Development of a multi-frequency laser for use in MALDI-TOFMS

The application of a multi-frequency laser source for the use in matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) is described. An elliptically polarized beam of a Nd:YAG laser emitting at 355 nm (200 mJ) is focused into a Raman shifter, filled with high pressure hydrogen. As a result, numerous Raman lasers (including vibrational and rotational Raman emissions for hydrogen; 4155 and 587 cm^-1 shifts, respectively) were generated with a total power of ∼100 mJ. Using this multi-frequency laser as an ionization source, methionine enkephalin (MW 573.7), angiotensin I (MW 1296.5) and oxidized insulin chain B (MW 3495.9) were examined, as model compounds using α-cyano-4-hydroxycinnamic acid (CHCA), sinapinic acid (SA) and activated charcoal as the matrix, respectively. As a result, the S/N ratios were improved when the multi-frequency laser was used, compared to the single light source of the Nd:YAG laser (355 nm), irrespective of the type of matrix used. This is because the multi-frequency laser provides multi-line for absorption, where the traditional N₂ laser only provides single wavelength (at 337 nm) for absorption.