FORMATION OF LITHIATED ADDUCTS OF GLYCEROPHOSPHOCHOLINE LIPIDS FACILITATES

电喷雾电离(ESI)串联质谱仪 磷脂混合物的简化分析，以及在负离子中 模式，允许对皮摩尔量的结构进行识别 磷脂物种。碰撞活化解离(CAD) 磷脂阴离子产生负离子串联质谱图 包含代表脂肪酸取代基的碎片离子 羧酸盐阴离子。甘油磷胆碱(GPC)脂类含有 并更容易形成阳离子加合物，而不是 质子化产物的阴离子物种和正离子串联质谱图 GPC物种不含丰富的识别脂肪酸的离子 取代基。我们在这里报告了GPC物种的锂加合物 很容易通过在溶液中加入氢氧化锂而形成 将哪些磷脂混合物注入ESI源。计算机辅助设计 GPC物种的[MLI+]离子产生串联的质谱图，其中包含 代表脂肪酸损失的显著离子 辅助者。这些离子及其相对丰度可以用来 指认脂肪酸取代基的结构和位置 GPC种。串联质谱学扫描监测中性 锂离子的头基团或脂肪酸取代基的损失 加合物可用于鉴定组织磷脂中GPC的种类 混合物。监测特定产物离子亲本的类似扫描 也可用于鉴定GPC的脂肪酸取代基 物种，这有助于鉴别不同的同位异构体 ESI/MS总离子流中观察到的离子的贡献者。

Electrospray ionization (ESI) tandem mass spectrometry (MS) has simplified analysis of phospholipid mixtures, and, in negative ion mode, permits structural identification of picomole amounts of phospholipid species. Collisionally activated dissociation (CAD) of phospholipid anions yields negative ion tandem mass spectra that contain fragment ions representing the fatty acid substituents as carboxylate anions. Glycerophosphocholine (GPC) lipids contain a quaternary nitrogen moiety and more readily form cationic adducts than anionic species, and positive ion tandem mass spectra of protonated GPC species contain no abundant ions which identify fatty acid substituents. We report here that lithiated adducts of GPC species are readily formed by adding lithium hydroxide to the solution in which phospholipid mixtures are infused into the ESI source. CAD of [MLi+] ions of GPC species yields tandem mass spectra that contain prominent ions representing losses of the fatty acid sub stituents. These ions and their relative abundances can be used to assign the identities and positions of the fatty acid substituents of GPC species. Tandem mass spectrometric scans monitoring neutral losses of the head-group or of fatty acid substituents from lithiated adducts can be used to identify GPC species in tissue phospholipid mixtures. Similar scans monitoring parents of specific product ions can also be used to identify the fatty acid substituents of GPC species, and this facilitates identification of distinct isobaric contributors to ions observed in the ESI/MS total ion current.