Collision-induced dissociation mass spectra of anions derived from α-hydroxy carboxylic acids (AHAs) show a diagnostic peak at m/z 45. Product ion spectra recorded from this m/z 45 ion confirm that it represents the hydroxycarbonyl anion ( ), and not the formate anion ( ) as sometimes described in the literature. For example, the formate anion is not only defiant to further fragmentation but is also unreactive toward CO2. In contrast, the hydroxycarbonyl anion easily fragments to produce a peak at m/z 17 for the hydroxyl anion, and also readily reacts with CO2 to produce a peak at m/z 61 for the bicarbonate anion. The hydrogen atom in the hydroxycarbonyl anion and that in the formate anion are not mobile within the skeletal framework of the ions, since the two ions did not manifest any interconversion under the conditions and time scales of our mass spectrometric experiments. The other significant product ion peak in the spectra of deprotonated AHAs represents a 46-Da loss. MS/MS data from appropriately deuteriated compounds confirmed that one hydrogen atom from the C-2 position, and the other from the hydroxy group are specifically removed for this loss of elements of formic acid. Moreover, the two oxygen atoms eliminated for the HCOOH loss originate exclusively from the carboxylate group. Copyright © 2008 John Wiley & Sons, Ltd.
α-羟基
羧酸(AHA)阴离子的碰撞诱导解离质谱显示出 m/z 45 的诊断峰。从这个 m/z 45 离子记录的产物离子光谱可以确认,它代表的是羟基羰基阴离子( ),而不是文献中有时描述的
甲酸根阴离子( )。例如,
甲酸阴离子不仅不能进一步碎裂,而且对
CO2 也没有反应。相反,羟羰基阴离子很容易碎裂,在 m/z 17 处产生羟羰基阴离子峰,也很容易与 反应,在 m/z 61 处产生
碳酸氢盐阴离子峰。羟基羰基阴离子中的
氢原子和
甲酸根阴离子中的
氢原子在离子的骨架框架内不具有流动性,因为在我们的质谱实验条件和时间尺度下,这两种离子没有表现出任何相互转化。在去质子化 AHA 的光谱中,另一个重要的产物离子峰代表 46-Da 的损失。来自适当去质子化化合物的 MS/MS 数据证实,C-2 位置上的一个
氢原子和羟基上的另一个
氢原子在
甲酸元素损失时被特别移除。此外,HCOOH 损失所消除的两个
氧原子完全来自
羧酸基团。Copyright © 2008 John Wiley & Sons, Ltd. All Rights Reserved.