Apparatus and methods for reduced neutral contamination in a mass spectrometer

Apparatus for reducing contamination in a mass spectrometer, comprising:

• an ionization chamber for generating a beam of ions;
• an ion guide having a quadrupole rod set including a plurality of rods arranged in a quadrupole configuration and spaced from one another to provide a channel through which ions generated in the ionization chamber can be transmitted to one or more downstream mass analyzers, the ion guide channel comprising a guide inlet aperture in communication with said ionization chamber and a guide exit aperture for passing ions to said downstream mass analyzers,
• a power supply for providing voltage to one or more of said plurality of rods for confining the ions within an internal volume of the ion guide channel;
• and
• a curtain gas inlet for introducing an internal curtain gas into the ion guide channel at a volumetric flow rate of at least 0.1 standard liter per minute (slpm), such that the internal curtain gas flow facilitates removal of the neutral molecules,
• wherein the ion guide channel inlet aperture is configured to allow generation of a supersonic free jet expansion comprising a barrel shock of predetermined diameter downstream of the inlet aperture, and wherein a cross-section of the ion guide channel defined by a radial distance between two radially opposed rods of the quadrupole rod set is sized to be at least 50% of the predetermined diameter of the barrel shock of the supersonic jet expansion.

A method for controlling contamination in a mass spectrometer system, comprising:

• generating one or more ionized species from a sample within an ionization chamber;
• directing an ion stream comprising ions generated in the ionization chamber through a channel of an ion guide having a plurality of rods arranged in a multipole configuration and spaced from one another to provide the channel to one or more downstream mass analyzers, the ion guide channel comprising an inlet aperture in communication with said ionization chamber and an exit aperture for passing ions to said downstream mass analyzers;
• and
• introducing an internal curtain gas into the ion guide channel at a volumetric flow rate of at least 0.1 standard liter per minute (slpm) flowing in a contra flow direction to the ion stream, such that internal curtain gas flow facilitates removal of neutral molecules from the ion stream.