Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan.
International Graduate Program of Molecular Science and Technology, National Taiwan University (NTU-MST), Taipei, Taiwan.
Rapid Commun Mass Spectrom. 2022 Sep 30;36(18):e9352. doi: 10.1002/rcm.9352.
Electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) are soft ionization techniques commonly used in mass spectrometry. Although in-source and post-source decays of MALDI have been investigated extensively, the analogous decays of ESI have received little attention. Previous studies regarding the analogous decays of ESI focus on the dissociation of multiply charged proteins and peptides. The decay of carbohydrates in ESI has not been investigated yet, and it may have interference in carbohydrate structural determination.
Commercial apparatus, including a high-performance liquid chromatography (HPLC), an ESI source, and a linear ion trap mass spectrometer, were used to investigate the fragmentation of several N-glycans during the ESI process.
About 0.2%-3% of neutral N-glycans and more than 50% of N-glycans consisting of a sialic acid are dissociated into small N-glycans by ESI in-source decay in typical ESI operating conditions. The efficiencies of most dissociation channels increase as the temperature of ion transfer capillary increases, indicating that part of the energy deposited into the precursor ions for cracking is from the heated capillary. The cracking patterns of ESI in-source decay are slightly different from those of gaseous phase collision-induced dissociation.
Large N-glycans are dissociated into small N-glycans in ESI in-source decay that may result in the interference of the structural identification of small N-glycans. Separation of large N-glycans from small N-glycans, for example, using HPLC, prior to ESI ionization is necessary to eliminate the interference. This is particularly important when N-glycans consist of sialic acid or large N-glycans have much higher concentration than that of small N-glycans in ESI solution.
ESI 和 MALDI 是常用于质谱的软电离技术。虽然 MALDI 的源内和源后衰变已经得到了广泛的研究，但 ESI 的类似衰变却很少受到关注。以前关于 ESI 类似衰变的研究主要集中在多电荷蛋白质和肽的解离上。ESI 中碳水化合物的衰变尚未得到研究，但它可能会干扰碳水化合物结构的确定。
使用商业仪器，包括高效液相色谱（HPLC）、ESI 源和线性离子阱质谱仪，研究了几种 N-聚糖在 ESI 过程中的碎裂。
在典型的 ESI 操作条件下，约 0.2%-3%的中性 N-聚糖和约 50%的含有唾液酸的 N-聚糖通过 ESI 源内衰变解离成小的 N-聚糖。大多数解离通道的效率随着离子转移毛细管温度的升高而增加，这表明部分用于裂解前体离子的能量来自加热的毛细管。ESI 源内衰变的裂解模式与气相碰撞诱导解离略有不同。
ESI 源内衰变会将大的 N-聚糖解离成小的 N-聚糖，这可能会干扰小的 N-聚糖的结构鉴定。在 ESI 离子化之前，例如使用 HPLC 将大的 N-聚糖从小的 N-聚糖中分离出来，以消除干扰，这在 ESI 溶液中 N-聚糖含有唾液酸或大的 N-聚糖的浓度比小的 N-聚糖高得多时尤为重要。
