INITIAL VELOCITIES OF POSITIVE AND NEGATIVE PROTEIN MOLECULE-IONS PRODUCED IN MATRIX-ASSISTED ULTRAVIOLET-LASER DESORPTION USING A LIQUID MATRIX

The initial axial velocities for the positive and negative cytochrome c molecule-ions desorbed from a liquid matrix (3-nitrobenzyl alcohol) using a 17 ns ultraviolet laser (266 nm) have been determined. The met hod employed was based upon measurement of ion flight times through a field-free path co-axial with the ion optical axis. The possible inter ferences, such as energy deficits, due to the presence of electric fie lds were avoided by using a grid-electrode placed at a very short dist ance from the sample stage. The potential of this electrode was mainta ined at the same potential as the sample stage, thereby creating a nar row field-free region within which ion generation took place. Systemat ic variations of the potential at a second grid-electrode caused a gra dual shift of the ion flight times, which could be related to the init ial ion velocities. The ion velocities were obtained by correlating th e measured time-shifts with values from theoretical analysis. The posi tive and negative molecule-ions were found to have axial velocities of 840 +/- 70 and 750 +/- 40 ms-1, respectively.