Direct Infusion Mass Spectrometry for Complex Lipid Analysis.

Direct infusion or "shotgun" mass spectrometry provides a fast strategy to measure different classes of lipids, combining rapid analysis and short idle time. In contrast to liquid chromatography-mass spectrometry (LC-MS), the lipids are infused into the mass spectrometer without prior separation by liquid chromatography. Ions are separated in the quadrupole of a tandem mass spectrometer, and after collision-induced dissociation fragments are quantified relative to internal standards in the third quadrupole or in the time-of-flight mass analyzer of a triple quadrupole or quadrupole time of flight (Q-TOF) mass spectrometer. Abundant lipids, that is, galactolipids and phospholipids in leaves, are measured in crude lipid extracts, while less abundant lipids can be measured after enrichment by solid-phase extraction. Here we describe protocols for the quantification of the major plant glycerolipids (galactolipids, phospholipids, diacylglycerol, and triacylglycerol) using nanospray direct infusion mass spectrometry. This provides a strategy for comprehensive, highly sensitive, high-throughput lipidomic analyses.