Distinction among isomeric unsaturated fatty acids as lithiated adducts by electrospray ionization mass spectrometry using low energy collisionally activated dissociation on a triple stage quadrupole instrument
Distinction among isomeric unsaturated fatty acids as lithiated adducts by electrospray ionization mass spectrometry using low energy collisionally activated dissociation on a triple stage quadrupole instrument
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DOI：
10.1016/s1044-0305(99)00041-0
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发表时间：
1999-07-01
影响因子：
3.2
通讯作者：
Turk, J
中科院分区：
文献类型：
--
作者：
Hsu, FF;Turk, J
本文介绍了在三级四极杆质谱仪上用低能碰撞活化解离（CAD）电喷雾电离质谱法获得的不饱和脂肪酸硫代加合离子的串联质谱特征。这些光谱区分异构的不饱和脂肪酸，并允许分配双键的位置。信息碎片离子反映了远离二硫代羧酸盐部分上电荷位点的键的裂解。光谱中含有自由基阳离子，反映了脂肪酸链中第一个和第二个碳原子之间以及第二个和第三个碳原子之间的键断裂。这些离子之后是一个闭壳层离子系列，其中成员由14 m/z单位分开，反映了第三和第四个碳原子之间以及随后的相邻碳原子对之间的键断裂。该离子系列终止于反映碳-碳单键乙烯基裂解为第一个碳-碳双键的成员。反映双键远端键裂解的离子很少在单不饱和脂肪酸中观察到，并且在发生时并不丰富。对于含有被单个亚甲基分开的双键的多不饱和脂肪酸，反映双键之间的碳-碳单键裂解的离子是丰富的，但反映最终双键远端裂解的离子不是。在这些光谱中观察到的双键之间的裂解可以合理化的一个计划，涉及一个六元过渡态和随后的：重排的双烯丙基氢原子，以产生一个末端不饱和的带电片段和消除的中性烯烃。β-羟基-烯烃部分在蓖麻油酸中的位置可以通过类似的方法证明。这些观测为那些拥有串联四极杆仪器但没有的实验室提供了机会。拥有具有高能CAD功能的仪器，可通过质谱法在不饱和游离脂肪酸中分配双键位置，无需衍生化。(C)1999年美国质谱学会。
Features of tandem mass spectra of dilithiated adduct ions of unsaturated fatty acids obtained by electrospray ionization mass spectrometry with low-energy collisionally activated dissociation (CAD) on a triple stage quadrupole instrument are described. These spectra distinguish among isomeric unsaturated fatty acids and permit assignment of double-bond location. Informative fragment ions reflect cleavage of bonds remote from the charge site on the dilithiated carboxylate moiety. The spectra contain radical cations reflecting cleavage of bonds between the first and second and between the second and third carbon atoms in the fatty acid chain. These ions are followed by a closed-shell ion series with members separated by 14 m/z units that reflect cleavage of bonds between the third and fourth and then between subsequent adjacent pairs of carbon atoms. This ion series terminates at the member reflecting cleavage of the carbon-carbon single bond vinylic to the first carbon-carbon double bond. Ions reflecting cleavages of bonds distal to the double bond are rarely observed for monounsaturated fatty acids and are not abundant when they occur. For polyunsaturated fatty acids that contain double bonds separated by a single methylene group, ions reflecting cleavage of carbon-carbon single bonds between double bonds are abundant, but ions reflecting cleavages distal to the final double bond are not. Cleavages between double bonds observed in these spectra can be rationalized by a scheme involving a six-membered transition state and subsequent: rearrangement of a bis-allylic hydrogen atom to yield a terminally unsaturated charge-carrying fragment and elimination of a neutral alkene. The location of the beta-hydroxy-alkene moiety in ricinoleic acid can be demonstrated by similar methods. These observations offer the opportunity for laboratories that have tandem quadrupole instruments but do not. have instruments with high energy CAD capabilities to assign double bond location in unsaturated free fatty acids by mass spectrometric methods without derivatization. (C) 1999 American Society for Mass Spectrometry.