title: Correlation between Sweet Spots of Glycopeptides and Polymorphism of the Matrix Crystal in MALDI Samples.
abstract: A standard dried-droplet preparation using 2,5-dihydroxybenzoic acid (2,5-DHBA) as the matrix results in a large variation in signal intensity and poor shot-to-shot reproducibility in matrix-assisted laser desorption/ionization (MALDI). We expected that the differences can be attributed to the nature of the crystal structures in the region of the "sweet spot" within the MALDI samples. 2,5-DHBA crystals with and without analytes on a target plate obtained by means of a dried-droplet preparation contain two polymorphs, which can be distinguished by Raman spectra. In comparing the Raman image with the MS image, a clear correlation between the signal distribution of glycopeptides and hydrophilic peptides and the specific crystal form of 2,5-DHBA could be made. The ionization of hydrophobic peptides appears to proceed in both types of polymorphic crystals. In addition, the derivatization of glycopeptides with a pyrene group enabled us to detect glycopeptides regardless the crystal form. As the result, the number of sweet spots increased and MS spectra with a high signal intensity were obtained. The results suggest that the introduction of a hydrophobic/aromatic moiety to glycopeptides results in a more successful MALDI analysis due to the effective incorporation of the analyte into matrix crystals.
authors.affiliation: Laboratory of Glycobiology, The Noguchi Institute.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nishikaze
authors.affiliation: Laboratory of Glycobiology, The Noguchi Institute.
authors.forename: Hisako
authors.initials: H
authors.lastname: Okumura
authors.affiliation: Laboratory of Glycobiology, The Noguchi Institute.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Jinmei
authors.affiliation: Laboratory of Glycobiology, The Noguchi Institute.
authors.forename: Junko
authors.initials: J
authors.lastname: Amano
keywords: MALDI; matrix crystal; polymorphism; sweet spot