作者:D. J. Harvey
DOI:10.1002/jms.1190300918
日期:1995.9
Phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, phosphatidylinositol, phosphatidic acid and cardiolipin were examined by matrix-assisted laser desorption/ionization mass spectrometry on both a time-of-flight and a magnetic sector instrument using several substituted cinnamic acids, benzoic acids and substituted coumarins as matrices. All of these phospholipids gave signals, with the strongest responses being obtained from α-cyano-4-hydroxycinnamic acid, esculetin (6,7-dihydroxycoumarin) and 2,5-dihydroxybenzoic acid (2,5-DHB). In the positive-ion mode, most compounds produced mixtures of [M + H]+, [M + Na]+ and [M + K]+ ions from both the free acids and from the sodium salts to give a complex mixture of ions. The spectra were considerably simpler in the negative-ion mode, where the molecular ion region contained mainly [M − H]− ions. Spectral simplification was also achieved in the positiveion mode by methylation with diazomethane to prevent salt formation. This procedure had the additional advantage of converting phosphatidylethanolamine and phosphatidylserine into their corresponding quaternary derivatives with a consequent gain in detection sensitivity. Fragmentation involving cleavages around the phosphate group was common, with the diacyl-containing ion produced by loss of the substituted phosphate moiety being particularly abundant. Fragmentation appeared to be strongly dependent on the nature of the matrix and, particularly, on the presence or absence of water in the matrix solvent. With spectra recorded on the magnetic sector instrument, additional fragment ions produced by losses of the acyl groups were seen. These latter ions provided some information regarding the distribution of carbon atoms between the acyl chains.
以几种取代的肉桂酸、苯甲酸和取代的香豆素为基质,在飞行时间和磁扇区仪器上进行了基质辅助激光解吸附/电离质谱分析,检验了磷脂、溶血磷脂酰胆碱、磷脂酰乙醇胺、磷脂酰丝氨酸、磷脂酰甘油、磷脂酰肌醇、磷脂酸和心磷脂。所有这些磷脂都发出了信号,其中反应最强的是α-氰基-4-羟基肉桂酸、香豆素(6,7-二羟基香豆素)和 2,5-二羟基苯甲酸(2,5-DHB)。在正离子模式下,大多数化合物都能从游离酸和钠盐中产生 [M+H]+、[M+Na]+ 和 [M+K]+ 离子的混合物,从而得到复杂的离子混合物。在负离子模式下,分子离子区主要包含[M - H]-离子,因此光谱要简单得多。在正离子模式下,还可以通过重氮甲烷甲基化来防止盐的形成,从而简化光谱。该方法的另一个优点是可将磷脂酰乙醇胺和磷脂酰丝氨酸转化为相应的季衍生物,从而提高检测灵敏度。磷酸盐基团周围的裂解碎片很常见,其中因失去取代的磷酸盐分子而产生的含二酰离子特别多。碎片似乎在很大程度上取决于基质的性质,特别是基质溶剂中是否含水。在磁扇区仪器上记录的光谱中,可以看到因酰基损失而产生的额外碎片离子。这些离子提供了一些有关酰基链之间碳原子分布的信息。