Benefits of 2.94 micron infrared matrix-assisted laser desorption/ionization for analysis of labile molecules by Fourier transform mass spectrometry.

A 2.94 microm Er:YAG laser was used together with a commercial Fourier transform mass spectrometer to study labile biomolecules. The combination has shown superior performance over conventional 337 nm ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI) Fourier transform mass spectrometry (FTMS), especially for the analysis of peptides with post-translational modifications. With succinic acid as a matrix, the sensitivity of the single-shot analysis was increased by an order of magnitude to the low femtomole level, with significantly less fragmentation observed. Intact molecular ions of a range of O-glycosylated and sulfated peptides were detected. Urea was found to induce even less fragmentation, although at the expense of the total ion yield. Molecular ions of a noncovalent complex (vancomycin + diacetyl-L-Lys-D-Ala-D-Ala) have been observed for the first time in MALDI-FTMS. 2.94 microm infrared (IR) MALDI also produced abundant molecular ions of a range of nonbiological samples, including C60 and C70 fullerenes as well as dimetal coordination complexes.