In Search of Methodology Determineng Kinetic Isotope Effect on Organic Fundamental Reactions

为了寻找一种方法来确定动力学同位素对普通有机化学实验室基本有机反应的影响，我们探索了用双聚焦高分辨率质谱仪进行全分子质谱分析的可能性。为此，通常选择四极质谱仪，因为它可以快速重复扫描质量峰。在日本的研究机构中，与高分辨率质谱仪相比，四极杆仪器的普及程度要低得多，而且这种稀缺的可用性似乎限制了这种可能有用的同位素效应测量手段的应用。然而，最近的创新允许用高分辨率仪器快速和重复扫描质量峰，从而使我们更容易参与同位素效应研究。JEOL JMS-DX302质谱仪被用于此目的，并且工作得很好。用氯化苄、邻二氯苯和对二氯苯测定了分子离子峰的同位素峰比。在累积2万次扫描后，以峰值面积测量峰值强度时，精度可达到1 ~ 1万次。但是，要想取得满意的全分子质谱分析结果，还需要进行一些保留和进一步的改进。例如，改进数据累加器的动态范围将保证更高的精度，提供更好的尾部检测管理。

In search of a methodology to determine the kinetic isotope effect on fundamental organic reactions in an ordinary organic chemistry laboratory, we pursued the possibility of conducting whole molecule mass spectrometry with a double-focusing high resolution mass spectrometer. For this purpose, a quadrupole mass spectrometer is generally an instrument of choice because it allows a rapid and repeated scanning of mass peaks.In Japanese institutions, quadrupole instrument is far less popular compared to high resolution mass spectrometers and such a scarce availability seem to limit the application of this potentially useful means of isotope effect measurements.However, recent innovations allow rapid and repeated scanning of mass peaks with a high resolution instrument, thus allowing us to be involved in an isotope effect study more easily. A JEOL JMS-DX302 mass spectrometer was utilized for this purpose and worked beautifully. Isotope peak ratio for molecular ion peaks are determined with benzyl chloride, o- and p-dichlorobenzene. On accumulating 20,000 scans, the accuracy could reach as good as 1 to 10,000 when the peak intensities are measured by a peak area. Some reservations and further improvements should be made, however, to do satisfactory whole molecule mass spectrometry. For example, an improved dynamic range of data accumulator would promise a higher accuracy, provided a better tail detection is managed.