Lorkiewicz Pawel, Cecilia Yappert M
Department of Chemistry, University of Louisville, Louisville, KY 40292, USA.
J Mass Spectrom. 2009 Jan;44(1):137-43. doi: 10.1002/jms.1483.
Fast and easy analysis of phospholipids (PLs) by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been well demonstrated. However, when using common organic matrices, such as 2,5-dihydroxybenzoic acid (DHB), the detection of most PL classes in positive-ion mode is difficult when PLs containing zwitterionic groups, such as phosphatidylcholines (PCs) and sphingomyelins (SMs) are present. To reduce this limitation, 2-(2-aminoethyloamino)-5-nitropyridine (AAN), a basic compound, was evaluated as an alternative matrix. Negative-ion spectra showed enhanced detection of phosphatidyl ethanolamines (PEs), phosphatidyl serines (PSs), phosphatidyl glycerols (PGs), and phosphatidyl inositols (PIs) in simple mixtures and in a crude methanolic soybean extract. The relative ionization efficiency (RIE) was highest for PIs and lowest for PGs, PSs, and PEs. Compared to DHB and para-nitroaniline, AAN resulted in greater sensitivity for the detection of PL classes in the negative mode. Indeed, the S/N ratio was nearly an order of magnitude higher than that reported for similar PI concentrations but with DHB. MALDI spots produced with AAN were homogeneous thus allowing automation and improved reproducibility. Positive-mode traces could also be acquired with AAN as the matrix, but with lower sensitivity than in the negative mode.
基质辅助激光解吸/电离质谱（MALDI-MS）对磷脂（PLs）进行快速简便的分析已得到充分证明。然而，当使用常见的有机基质，如2,5-二羟基苯甲酸（DHB）时，在存在含两性离子基团的磷脂（如磷脂酰胆碱（PCs）和鞘磷脂（SMs））的情况下，在正离子模式下检测大多数PL类别很困难。为了减少这一限制，对一种碱性化合物2-(2-氨基乙基氨基)-5-硝基吡啶（AAN）作为替代基质进行了评估。负离子光谱显示，在简单混合物和粗甲醇大豆提取物中，磷脂酰乙醇胺（PEs）、磷脂酰丝氨酸（PSs）、磷脂酰甘油（PGs）和磷脂酰肌醇（PIs）的检测得到了增强。相对电离效率（RIE）对PIs最高，对PGs、PSs和PEs最低。与DHB和对硝基苯胺相比，AAN在负离子模式下对PL类别的检测具有更高的灵敏度。事实上，信噪比几乎比报道的类似PI浓度但使用DHB时高出一个数量级。用AAN产生的MALDI斑点均匀，因此可以实现自动化并提高重现性。以AAN作为基质也可以获得正模式轨迹，但灵敏度低于负离子模式。
