Mass spectrometer having an ion guide with an axial field

A mass spectrometer comprising:

• (a) an ionization source configured to ionize molecules;
• (b) an ion guide configured to receive the ionized molecules, the ion guide comprising;
• (i) a plurality of electrodes arranged about a device centerline to form an internal volume, at least two of the electrodes including a longitudinally extending gap, in which the longitudinally extending gap splits the electrode into two portions displaced from one another, the electrodes including an inward surface facing the device centerline to form a periphery of the internal volume;
• (ii) a plurality of resistive inserts, each configured to be proximate to a gap, and radially aligned with respect to the device centerline, the resistive inserts including an innermost surface that faces the device centerline where the innermost surface is a first distance from the periphery of the internal volume;
• (iii) a RF voltage supply configured to apply a RF voltage to the plurality of electrodes that establishes a RF field to radially confine ions, wherein the RF voltage supply is also configured to apply the RF voltage to the plurality of resistive inserts;
• and
• (iv) a DC voltage supply configured to apply a first DC voltage to a first location of the resistive insert and a second DC voltage to a second location of the resistive insert that establishes an axial electric field gradient along at least a portion of the device centerline, in which the second DC voltage is different than the first DC voltage and the second location is longitudinally spaced apart from the first location.
• (c) a mass analyzer configured to receive the ionized molecules from the ion guide and filter the ionized molecules so that a subset of ionized molecules having a particular mass to charge ratio passes through;
• and
• (d) a detector configured to receive and measure the ionized molecules from the mass analyzer.

An ion guide comprising:

• (a) a plurality of electrodes arranged about a device centerline to form an internal volume, the internal volume including a front end configured to allow ions to enter and a back end configured to allow ions to exit, where at least two of the electrodes including a longitudinally extending gap, in which the longitudinally extending gap splits the electrode into two portions displaced from one another, the electrodes including an inward surface facing the device centerline to form a periphery of the internal volume;
• (b) a plurality of conductive inserts each configured to be proximate to a gap, the conductive inserts including an innermost surface that faces the device centerline where the innermost surface includes
• (i) a first distance from the periphery of the internal volume at the front end, and
• (ii) a second distance from the periphery of the internal volume at the back end, the first distance being greater than the second distance;
• (c) a RF voltage supply configured to apply a RF voltage to the plurality of electrodes that establishes a RF field to radially confine ions, wherein the RF voltage supply is also configured to apply the RF voltage to the plurality of conductive inserts;
• and
• (d) a DC voltage supply configured to apply a DC voltage to the conductive inserts that establishes an axial electric field gradient to move ions along the device centerline.

A method of guiding ions in a mass spectrometer, the method comprising:

• (a) injecting ions into an ion guide, the ion guide comprising:
• (i) a plurality of electrodes arranged about a device centerline to form an internal volume, the internal volume including a front end configured to allow ions to enter and a back end configured to allow ions to exit, where at least two of the electrodes including a longitudinally extending gap, in which the longitudinally extending gap splits the electrode into two portions displaced from one another;
• (ii) a plurality of inserts, each configured to be proximate to a gap, the inserts including an innermost surface that faces the device centerline where the innermost surface includes a first distance from the device centerline;
• (b) applying a RF voltage to the plurality of electrodes that establishes a RF field to radially confine ions;
• (c) applying the RF voltage to the plurality of inserts;
• and
• (d) applying at least one DC voltage to the plurality of inserts that establishes an axial electric field gradient along at least a portion of the device centerline.