Small peptides, such as dipeptides, have attracted attention in many research fields because of their important biological functions and potential roles as disease biomarkers. However, the identification of many of them by implementation of liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS/MS) is a challenging task. This is because many dipeptides display limited mass spectral information in LC–ESI–MS/MS analyses, which leads to unavoidable ambiguity in determinations of their structures. In this study, two useful analytical techniques were developed for the structural elucidation of 10 representative dipeptides exhibiting a dominant/single product ion in the ESI–MS/MS spectra of the protonated molecules [M + H]⁺. Structural elucidation was obtained instantaneously through LC–ESI–MS/MS fragmentation of the accompanying sodium adducts [M + Na]⁺ or alternatively by “in-vial” chemical derivatization with isobutyl chloroformate. The sodium adducts and the resulting carbamate derivatives altered the charge distribution occurring during ESI–MS/MS fragmentation, enabling detailed structural elucidation and unambiguous identification of such dipeptides at ng/ml levels. These quick, simple, and easy techniques can be implemented to identify various dipeptides or confirm their identities without the need for complex sample handling.

中文翻译：

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液相色谱-电喷雾电离-串联质谱法对显示有限质谱信息的二肽的结构解析

小肽，如二肽，因其重要的生物学功能和作为疾病生物标志物的潜在作用而在许多研究领域受到关注。然而，通过实施液相色谱-电喷雾电离-串联质谱 (LC-ESI-MS/MS) 鉴定其中的许多是一项具有挑战性的任务。这是因为许多二肽在 LC-ESI-MS/MS 分析中显示有限的质谱信息，这导致在确定其结构时不可避免地存在歧义。在这项研究中，开发了两种有用的分析技术，用于对质子化分子 [M + H] ⁺. ^{通过伴随的钠加合物 [M + Na] +}的 LC-ESI-MS/MS 碎裂，或者通过氯甲酸异丁酯的“瓶内”化学衍生化，立即获得结构解析。钠加合物和由此产生的氨基甲酸酯衍生物改变了 ESI-MS/MS 碎裂过程中发生的电荷分布，从而能够在 ng/ml 水平上对此类二肽进行详细的结构解析和明确鉴定。这些快速、简单和容易的技术可用于识别各种二肽或确认其身份，而无需复杂的样品处理。