Matrix-assisted laser desorption/ionization (MALDI) is an important method to analyze such biomolecules as proteins. In particular, MALDI using an infrared laser (IR-MALDI) is expected to measure various samples such as sugar chains, lipids, and cells because a molecular vibration can be directly excited by IR laser. We developed an IR-MALDI time-of-flight mass spectrometer (TOFMS) using a tunable IR laser (Difference Frequency Generation laser: DFG laser) that can adjust wavelength from 5.5 to 10 μm. The mass-to-charge spectra of insulin with a succinic acid matrix can be taken at a wavelength of 5.8 μm, which differs from the infrared absorption of succinic acid. With a urea or sinapic acid matrix, insulin spectra are detected by irradiating the DFG laser with the wavelength shifted from the absorption of these matrices.
