Targeted versus Untargeted Lipidomics (Assays)
"Targeted" assay is where the lipid species to be analyzed is already labeled and known before the analysis process. An example is multiple reaction monitoring method, which has "excellent sensitivity and is ideal for accurate quantitation" (1). Through this method, the researcher only finds what he is looking for.
"Untargeted" assay is more of a discover as you research type of assay of lipids. An example of this assay is using the mass spectrometer in full-scan mode, which searches for new mass-to-charge ratio peaks. This method has assumptions such as that the species will ionize efficiently and that the mass spectrometer is sensitive. Furthermore, after a new, novel lipid is discovered, further investigation and research can be conducted on the newly observed lipid. There is a concern/question that arises while conducting untargeted assays, such as are biologically significant lipid species being overlooked?
There are many examples of novel, unexpected lipids, such as the discovery of the concept of fatty acids by Michael Eugene Chevreul. He was the first lipid specialist to discover the concept of fatty acids and also discovered cholesterol and glycerol. Other examples of novel lipids include the "novel family of N-acylphosphoserine derivatives in the brain of a mouse and also glycoerophosphocholine in retina of the eye" (1).
== Reference ==
1. Annu Rev Biochem. 2011 Jun 7;80:301-25. Applications of mass spectrometry to lipids and membranes.