Asakawa Daiki, Saikusa Kazumi
Research Institute for Measurement and Analytical Instrumentation, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
Research Institute for Material and Chemical Measurement, National Institute of Advanced Industrial Science and Technology (AIST), National Metrology Institute of Japan (NMIJ), Tsukuba Central 3, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan.
J Am Soc Mass Spectrom. 2022 Aug 3;33(8):1548-1554. doi: 10.1021/jasms.2c00116. Epub 2022 Jul 19.
We propose the use of substituted benzyl ammonium species as thermometer ions to characterize the internal energy distribution of the ions produced by electrospray ionization (ESI). Crucially, we found that the activation of the benzyl ammonium species preferentially provided a benzyl cation via N-Cα bond cleavage. In addition, calculations at the CCSD(T)/cc-PVTZ//M06-2X-D3/6-311++G(d,p) level of theory revealed that the threshold energies of fragmentation of the tested model ions ranged from 86 to 192 kJ mol, significantly lower than those of conventional 4-substituted benzylpyridinium thermometer ions. Thus, the substituted benzyl ammoniums are suitable for the characterization of the ESI process under typical experimental conditions. Further, the internal energies of the ions were found to depend on the radiofrequency voltage of the ion funnel, which is used to increase the transport efficiency of the ions from atmospheric to vacuum conditions. Our reported method will aid the determination of the optimum ion-funnel radiofrequency voltage for the analysis of small molecules such as metabolites. Furthermore, benzyl ammoniums are commercially available, which will facilitate the routine and widespread measurement of the internal energy distributions of ions.
我们建议使用取代苄基铵类作为温度计离子，以表征电喷雾电离（ESI）产生的离子的内能分布。至关重要的是，我们发现苄基铵类的活化优先通过N-Cα键裂解提供苄基阳离子。此外，在CCSD(T)/cc-PVTZ//M06-2X-D3/6-311++G(d,p)理论水平上的计算表明，测试的模型离子的碎片化阈值能量范围为86至192 kJ/mol，显著低于传统的4-取代苄基吡啶鎓温度计离子。因此，取代苄基铵类适用于在典型实验条件下表征ESI过程。此外，发现离子的内能取决于离子漏斗的射频电压，离子漏斗用于提高离子从大气条件到真空条件的传输效率。我们报道的方法将有助于确定用于分析代谢物等小分子的最佳离子漏斗射频电压。此外，苄基铵类可商购获得，这将便于常规且广泛地测量离子的内能分布。
