Secondary ion mass spectrometry (SIMS) offers advantages over both liquid extraction mass spectrometry and matrix assisted laser desorption mass spectrometry in that it provides the direct in situ analysis of molecules and has the potential to preserve the 3D location of an analyte in a sample. Polysaccharides are recognized as challenging analytes in the mass spectrometry of liquids and are also difficult to identify and assign using SIMS. Psl is an exopolysaccharide produced by Pseudomonas aeruginosa, which plays a key role in biofilm formation and maturation. In this Letter, we describe the use of the OrbiTrap analyzer with SIMS (3D OrbiSIMS) for the label-free mass spectrometry of Psl, taking advantage of its high mass resolving power for accurate secondary ion assignment. We study a P. aeruginosa biofilm and compare it with purified Psl to enable the assignment of secondary ions specific to the Psl structure. This resulted in the identification of 17 peaks that could confidently be ascribed to Psl fragments within the biofilm matrix. The complementary approach of the following neutral loss sequences is also shown to identify multiple oligosaccharide fragments without the requirement of a biological reference sample.

中文翻译：

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使用 3D OrbiSIMS 鉴定生物膜中的铜绿假单胞菌胞外多糖 Psl。

二次离子质谱 (SIMS) 比液体萃取质谱和基质辅助激光解吸质谱具有优势，因为它可以直接对分子进行原位分析，并且有可能保留样品中分析物的 3D 位置。多糖被认为是液体质谱分析中具有挑战性的分析物，并且也很难使用 SIMS 进行识别和分配。Psl是由铜绿假单胞菌产生的胞外多糖，在生物膜的形成和成熟中起着关键作用。在这封信中，我们描述了使用带有 SIMS (3D OrbiSIMS) 的 OrbiTrap 分析仪进行 Psl 的无标记质谱分析，利用其高质量分辨能力进行精确的二次离子分配。我们研究了铜绿假单胞菌生物膜，并将其与纯化的 Psl 进行比较，以便能够分配特定于 Psl 结构的二次离子。这导致鉴定出 17 个峰，这些峰可以确信地归因于生物膜基质内的 Psl 片段。还显示以下中性丢失序列的互补方法可以识别多个寡糖片段，而无需生物参考样品。