Apparatus and method for providing ions to a mass analyzer

An ion transfer assembly for directing ions from an ionization source to a mass analyzer, comprising:

• a partition element for separating a first region from a second region, the partition element comprising:
• an aperture communicating from the first region to the second region for transmitting ions therebetween, the center of the aperture lying along a longitudinal axis passing through the mass analyzer;
• and,
• a skimmer cone formed by two electrode surfaces that are electrically isolated one from the other, the two electrode surfaces disposed in a facing relationship one relative to the other and such that the longitudinal axis passes therebetween;
• and,
• an ion transfer element disposed within the second region, the ion transfer element having an input end for receiving ions that have passed through the aperture of the partition element, wherein application of a potential difference between the two electrode surfaces of the partition element results in an electric field being established for deflecting the ions toward the input end of the ion transfer element.

A method for directing ions from an atmospheric pressure ionization source to a mass analyzer, comprising:

• producing ions in an atmospheric ionization source from a sample material;
• transferring some of the ions from the ionization source to a first region via a passageway that is in fluid communication with the ionization source, the passageway defining a first longitudinal axis along which the ions travel through the passageway;
• sampling some of the ions from the first region into a second region maintained at a pressure between 2 and 400 millitorr via an aperture that is defined through a partition element, the aperture centered about a second longitudinal axis that passes through an ion transfer element within the second region, the second longitudinal axis being laterally or angularly offset with respect to the first longitudinal axis;
• and,
• deflecting ions that pass through the aperture of the partition element toward the second longitudinal axis by establishing an electric field that is directed transverse to the first longitudinal axis, such that relatively more ions enter an input end of the ion transfer element compared to when the ions are not deflected;
• wherein the deflecting step includes applying a potential difference between two spaced-apart electrode surfaces, the two spaced-apart electrode surfaces being disposed one each on opposite sides of the longitudinal axis, so as to establish the electric field for deflecting ions.