FORMATION OF LITHIATED ADDUCTS OF GLYCEROPHOSPHOCHOLINE LIPIDS FACILITATES

电喷雾电离（ESI）串联质谱（MS）具有 磷脂混合物的简化分析，和，在负离子 模式，允许结构鉴定皮摩尔量的 磷脂种类。 碰撞活化解离（CAD） 磷脂阴离子产生负离子串联质谱， 含有代表脂肪酸取代基的碎片离子， 羧酸根阴离子。 甘油磷酸胆碱（GPC）脂质含有 季氮部分和更容易形成阳离子加合物比 质子化的阴离子种类和正离子串联质谱 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，GPC物种的锂化加合物 通过向溶液中加入氢氧化锂， 该磷脂混合物被注入ESI源。 的计算机辅助设计 [MLi GPC物质的+]离子产生串联质谱，其包含 代表脂肪酸损失的主要离子 替代品 可以使用这些离子及其相对丰度 指定脂肪酸取代基的身份和位置 GPC物种 串联质谱扫描监测中性 从锂化中损失头基或脂肪酸取代基 加合物可用于鉴定组织磷脂中的GPC物质 混合物。 类似扫描监测特定产物离子的母体 也可用于鉴定GPC的脂肪酸取代基 物种，这有利于识别不同的等压 在ESI/MS总离子电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.