Matrix-assisted laser desorption/ionization with nitrogen lasers of different pulse widths

The effect of the laser pulse width has been investigated for matrix-assisted laser desorption/ionization (MALDI) of analyte and matrix ions as well as for (photoionized) neutral matrix molecules by comparing two nitrogen lasers (337 nm) with 0.55 and 3 ns pulse widths as commonly used for MALDI mass spectrometry. A homogeneous ''flat-top'' laser beam profile was used in these experiments. Neither did the threshold fluences (minimum incident laser energy per unit area for producing a spectrum) change, nor was there a difference in the increase in ion signal intensity with laser fluence between the two lasers. Also, no significant differences were found in the mass spectra. The results show that 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.