Patent ID: 7750312

Claim:
An ion source at a first pressure for generating ions by laser desorption/ionization for analysis by a mass analyzer, the mass analyzer having an inlet region aperture, and a vacuum chamber at a second, lower pressure than the first pressure of the ion source, comprising: a sample plate for supporting a sample deposited on the sample plate; a laser configured to generate laser pulses striking at least a portion of the sample on the sample plate, the laser pulses at an angle of incidence from about 0 to about 80 degrees to the center line of a first ion optical axis of the mass analyzer, adapted to produce a plume comprising analyte ions and neutral molecules; and a combination of the angle of incidence of the laser pulses and the distance between the sample plate and the inlet region aperture configured wherein the center of the plume is substantially directed away from the inlet region as the plume leaves the sample plate so as to reduce neutral molecules being drawn into the inlet region aperture due to gas flow resulting from the difference in pressure between the ion source region and the mass analyzer.