Although liquid chromatography-tandem mass spectrometry (LC-MS/MS) equipped with electrospray ionization (ESI) is widely employed for metabolite analysis, substituted phenethylamines commonly undergo fragmentation during ESI in-source collision-induced dissociation (CID). Unexpected fragmentation hampers not only unambiguous identification but also accurate metabolite quantification. ESI in-source CID induces N-Cα bond dissociation in substituted phenethylamines lacking a β-hydroxy group to produce fragment ions with a spiro[2.5]octadienylium motif. In contrast, phenethylamines with a β-hydroxy group generate substituted 2-phenylaziridium through ESI in-source CID-induced H2O loss. The fragment ion yield produced by ESI in-source CID can be estimated by the dissociation rate constant and internal energy of the analyte ion, determined by employing density functional theory calculations and the survival yield method using a thermometer ion, respectively. Fragmentation is strongly enhanced by the presence of an β-hydroxy group, whereas N-methylation suppresses fragmentation. In particular, octopamine and noradrenaline, which contain an β-hydroxy and primary amine groups, produce more intense fragment ion signals than protonated molecules. Regarding the quantitative analysis of phenethylamines present in the mouse brain, the noradrenaline fragment ion used as the precursor in multiple reaction monitoring (MRM) provided a higher signal-to-noise ratio in the resulting spectra than protonated noradrenaline. The present method allows for the quantitative analysis of substituted phenethylamines with high sensitivity.

中文翻译：

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电喷雾电离质谱诱导的取代苯乙胺断裂的研究及其在生物样品中神经递质高灵敏分析中的应用。


尽管配备电喷雾电离 (ESI) 的液相色谱-串联质谱 (LC-MS/MS) 广泛用于代谢物分析，但取代的苯乙胺通常在 ESI 源内碰撞诱导解离 (CID) 过程中发生碎裂。意外的碎片不仅妨碍明确的识别，而且妨碍准确的代谢物定量。 ESI 源 CID 诱导缺乏 β-羟基的取代苯乙胺中的 N-Cα 键解离，产生带有螺[2.5]辛二烯基基序的碎片离子。相比之下，带有 β-羟基的苯乙胺通过 ESI 源内 CID 诱导的 H2O 损失生成取代的 2-苯基氮丙啶。 ESI 源内 CID 产生的碎片离子产率可以通过分析物离子的解离速率常数和内能进行估计，分别通过密度泛函理论计算和使用温度计离子的存活产率方法确定。 β-羟基的存在强烈增强了断裂，而 N-甲基化则抑制了断裂。特别是，含有β-羟基和伯胺基的章鱼胺和去甲肾上腺素会产生比质子化分子更强烈的碎片离子信号。关于小鼠大脑中苯乙胺的定量分析，在多反应监测 (MRM) 中用作前体的去甲肾上腺素碎片离子在所得光谱中提供了比质子化去甲肾上腺素更高的信噪比。本方法允许以高灵敏度定量分析取代的苯乙胺。