Patent ID: 7259371
Filing Date: 2007-08-21
Classification: H01J

Abstract:
1. A mass spectrometer comprising: an ion source for generating ions in a high-pressure region; a vacuum chamber comprising an inlet aperture for passing the ions from the high-pressure region into the vacuum chamber, and an exit aperture for passing ions from the vacuum chamber; a series of multipole ion guides between the inlet and exit apertures and each of the ion guides in the series having a predetermined cross-section for defining an internal volume, the series comprising at least a first ion guide positioned nearest the inlet aperture and a second ion guide positioned nearest the exit aperture; a power supply for providing a corresponding RF voltage to each of the ion guides for radially confining the ions within the internal volumes of the ion guides; wherein the configuration of the inlet aperture and the pressure difference between the ion source and the vacuum chamber provides a supersonic free jet expansion downstream of the inlet aperture, the supersonic free jet expansion comprising a barrel shock of predetermined diameter; and wherein the cross-section of the first ion guide and the corresponding RF voltage applied to the first ion guide are configured for accepting at least 50% of the predetermined diameter of the barrel shock of the supersonic free jet expansion.