IR-MALDI of low molecular weight compounds using a free electron laser

Initial experiments on infrared matrix-assisted laser desorptionrionization mass spectrometry IR-MALDI.using a free electron laser in the analysis of low-molecular-weight compounds are reported. Mass spectra from samples of ethylenedi- aminetetraacetic acid EDTA., nitrilotriacetic acid NTA.and a phosphate salt were obtained. Low molecular weight LMW.compounds are of similar mass as the molecular weight of the matrix compound and interference between matrix and analyte ions can degrade MALDI sensitivity. Under optimal conditions, however, we find little interference and that often the analyte signal exceeds the matrix signal, a result also observed in UV-MALDI of these compounds. In the IR-MALDI of EDTA near 3.0 mm the FEL results are similar to those obtained using a fixed frequency 2.94 mm Er:YAG laser of 200 ns pulse duration. However, the tunable FEL laser can selectively excite particular vibrational modes of the matrix e.g., an OH or CO stretch.or of residual water contained within the crystalline MALDI sample. This capability was used to explore possible vaporization and ionization mechanisms of IR-MALDI for EDTA. q1998 Pacific Northwest National Laboratory. Published by Elsevier Science B.V.