Oligosaccharides demonstrate many bioactivities with applications in the pharmaceutical, cosmetic, and food industries. They also serve as biomarkers for various diseases including cancer and glycogen storage disorders. These make the structural characterization of oligosaccharides very important. Unfortunately, the structural diversity found in saccharides make their characterization challenging, necessitating the development of sophisticated instrumentation to enable isomer differentiation. Herein, we report the ability of halide (Cl⁻ and Br⁻) adducts to enable direct differentiation of oligosaccharide isomers using conventional collision-induced dissociation (CID) tandem MS (MS/MS). The halide adducts were generated by direct infusion nano-electrospray ionization (nESI). For the first time, this traditional nESI CID MS/MS platform was used to differentiate stereoisomers of trisaccharides (cellotriose β(1 → 4) and maltotriose α(1 → 4), tetrasaccharides (cellotetraose and maltotetraose), and pentasaccharides (cellopentaose and maltopentaose)). In addition, the MS/MS of halide adducts enabled the differentiation of positional, structural, and linkage isomers from a total of 14 oligosaccharides. The isomer differentiation was realized by the generation of distinct diagnostic fragment ions in CID. We also performed principal component analysis using the entire range of MS/MS fragment ion profiles and found that negative-ion mode halide adduction provided more effective isomer differentiation compared with positive-ion mode sodium adduction. Finally, we demonstrated complex mixture analysis by spiking all 14 oligosaccharides into raw urine, of which we successfully distinguished species based on molecular weight (first dimension) and CID MS/MS fragmentation patterns as the second dimension separation. This work effectively showcases the potential to use direct infusion nESI-MS/MS to characterize synthetic oligosaccharide isomers in unpurified reaction mixture as well as from biofluids for diagnostic purposes.

中文翻译：

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通过直接输注多维质谱法区分寡糖异构体


低聚糖在制药、化妆品和食品工业中表现出许多生物活性。它们还可以作为各种疾病的生物标志物，包括癌症和糖原贮积症。这使得低聚糖的结构表征非常重要。不幸的是，糖类中的结构多样性使其表征具有挑战性，因此需要开发复杂的仪器来实现异构体分化。在此，我们报道了卤化物（Cl^-和Br^-）加合物使用常规碰撞诱导解离 （CID） 串联 MS （MS/MS） 实现寡糖异构体直接分化的能力。卤化物加合物是通过直接注入纳米电喷雾电离 （nESI） 产生的。这种传统的 nESI CID MS/MS 平台首次用于区分三糖（纤维三糖 β（1 → 4）和麦芽三糖α（1 → 4）、四糖（纤维四糖和麦芽四糖）和五糖（细胞戊糖和麦芽戊糖）的立体异构体。此外，卤化物加合物的 MS/MS 能够从总共 14 种寡糖中区分位置、结构和键合异构体。异构体分化是通过在 CID 中产生不同的诊断碎片离子来实现的。我们还使用整个 MS/MS 碎片离子曲线范围进行了主成分分析，发现与正离子模式钠加收相比，负离子模式卤化物加收提供了更有效的异构体区分。 最后，我们通过将所有 14 种低聚糖加标到生尿液中来演示复杂的混合物分析，其中我们根据分子量（第一维）和 CID MS/MS 碎裂模式成功区分了物种作为第二维分离。这项工作有效地展示了使用直接输注 nESI-MS/MS 来表征未纯化反应混合物中合成寡糖异构体以及用于诊断目的的生物流体的潜力。