2008 年 56 巻 5 号 p. 235-240
Infrared matrix-assisted laser desorption/ionization (IR-MALDI) using an infrared laser is promising, because most biomolecules have a specific absorption in the infrared range. IR-MALDI is expected to provide the following advantages: (1) use of various matrices; (2) use of biomolecules such as water and lipids as the matrix; and (3) super-soft ionization, i.e., high-molecular-weight protein analysis without fragmentation. However, IR-MALDI is not widely used because of its low sensitivity, complexity, high cost, and low-compatibility with commercial MALDI time-of-flight mass spectrometers. We evaluated the wavelength dependence of ionization in IR-MALDI to clarify the ionization mechanism. The molecular mass of angiotensin II was obtained at a wavelength between 5.8 and 6.2 μm, which corresponds to the >C=O stretching vibration mode. In IR-MALDI, we believe that the strong molecular bond attracts an electron from a neighboring hydrogen atom, possibly protonating it.