Lipidomics, as a branch of metabolomics, that was first introduced in 2003. In comparison to the study of individual lipid(s), lipidomics aims for the examination of global lipid metabolits in a given system. Thus, it follows, in general terms, the untargeted metabolomics approach.
After extraction of lipids from a biological sample, an internal standard is added to the extract. The sample is separated by liquid chromatography and analysed in an untargeted way (Full-Scan and data dependent MS2) using high resolution mass spectrometry.
As lipids display a great diversity in chemical structure and have distinct chemical properties, the analysis of lipidomics data, especially their annotation, is a complex task.
The first step in such an annotation is the extraction of peaks formed by molecules of one particular mass-to-charge ratio. In the following, this m/z-values are utilized to annotate each peak with an atomic composition. Unfortunately, it is not sufficient to reveal the particulate fatty-acyl side chains on a lipid based on this measurement. To achieve this information, the presumed lipid molecules have to be fragmented. Dissociating the fatty-acyl side chains and the head group from the glycerol backbone and afterwards measure the m/z values of these fragments, an annotation of the initial peak is possible.
Other structural details of the lipid, such as double bond type and position and the position of hydroxyl group modifications cannot be detected using this method.