A Gated Electrostatic Ion Trap To Repetitiously Measure the Charge and m/z of Large Electrospray Ions

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• 作者：W. Henry Benner
• 刊名：Analytical Chemistry
• 出版年：1997
• 出版时间：October 15, 1997
• 年：1997
• 卷：69
• 期：20
• 页码：4162 - 4168
• 全文大小：232K
• 年卷期：v.69,no.20(October 15, 1997)
• ISSN：1520-6882

文摘

The design and operation of a new type of ion trapprovides a way to measure mass, charge, and velocity oflarge individual electrospray ions (>1 MDa, >250charges)repeatedly during the time the ion is trapped. Thetrapconsists of an image charge detection tube mountedbetween two ion mirrors. The mirrors are sets ofparallelelectrodes drilled with holes aligned with the bore of thedetector tube. The device relies on voltages appliedtothe electrodes to establish symmetrically opposing ionfocusing mirrors for the purpose of cycling ions throughthe charge detection tube many times. This designdoesnot use magnetic or radio frequency fields to trap ions.Gating one of the mirrors to 0 V while maintainingvoltagesappropriate for reflecting ions on the opposite mirrorallows an ion to pass through the holes in the mirror andenter the detector tube. A low-noise charge-sensitiveamplifier, connected to the tube, reproduces the imagecharge of individual ions as they pass through thedetectortube. When a highly charged electrospray ion entersthedetector tube, its image charge triggers a circuit thatenables the entrance electrodes, thus closing the electrostatic gate to the trap. Ion mass is calculated fromsimultaneous measurements of ion charge and velocityevery time an ion passes through the detector.Individualions have been trapped for as long as about 10 ms, duringwhich time they cycled 450 times through the detectortube. At this level of trapping time, a theoreticalprecisionfor charge measurement as small as about two electronsrms can be achieved for 200 eV/charge ions carryingmore than 250 charges. The operation of the system isdemonstrated by trapping 2.88 MDa ions of DNA.