Unequivocal assignment of phospholipid peaks in complex mixtures is difficult if only the m/z values but no tandem mass spectrometry (MS/MS) data are available. This is usually the case for matrix-assisted laser/desorption ionization time-of-flight (MALDI-TOF) MS imaging experiments and the analysis has normally to be performed without prior separation. Another problem might be the often matrix-induced loss of one methyl group in phosphatidylcholine (PC) species, which makes them detectable as negative ions becoming isomers of some phosphatidylethanolamines (PEs). Selected lipid mixtures of known compositions were investigated by negative ion MALDI-TOF MS and various imaging experiments. In addition to common matrices such as 2,5-dihydroxybenzoic acid (DHB) and 9-aminoacridine (9-AA), different binary matrices, including 2,5-dihydroxyacetophenone (2,5-DHAP) as matrix additive to DHB, were tested to probe their performance in both ionization modes. Beside artificial PC and PE mixtures of known compositions, egg yolk and liver extracts as well as cryosections from liver and pancreas tissue were selected as biologically relevant systems. The majority of the binary MALDI matrices used here leads to the loss of a methyl group from PC in the negative ion mode, which makes the clear identification of PE species ambiguous. However, this problem does not apply if a mixture of DHB and 2,5-DHAP is used. Therefore, the application of DHB/2,5-DHAP as matrix is a simple method to unequivocally identify PEs even in complex mixtures and tissue sections as negative ions and without the necessity to separate the individual lipid classes prior to MS detection.

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如果仅m / z，则难于明确区分复杂混合物中的磷脂峰值，但没有串联质谱（MS / MS）数据。基质辅助激光/解吸电离飞行时间（MALDI-TOF）MS成像实验通常是这种情况，并且分析通常必须在没有事先分离的情况下进行。另一个问题可能是基质引起的磷脂酰胆碱（PC）物种中一个甲基的丢失，这使得它们可以被检测为负离子成为某些磷脂酰乙醇胺（PEs）的异构体。通过负离子MALDI-TOF MS和各种成像实验研究了已知成分的选定脂质混合物。除了常见的基质（例如2,5-二羟基苯甲酸（DHB）和9-氨基ac啶（9-AA））之外，还存在其他不同的二元基质，包括2,5-二羟基苯乙酮（2,5-DHAP）作为DHB的基质添加剂，被测试以探测其在两种电离模式下的性能。除了已知成分的人造PC和PE混合物外，还选择了蛋黄和肝提取物以及来自肝和胰腺组织的冰冻切片作为生物学上相关的系统。此处使用的大多数二元MALDI矩阵会导致PC在负离子模式下丢失甲基，这使得对PE物种的清晰识别变得模棱两可。但是，如果使用DHB和2,5-DHAP的混合物，则不会出现此问题。因此，使用DHB / 2,5-DHAP作为基质是一种即使在复杂混合物和组织切片中也能明确鉴定PE为负离子的简单方法，并且无需在MS检测之前分离各个脂质类别。选择蛋黄和肝脏提取物以及来自肝脏和胰腺组织的冰冻切片作为生物学上相关的系统。此处使用的大多数二元MALDI矩阵会导致PC在负离子模式下丢失甲基，这使得对PE物种的清晰识别变得模棱两可。但是，如果使用DHB和2,5-DHAP的混合物，则不会出现此问题。因此，使用DHB / 2,5-DHAP作为基质是一种即使在复杂混合物和组织切片中也能明确鉴定PE为负离子的简单方法，并且无需在MS检测之前分离各个脂质类别。选择蛋黄和肝脏提取物以及来自肝脏和胰腺组织的冰冻切片作为生物学上相关的系统。此处使用的大多数二元MALDI矩阵会导致PC在负离子模式下丢失甲基，这使得对PE物种的清晰识别变得模棱两可。但是，如果使用DHB和2,5-DHAP的混合物，则不会出现此问题。因此，使用DHB / 2,5-DHAP作为基质是一种即使在复杂混合物和组织切片中也能明确鉴定PE为负离子的简单方法，并且无需在MS检测之前分离各个脂质类别。此处使用的大多数二元MALDI矩阵会导致PC在负离子模式下丢失甲基，这使得对PE物种的清晰识别变得模棱两可。但是，如果使用DHB和2,5-DHAP的混合物，则不会出现此问题。因此，使用DHB / 2,5-DHAP作为基质是一种即使在复杂混合物和组织切片中也能明确鉴定PE为负离子的简单方法，并且无需在MS检测之前分离各个脂质类别。此处使用的大多数二元MALDI矩阵会导致PC在负离子模式下丢失甲基，这使得对PE物种的清晰识别变得模棱两可。但是，如果使用DHB和2,5-DHAP的混合物，则不会出现此问题。因此，使用DHB / 2,5-DHAP作为基质是一种即使在复杂混合物和组织切片中也能明确鉴定PE为负离子的简单方法，并且无需在MS检测之前分离各个脂质类别。

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