Isomer identification by metastable decay rates of laser-produced ions.
Isomer identification by metastable decay rates of laser-produced ions.
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通过激光产生的离子的亚稳态衰变率识别异构体。
DOI：
10.1021/ac00170a020
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发表时间：
1988
影响因子：
7.4
通讯作者：
Johnston,MV
中科院分区：
文献类型：
--
作者：
Kinsel,GR;Johnston,MV
提出了一种新的异构体鉴定方法。线性飞行时间质谱仪中共振增强多光子电离产生的亚稳定离子。根据o-、m-和p-氯蓝素质谱中亚稳尾的形状和强度，计算了m/z 91、92、100和102形成的母离子衰变率。这些值对于每种化合物都是不同的。与相对离子丰度的简单测量相比，衰变率测量提供了额外的结构和机制信息，包括各自的母离子在破碎之前是否重新排列成共同的形式。讨论了该技术的潜在分析应用。用质谱法区分有机分子的不同异构体结构是很困难的。邻苯、间苯和对取代苯的70 ev电子冲击（El）质谱在许多情况下几乎相同。由于不同的异构体结构可能具有广泛不同的毒理学性质和环境影响，因此了解确切的异构体结构非常重要。各种质谱技术已经发展到区分分子的不同同分异构体。在El质谱中，片段离子丰度(1)或释放到片段离子的动能（2-4）的差异可用于识别特定的异构体。每个都可以通过将光解（5-7）或碰撞诱导解离（8,9）步骤纳入程序来增强。这些测量对前体离子的内能非常敏感。如果不同异构体破碎动力学的微小差异被产生的母离子集合的广泛内部能量分布所掩盖（10,11），或者如果不同构型的母离子在破碎之前异构成一个或一组共同的结构，那么这两种方法都将失败。我们在这里提出的证据表明，共振增强多光子电离（REMPI）结合线性飞行时间质谱仪（TOF-MS）也可以用于异构体鉴定。与前面提到的技术相比，REMPI创造了一个更窄的母离子内能分布，可以提供所需的灵敏度来检测不同异构体的碎片能量的微小变化。最初，人们认为REMPI质谱不能用于同分异构体的鉴定，因为特定的同分异构体对具有相同的REMPI质谱（12,13）。然而，我们小组最近的工作表明，C7H80和c8h100的构型异构体确实可以根据它们的REMPI质谱来区分（14）。这些化合物也可以用70 ev的El质谱和子离子碰撞诱导解离谱来区分。在另一份报告中，发现碘丁烷的三个同分异构体的REMPI质谱是不可区分的，即使它们的70-eV El质谱是相同的（15）。在这种情况下，差异
A new method for Isomer Identification is presented. Meta-stable Ionsare produced by resonance enhanced multiphoton ionization In a linear tlme-of-fllght mass spectrometer. From the shapes and Intensities of metastable tails in the mass spectra of o-, m-, and p-chloroanlllne, parent Ion decay rates for formation of m/z 91, 92, 100, and 102 are calculated. These values are different for each compound. In contrast to simple measurements of relative Ion abundances, decay rate measurements provide additional structural and mechanistic Information including whether or not the respective parent ions are rearranging to a common form prior to fragmentation. Potential analytical applications of this technique are discussed.Distinguishing among different isomeric configurations of an organic molecule by mass spectrometry can be difficult. The 70-eV electron impact (El) mass spectra of ortho-, meta-, and para-substituted benzenes are in many cases virtually identical. Knowledge of the exact isomeric configuration can be of great importance since different isomeric configurations may have widely varying toxicological properties and environmental impacts. Various mass spectrometric techniques have been developed todistinguish among the different iso-mers of a molecule. In El mass spectra, differencesin either fragment ion abundances (1) or the kinetic energy released to the fragment ion (2-4) can be used to identify a particular isomer. Each can be augmented by incorporating photodissociation (5-7) or collision induced dissociation (8, 9) steps into theprocedure. These measurements can be extremely sensitive to the internal energy of the precursor ion. Both of these approaches will fail if small differences in the frag-mentation dynamics of different isomers are masked by a broad internal energy distribution of the ensemble of parent ions produced (10, 11) or if parent ions of different configurations isomerize to a common structure or set of structures prior to fragmentation. We present evidencehere that res-onance enhanced multiphoton ionization (REMPI) combined with a linear time-of-flight mass spectrometer (TOF-MS) can also be used for isomer identification. In contrast to the previously mentioned techniques, REMPI creates a much narrower distribution of parent ion internal energies that can provide the required sensitivity to detect small changes in the fragmentation energetics of different isomers. Originally, it was believed that REMPI mass spectra could not be used for isomer identification since specific isomer pairs exhibited identical REMPI mass spectra (12, 13). Recent work by our group, however, has shown that C7H80 and C8H10O configurational isomers can indeed be distinguished on the basis of their REMPI mass spectra (14). These compounds can also be distinguished by 70-eV El mass spectra and by daughter ion collision induced dissociation spectra. In another report, three isomers of iodobutane were found to give dis-tinguishable REMPI mass spectra even though their 70-eV El mass spectra are identical (15). In this case, differences