MATRIX-ASSISTED LASER DESORPTION IONIZATION WITH NITROGEN LASERS OF DIFFERENT PULSE WIDTHS/

The effect of the laser pulse width has been investigated for matrix-a ssisted laser desorption/ionization (MALDI) of analyte and matrix ions as well as for (photoionized) neutral matrix molecules by comparing t wo nitrogen lasers (337 nm) with 0.55 and 3 ns pulse widths as commonl y used for MALDI mass spectrometry. A homogeneous ''flat-top'' laser b eam profile was used in these experiments. Neither did the threshold f luences (minimum incident laser energy per unit area for producing a s pectrum) change, nor was there a difference in the increase in ion sig nal intensity with laser fluence between the two lasers. Also, no sign ificant differences were found in the mass spectra. The results show t hat the desorption/ionization process is essentially determined by the energy supplied in the studied pulse width range, rather than by the rate of energy flow into the sample.