MALDI-TOF-MS of Typical Lipid Mixtures

Although, to date, many different, physiologically relevant lipid mixtures (blood, Hpoproteins, cells, etc.) have been investigated using MALDI-MS, investigations with these mixtures are not always straightforward because (i) there is often only a quite Umited interest in a particular system (ii) the mixtures are normally very complicated and (iii) the experiments are often difficult to repeat because the systems discussed are not readily available. Hence, attention will be focused here on a simple system, namely an organic extract from hen egg yolk [117]. 

The corresponding lipid extracts can be easily obtained and with a high reproducibility different egg yolk extracts can be pooled and, thus, differences are averaged. 

Hen egg yolk is a rich source of PLs, where the individual PLs are present in totally different amounts. For instance, PC comprises about two-thirds of the total PL, while PI constitutes less than 1%. Consequently, the hen egg yolk extract serves as an excellent example to investigate dynamic range problems. 

2) The spectrum recorded in the presence of 9-AA (b) is much simpler to interpret because there are primarily the proton adducts of the individual PC species. This enables the direct assignments of the m/z values to the fatty acyl compositions, while this is much more difficult using DHB that leads to a mixture between and Na adducts. 

Although this may sound trivial, it is very important to note that the amounts of detected lipids depend heavily on the extraction process used. Despite this obvious link, however, very few reports have described the extraction process and, thus, the potential losses of Upids that may occur [120]. Hence, some comments on the extraction of aqueous samples (body fluids or tissues) in order to enrich 

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