High resolution ion mobility-mass spectrometry for separation and identification of isomeric lipids

Lipidomics is a particularly difficult analytical challenge due to the number and importance of isomeric species that are known or postulated in biological samples. Current separation and identification techniques are too often insufficiently powerful, slow or ambiguous. High resolution, low field ion mobility coupled to mass spectrometry is shown here to have sufficient performance to represent a new alternative for lipidomics. For the first time, drift-tube ion mobility separation of lipid isomers that differ only in position of the acyl chain, position of the double bond or double bond geometry is demonstrated. Differences in collision cross sections of less than 1% are sufficient for baseline separation. The same level of performance is maintained in complex biological mixtures. More than 130 high-precision reduced mobility and collision cross section values were also determined for a range of lipids. Such data can be the basis of a new lipidomics workflow, as the appropriate libraries are developed.