Methods and apparatus for spatial separation of AC and DC electrical fields with application to fringe fields in quadrupole mass filters

Claim 2

In a method of mass analysis which utilizes a quadrupole mass filter which comprises the steps of producing ions, causing the introduction of said ions into the space between the poles of the quadrupole mass filter, and causing the transmission of only those ions of a selected mass-to-charge ratio through the space between said poles, the improvement comprising the use of a field separation means adjacent at least one of the end of said poles composed of a material which functions substantially as a high dielectric to ac electric fields and substantially as a conductor to substantially dc electric fields emanating from said pole, said separation means configured to allow said transmission of ions and to shield them during said transmission at least in part from the substantially dc electric fields.

Claim 3

A method in accordance with claim 1, wherein said material which is providing said shielding during said transmission of the ions has a dielectric constant of between about 1 and 50, a magnetic permeability of between about 1 and 1,000, and a resistivity in excess of about 105 ohm-cm but not so high as to be unable effectively to conduct away current caused by ions striking the material during said transmission of ions.

Claim 4

A method in accordance with claim 1 wherein said field separation means is located proximate the entrance end of said poles for the receipt and said shielding of ions transmitted into the mass filter.

Claim 5

A method in accordance with claim 1 wherein said field separation means is located near the exit end of said poles for said shielding of ions transmitted from the pole structure of the mass filter.

Claim 6

In a method for improving the efficiency of injection and/or transmission of ions passing through quadrupole mass filters which comprises the steps of producing ions and transmitting ions into, through and from the region between the poles of the quadrupole mass filter, the improvement comprising the use of field separation means placed at at least one end of the mass filter pole structure, said field separation means being composed of material which functions substantially as a high dielectric to the ac fields and substantially as a conductor to the substantially dc fields of the mass filter, said field separation means configured to permit said transmission of ions and to shield the ions in said transmission at least in part from said substantially dc fields, the geometries of the arrangement being such as to make the ac fringe fields at a given relative field strength in space extend relatively farther away from the ends of the mass filter than the dc fringe fields wherein the relative fringe field strength is defined as the strength of the field at a given point divided by the strength of the corresponding field within the mass filter electrode structure.

Claim 7

In a method for improving the efficiency of injection and/or transmission of ions passing through quadrupole mass filters which comprises the steps of producing ions and transmitting ions into, through and from the region between the poles of the quadrupole mass filter, the improvement comprising the use of field separation means placed at at least one end of the mass filter pole structure, said field separation means being composed of material which functions substantially as a high dielectric to the ac fields and substantially as a conductor to the substantially dc fields of the mass filter, said field separation means configured to permit said transmission of ions and to shield the ions in said transmission at least in part from said substantially dc fields, the geometries of the arrangement being such as to make the ac fringe fields at a given relative field strength in space extend relatively farther away from the ends of the mass filter than the dc fringe fields wherein the relative fringe field strength is defined as the strength of the field at a given point divided by the strength of the corresponding field within the mass filter electrode structure.

Claim 8

A method in accordance with claim 5 wherein said field separation means providing said shielding for ions is placed at the entrance of the mass filter pole structure.

Claim 11

A device in accordance with claim 7 wherein said tube is inserted into the entrance end into said space between the four electrodes of the mass filter.

Claim 12

A device in accordance with claim 7 wherein said tube is substantially cylindrical in form.

Claim 13

A device in accordance with claim 7 wherein said tube is substantially in the form of a truncated cone.

Claim 14

A device in accordance with claim 7 wherein said material is a leaky dielectric which has a dielectric constant of between about 1 and 50, a resistivity in excess of about 105 ohm-cm but not so high as to be unable to conduct away any ion current which may strike the material and a magnetic permeability between 1 and 1,000.

Claim 15

A device in accordance with claim 11 wherein said material is a homogeneous ferrite.

Claim 18

A device in accordance with claim 13 wherein said material is a leaky dielectric which is characterized by having a dielectric constant of between about 1 and 50, a resistivity in excess of about 105 ohm-cm but not so high that it is unable effectively to conduct away ion currents that might strike the material and a magnetic permeability of between about 1 and 1, 000.

Claim 19

A device in accordance with claim 14 wherein said end comprises the entrance end into the quadrupole mass filter electrode structure.

Claim 22

A device in accordance with claim 16 wherein said material is homogeneous.

Claim 23

A device in accordance with claim 16 wherein said material is a leaky dielectric which is characterized by having dielectric constant in the range of about 1 and 50, resistivity in excess of 105 ohm-cm but not so high that it it is unable effectively to conduct away current caused by ions striking the pieces of material and a magnetic permeability in the range of about 1 and 1,000.

Claim 24

A device in accordance with claim 18 wherein said material is a ferrite.