School of Chemistry, University of Wollongong, Wollongong, NSW, Australia.
J Am Soc Mass Spectrom. 2013 Feb;24(2):286-96. doi: 10.1007/s13361-012-0521-9. Epub 2013 Jan 5.
Ozone-induced dissociation (OzID) is an alternative ion activation method that relies on the gas phase ion-molecule reaction between a mass-selected target ion and ozone in an ion trap mass spectrometer. Herein, we evaluated the performance of OzID for both the structural elucidation and selective detection of conjugated carbon-carbon double bond motifs within lipids. The relative reactivity trends for M + X ions (where X = Li, Na, K) formed via electrospray ionization (ESI) of conjugated versus nonconjugated fatty acid methyl esters (FAMEs) were examined using two different OzID-enabled linear ion-trap mass spectrometers. Compared with nonconjugated analogues, FAMEs derived from conjugated linoleic acids were found to react up to 200 times faster and to yield characteristic radical cations. The significantly enhanced reactivity of conjugated isomers means that OzID product ions can be observed without invoking a reaction delay in the experimental sequence (i.e., trapping of ions in the presence of ozone is not required). This possibility has been exploited to undertake neutral-loss scans on a triple quadrupole mass spectrometer targeting characteristic OzID transitions. Such analyses reveal the presence of conjugated double bonds in lipids extracted from selected foodstuffs. Finally, by benchmarking of the absolute ozone concentration inside the ion trap, second order rate constants for the gas phase reactions between unsaturated organic ions and ozone were obtained. These results demonstrate a significant influence of the adducting metal on reaction rate constants in the fashion Li > Na > K.
臭氧诱导解离（OzID）是一种替代的离子活化方法，它依赖于在离子阱质谱仪中，质量选择的靶离子与臭氧之间的气相离子-分子反应。在此，我们评估了 OzID 在脂质中共轭碳-碳双键结构的阐明和选择性检测方面的性能。通过使用两种不同的OzID 线性离子阱质谱仪，研究了电喷雾电离（ESI）形成的[M + X] +（其中 X = Li、Na、K）离子的相对反应性趋势，这些离子来自共轭和非共轭脂肪酸甲酯（FAME）。与非共轭类似物相比，共轭亚油酸衍生的 FAME 被发现反应速度快 200 倍，并且产生特征自由基阳离子。共轭异构体的显著增强的反应性意味着可以观察到 OzID 产物离子，而无需在实验序列中引入反应延迟（即，不需要在存在臭氧的情况下捕获离子）。这一可能性已被用于针对特征 OzID 跃迁对三重四极杆质谱仪进行中性丢失扫描。这样的分析揭示了从选定食品中提取的脂质中存在共轭双键。最后，通过对离子阱内臭氧的绝对浓度进行基准测试，获得了不饱和有机离子与臭氧之间气相反应的二级速率常数。这些结果表明，加合物金属对反应速率常数的影响显著，Li > Na > K。
