I. Introduction 332 II. Techniques and Methods 334 A.  Sample Preparation 334 B.  ESI‐MS/MS 336     1.  Glycerophosphocholine (GPCho) Lipids 336     2.  Sphingomyelin 341     3.  Glycerophosphoethanolamine (GPEtn) Lipids 342     4.  Glycerophosphatidic Acid (GPA) Lipids 344     5.  Glycerophosphoinositol (GPI) Lipids 346     6.  Glycerophosphoglycerol (GPGro) Lipids 349     7.  Glycerophosphoserine (GPSer) Lipids 349     8.  Cardiolipin 351 C.  Matrix‐Assisted Laser Desorption/Ionization (MALDI) Analysis 353 D.  Precursor‐Ion and Neutral‐Loss Scanning 353 E.  Quantitation 355 III. Research Applications 356 IV. Conclusion 359 Acknowledgments 360 Abbreviations 360 References 360

Phospholipids play a central role in the biochemistry of all living cells. These molecules constitute the lipid bilayer defining the outer confines of a cell, but also serve as the structural entities which confine subcellular components. Mass spectrometry has emerged as a powerful tool useful for the qualitative and quantitative analysis of complex phospholipids, including glycerophospholipids and the sphingolipid, sphingomyelin. Collision induced decomposition of both positive and negative molecular ion species yield rich information as to the polar head group of the phospholipid and the fatty‐acyl substituents esterified to the glycerophospholipid backbone. This review presents the current level of understanding of the mechanisms involved in the formation of various product ions following collisional activation of molecular ion species generated by electrospray ionization of the common glycerophospholipids, including phosphatidic acid, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, phosphatidylglycerol, phosphatidylserine, cardiolipin, and sphingomyelin. Recent advances in the application of matrix assisted laser desorption ionization is also considered. Several applications of mass spectrometry applied to phospholipid analysis are presented as they apply to physiology as well as pathophysiology. © 2003 Wiley Periodicals, Inc., Mass Spec Rev 22:332–364, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mas.10061