Multipole ion guide for mass spectrometry

Details Multipole ion guide for mass spectrometry Multipole ion guide for mass spectrometry

1999-08-12

2001-02-13

Anderson, Bruce C. (Department: 2878)

Radiant energy

Ionic separation or analysis

With sample supply means

C250S281000

Reexamination Certificate

active

06188066

ABSTRACT:

FIELD OF INVENTION
This invention relates to the configuration and method of using a multipole ion guide to transport and focus ions which enter vacuum from an atmospheric pressure ion source, into a mass analyzer. The multipole on guide which begins in one vacuum pumping stage has been configured to extend contiguously through one or more subsequent vacuum stages. Multipole ion guides are used to efficiently transfer ions through one or more vacuum stages while allowing the neutral background gas to be pumped away. The AC frequency and AC and DC voltages which are applied to the poles of a multipole ion guide can be set so that the multipole ion guide will pass a selected range of ion mass to charge. The ion transmission properties of multipole ion guides can be used to enhance performance of specific mass analyzer types which are interfaced to atmospheric pressure ion sources.
BACKGROUND OF THE INVENTION
Atmospheric pressure ion sources (API) have become increasingly important as a means for generating ions used in mass analysis. Electrospray or nebulization assisted Electrospray (ES), Atmospheric Pressure Chemical Ionization (APCI) and Inductively Coupled Plasma (ICP) ion sources produce ions from analyte species in a region which is approximately at atmospheric pressure. The ions must then be transported into vacuum for mass analysis. A portion of the ions created in the API source are entrained in the bath gas API source chamber and are swept into vacuum along with a the bath or carrier gas through an orifice into vacuum. Mass spectrometers (MS) generally operate in a vacuum maintained at between 10
−4
to 10
−10
torr depending on the mass analyzer type. The gas phase ions entering vacuum from an API source must be separated from the background carrier gas and transported and focused through a single or multiple staged vacuum system into the mass analyzer. Variations in vacuum system and associated electrostatic lens configurations have emerged in API/MS systems. Where multiple pumping stages have been employed, the electrostatic lens elements have been configured to serve as restricted orifices between vacuum stages as well as providing ion acceleration and focusing of ion into the mass analyzer. Performance tradeoffs may occur where electrostatic lenses must also accommodate restricting the neutral gas transmission from one pumping stage to the next. For example, a skimmer placed between one pumping stage and the next may restrict the neutral gas flow but may also restrict the passage of ions as well due to its relatively small orifice. Two types of Electrostatic elements have been used to transport and focus ions in vacuum, particularly where ions are entering vacuum from atmospheric pressure through a free jet expansion. The first is a static voltage lens and the second is a dynamic field ion guide. The most effective lens configurations used in API/MS systems employ a judicious combination of both elements which have static and dynamic fields applied.
The first electrostatic lens type has a fixed or static DC voltage applied during the time an ion is traversing the lenses' field.
FIG. 1
is a diagrammatic representation of a four pumping stage API/MS system with static voltage electrostatic lenses. Gas emerging from the capillary exit
8
into vacuum expands as a supersonic free jet and a portion of the gas passes through the first
10
and second
14
skimmer. Skimmers between pumping stages typically have small orifices to restrict the neutral gas flow into each downstream vacuum stage. DC voltages are applied to the capillary exit, skimmers and other electrostatic lenses
9
,
14
,
15
,
16
and
17
with values set to maximize the ion transmission into the mass spectrometer. Ions entrained in the expanding gas follow trajectories that are driven by a combination of electrostatic and gas dynamic forces. Strong influence from the gas dynamics can extend up to and beyond the second skimmer
13
for the configuration shown in Figure one. The efficiency of ion transmission through a static voltage lens set can be reduced by scattering losses due to collisions between ions and the background gas which occur along the ion trajectory. Ions with different m/z may vary their collisional cross sections and hence experience different numbers of background collisions as they are transported through vacuum. For a given electrostatic lens voltage setting the efficiency of ion transport into the mass spectrometer may vary with m/z or the collisional cross section. Changing the lens voltage values may optimize transmission for a given ion species but the setting may not be optimal for another ion species transmission. For example static lens configurations used in API/MS applications may not transmit lower molecular mass compounds as efficiently as higher molecular mass compounds. The smaller ions may sustain higher transmission losses due to collisional scattering from the background gas than the higher molecular mass compounds. To increase ion transmission efficiency through a static lens stack, the electrostatic energy must be set sufficiently high so that ions can be driven through the background gas. Static voltage lens configurations also tend to focus ions of different energy at different focal points. If the focal point is not located at the mass spectrometer entrance transmission losses can occur. To overcome the mass to charge transmission discrimination effects and ion transport inefficiencies which occur when static voltage lenses are used, multipole dynamic field ion guides have been employed to transport ions through vacuum pumping stages in the vacuum region of API/MS systems. The dynamic electrostatic fields within a multipole ion guide dominate over the background gas scattering collisions and effectively “trap” the ions while they traverse the length of the multipole ion guide.
The use of multipole ion guides has been shown to be an effective means of transporting ions through vacuum. Publications by Olivers et. al.(Anal. Chem, Vol. 59, p. 1230-232, 1987), Smith et. al. (Anal. Chem. Vol. 60, p.436-441, 1988) and U.S. Pat. No. 4,963,736 (1990) have reported the use of a quadrupole ion guide operated in the AC-only mode to transport ions from an API source into a quadrupole mass analyzer. U.S. Pat. No. 4,963,736 describes the use of a multipole ion guide in either vacuum pumping stage two of a three stage system or in the first pumping stage of a two stage vacuum system. This patent also reports that increasing the background pressure up to 10 millitorr in the vacuum stage where the ion guide was positioned resulted in an increase in ion transmission efficiency and a decrease in ion energy spread of ions transmitted. Ion signal intensity decreased for higher background pressures in the reported quadrupole configuration. A commercially available API/MS instrument manufactured by Sciex, a Canadian company, incorporates a quadrupole ion guide operated in the AC-only mode located before the quadruple mass filter in a single stage vacuum system. Ions and neutral gas flowing into vacuum through an orifice in the API source enter the quadrupole AC-only ion guide. The ions are trapped from expanding in the radial direction by the AC quadrupole fields and are transmitted along the quadrupole ion guide rod length as the neutral gas is pumped away through the rod spacing. Ions exiting the quadrupole ion guide are focused into a quadrupole mass filter located in the same vacuum chamber. Neutral gas is pumped away by a high capacity and relatively expensive cyro pump. Multiple quadrupole ion guides have been used to transport ions from API sources through multiple vacuum pumping stages and into a Fourier-Transform Ion Cyclotron Resonance mass analyzer. Beu et. al. (J. Am. Soc. Mass Spectrom vol. 4. 546-556, 1993) have reported using three quadrupole ion guides operated in the AC-only mode located in three consecutive vacuum pumping stages of a five pumping stage Electrospray Fourier-Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometer instrument. T

Affiliated with

Also associated with

Rating

Multipole ion guide for mass spectrometry does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Multipole ion guide for mass spectrometry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multipole ion guide for mass spectrometry will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2558104