VELOCITY DISTRIBUTIONS OF INTACT HIGH MASS POLYPEPTIDE MOLECULE IONS PRODUCED BY MATRIX ASSISTED LASER DESORPTION

The velocity distributions of polypeptide molecule ions (molecular mass 1000-15600 u) produced by matrix assisted ultraviolet laser desorption were measured using a modified time-of-flight mass spectrometer. The data demonstrate that polypeptide molecule ions produced by matrix assisted laser desorption at the ion production threshold irradiance have similar velocity distributions, with an average velocity of approximately 750 m/s. This result has important implications for the design of mass spectrometers that use the effect to generate polypeptide molecule ions and for the theoretical treatment of the laser desorption process. A jet expansion model for the desorption of high mass polymers is proposed to explain the results.