An apparatus and method for generating analyte ions from a sample. An ion generating device is provided having a chamber with an outlet and a surface having a material and means for applying a high velocity gas flow through the chamber toward the outlet such that charged particles are produced by physical interaction between the high velocity gas and the material. The charged particles then induce the generation of primary ions by interaction with molecules of the high velocity gas. The primary ions are emitted from the outlet of the ion generating device toward a sample-bearing surface and analyte ions are generated by impact of the primary ions on the analyte sample on the surface.