Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei, 10617, Taiwan.
Department of Chemistry, Wayne State University, Detroit, MI, 48202, USA.
J Am Soc Mass Spectrom. 2019 Aug;30(8):1455-1463. doi: 10.1007/s13361-019-02208-4. Epub 2019 Apr 16.
Since its introduction, matrix-assisted laser desorption/ionization (MALDI) has been widely used for the mass analysis of biomolecules. The "soft ionization" of MALDI enables accurate mass determination of intact biomolecules. However, the ionization and desorption processes of MALDI are not adequately soft as many labile biomolecules, such as glycoconjugates containing sialic acid or the sulfate functional group, easily dissociate into fragments and sometimes, no intact molecules are observed. In this study, we compared the conventional matrix of MALDI, namely 2,5-dihydroxybenzoic acid, to various soft matrices of MALDI-specifically, 5-methoxysalicylic acid, diamond nanoparticle trilayers, HgTe nanostructures, ionic liquid, and droplets of frozen solutions-by using three labile glycoconjugates as analytes: gangliosides, heparin, and pullulan. We demonstrated that droplets of frozen solution are the softest matrices for gangliosides and heparin. In particular, droplets of frozen solution do not generate fragments for gangliosides and can be used to determine the relative abundance of various gangliosides, whereas ionic liquid 2,5-dihydroxybenzoic acid butylamine is the most suitable matrix for pullulan mass analysis. Graphical Abstract.
自问世以来，基质辅助激光解吸/电离（MALDI）已被广泛应用于生物分子的质谱分析。MALDI 的“软电离”可实现完整生物分子的精确质量测定。然而，MALDI 的离子化和解析过程并不够柔和，许多不稳定的生物分子，如含有唾液酸或硫酸基团的糖缀合物，容易分解成碎片，有时甚至观察不到完整的分子。在这项研究中，我们将 MALDI 的常规基质，即 2,5-二羟基苯甲酸，与各种 MALDI 专用软基质进行了比较，具体包括 5-甲氧基水杨酸、金刚石纳米薄膜三层、HgTe 纳米结构、离子液体和冷冻溶液液滴，使用三种不稳定的糖缀合物作为分析物：神经节苷脂、肝素和普鲁兰多糖。结果表明，冷冻溶液液滴是神经节苷脂和肝素的最软基质。特别是，冷冻溶液液滴不会产生神经节苷脂的碎片，可用于测定各种神经节苷脂的相对丰度，而离子液体 2,5-二羟基苯甲酸丁胺则是普鲁兰多糖质谱分析最适合的基质。
