Performance of Infrared Matrix-assisted Laser Desorption/Ionization Mass Spectrometry with Lasers Emitting in the 3 μm Wavelength Range

The performance characteristics of two lasers emitting in the mid infrared, an Er-YAG (2.94 μm wavelength, 80–90 ns pulse width), and an Er-YSGG infrared laser (2.79 μm wavelength, 80 ns pulse width), in matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI-MS) of biological macromolecules, is reported. Glycerol and succinic acid were used as matrices. In IR-MALDI sample consumption per laser shot typically exceeds that of UV-MALDI by about two orders of magnitude. Using glycerol as matrix, the reproducibility of the ion signals from shot to shot is comparable to the best values achieved in UV-MALDI. The same holds true for the precision and accuracy of the mass determination. For succinic acid all these values are significantly worse, due to the strong sample heterogeneity as typically found in dried droplet preparations. Metastable fragmentation is comparable for UV- and IR-MALDI in the low mass range, but is significantly less for the IR in the mass range above ca. 20 kDa, leading to an improved mass resolution and an extended high mass limit for IR-MALDI.