Patent ID: 9396919
Filing Date: 2016-07-19
CPC Classification: H01J

Claim Text:
1. A method of operating a gas-filled collision cell in a mass spectrometer, the collision cell having a longitudinal axis extending between a first end and a second end, the method comprising: causing ions to enter the collision cell through the first end in a forward direction; generating a trapping field within the collision cell so as to trap the ions within a trapping volume of the collision cell, the trapping volume being defined by the trapping field and extending along the longitudinal axis; ejecting trapped ions from the collision cell in the forward direction through the second end; causing the ejected ions to re-enter the collision cell in the reverse direction through the second end; and ejecting ions from the collision cell in a reverse direction through the first end, wherein the method further comprises providing a DC potential gradient, using an electrode arrangement, resulting in a non-zero electric field at all points along the axial length of the trapping volume so as to cause ions to exit the collision cell in the reverse direction, wherein the direction and magnitude of the DC potential gradient remains the same during the steps of generating the trapping field, and ejecting ions in the reverse direction.