Direct comparison of infrared and ultraviolet wavelength matrix-assisted laser desorption/ionization mass spectrometry of proteins
- 140 Downloads
In an effort to gain an understanding of the processes governing matrix-assisted laser desorption/ionization (MALDI), we made a direct comparison of ultraviolet (UV)- and infrared (IR)-MALDI linear time-of-flight mass spectra of proteins obtained from the same samples and matrices (on the same sample surface), using two different lasers, each having short duration (<10-ns) pulses, i.e., a tunable wavelength Nd:yttrium aluminum garnet (YAG) pumped optical parametric oscillator laser operating at 2.94 µm and a Nd:YAG laser operating at 355 nm. We observed that (1) the IR-MALDI and UV-MALDI spectra of a given protein from the same matrix were strikingly similar; (2) protein ions produced by IR-MALDI experienced less fragmentation than those produced by UV-MALDI; and (3) photochemical adducts produced during UV-MALDI were absent in IR-MALDI. These results lead us to speculate on the mechanisms for the ionization process in UV- and IR-MALDI. Because photons with a wavelength of ∼3 µm are unlikely to effect electronic excitation of the matrix at the irradiance used for MALDI, we propose that ionization in IR-MALDI occurs as a natural consequence of the solid-to-gas phase transition induced by the IR irradiation, and involves proton transfer reactions in the intermediate phase between solid and gas. The strikingly similar UV- and IR-MALDI mass spectra leads us to the additional proposal that ionization in UV-MALDI may also be a natural consequence of the phase transition and that electronic excitation may not play a primary role in the ionization process.
KeywordsMALDI Succinic Acid Yttrium Aluminum Garnet Optical Parametric Oscillator Laser Shot
Unable to display preview. Download preview PDF.
- 4.Hillenkamp, F.; Karas, M.; Beavis, R. C.; Chait, B. T. Anal. Chem. 1991, 63, 1193A.Google Scholar
- 12.Hillenkamp, F.; Karas, M.; Berkenkamp, S. Proceedings of the 43th ASMS Conference on Mass Spectrometry and Allied Topics Atlanta, GA, 1995, 357.Google Scholar
- 26.Beavis, R. C.; Chait, B. T. In Methods and Mechanisms for Producing Ions from Large Molecules; Standing, K. G.; Ens, W., Eds.; Plenum: New York, 1991, 227.Google Scholar
- 32.Zhang W.; Niu S.; Chait B. T.; unpublished.Google Scholar
- 37.Verentchikov, A.; Ens, W.; Martens, J.; Standing, K. G. Proceedings of the 40th ASMS Conference on Mass Spectrometry and Allied Topics; Washington, D. C.; 1992; 360.Google Scholar
- 38.Johnson, R. E. In Large Ions: Their Vaporization, Detection and Structural Analysis Bear, T.; Ng, C. Y.; Powis, I., Eds.; Wiley: New York, 1996; Chap 3.Google Scholar
- 40.Berkenkamp, S.; Menzel, C.; Rohling, U.; Strupat, K.; Hillenkamp, F. Presented at the 14th International Mass Spectrometry Conference, Tampere, Finland; August, 1997.Google Scholar
- 42.Chen,X.; Beavis,R. C. Presented at the 45th ASMS Conference on Mass Spectrometry and Allied Topics; Palm Springs, 1997.Google Scholar