Abstract: A particle separation for use as an interface between a liquid chromatograph and a mass spectrometer comprises a vacuum chamber, an inlet nozzle for the chamber, a conical skimmer, and a vacuum exhaust port. The nozzle admits a stream of gas containing desolvated particles into a vacuum chamber as a supersonic jet. Heavier particles tend to concentrate near the central axis of the jet with lighter gas and vapor further from the axis. On entering the vacuum chamber, the jet forms a standing barrel shock wave extending from the nozzle to an aperture in the apex of the skimmer. The exterior angle formed by the conical surface of the skimmer is set so that the standing barrel shock wave attaches to the conical surface. The distance between the nozzle and the aperture is selected so that the skimmer pierces the downstream Mach disk of the shock wave so that the central particle beam enters the aperture without being perturbed by the mach disk.