevertheless, thin-layer chromatography (TLC) is another, more traditionally applied method of lipid analysis, which provides many important advantages. For instance, "memory effects" can be completely avoided (a new stationary phase is used in each experiment) and TLC is very eco-friendly because only small amounts of solvents have to be used.Unfortunately, detailed lipid analysis is not possible if TLC separation is combined with optical detection: the separation of the individual lipid classes can be easily achieved by means of TLC but the determination of the (normally different) fatty acyl residues is normally not possible. For that reason, TLC separation is increasingly combined with MS detection. The combination of these two techniques enables the evaluation of the fatty acyl composition of the different lipid classes. MALDI (Matrix-assisted Laser Desorption & Ionization) und ESI (Electrospray Ionization) were so far used as the primary ionization techniques. Both methods exhibit characteristic advantages and disadvantages towards the analysis of the individual lipid classes. Regarding quantitative analysis of the mass spectra, however, it is not yet clear which method provides optimum results.In this proposal, we would like to analyze lipid mixtures with different complexity, i.e. mixtures of known lipids and extracts of biological samples. Subsequent to TLC separation, the amounts of the individual lipid fractions will be analyzed by different MS techniques. In addition to MALDI and ESI, DESI (Desorption Electrospray Ionization) and a newly developed plasma desorption technique will be applied. Our aim is to identify the most suitable technique and to elucidate the reasons for the potential failing of other methods. The position of the sample within the stationary phase (in an "upper" or "deeper" layer) presumably plays a central role if surface desorption techniques are used. Thus, the spatial distribution of the analyte within the stationary phase will be also determined and the depth correlated with the extraction yield.The successful completion of these aims will help in the further establishment of TLC/MS for easy and reliable analysis of clinical samples. Of course, this also applies for food and samples from food processing. In a methodological sense, our results will advance the implementation of modern ionization techniques such as plasma-related techniques.

• DFG Programme: Research Grants