Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
Analyst. 2016 Sep 21;141(18):5274-80. doi: 10.1039/c6an00577b. Epub 2016 Jun 21.
Ionization efficiency in mass spectrometry was examined for three types of molecules under different ionization schemes, i.e., resonant/nonresonant and two-photon/three-photon ionization, using an ultraviolet (UV) femtosecond laser at different wavelengths, pulse energies, and pulse widths. The efficiency of nonresonant ionization could be improved substantially by decreasing the laser pulse width. The effect of resonance was minimal when an ultrashort optical pulse of less than 100 fs was employed for ionization in the UV region. Three-photon ionization was less efficient than two-photon ionization, but the difference was not significant at shorter pulse widths in the femtosecond region. Although the excess energy can be decreased by optimizing the laser wavelength in the case of nonresonant ionization, fragmentation was not suppressed in the cases studied here. However, fragmentation was drastically suppressed when the laser pulse width was decreased. Thus, this approach of using an ultrashort optical pulse would provide a new tool for soft ionization and then for more reliable identification of an analyte.
我们在不同的电离方案（即共振/非共振和双光子/三光子电离）下，使用不同波长、脉冲能量和脉冲宽度的紫外（UV）飞秒激光，研究了三种分子的电离效率。通过降低激光脉冲宽度，可以显著提高非共振电离的效率。当在 UV 区域中使用小于 100 fs 的超短光脉冲进行电离时，共振的影响最小。三光子电离的效率低于双光子电离，但在飞秒区域中较短的脉冲宽度下，差异并不显著。虽然在非共振电离的情况下可以通过优化激光波长来降低多余能量，但在本研究中没有抑制碎片。然而，当激光脉冲宽度减小时，碎片会被显著抑制。因此，这种使用超短光脉冲的方法将为软电离提供一种新的工具，从而更可靠地识别分析物。
