Development of a gated electrostatic ion trap for recirculating ions through a charge detection tube
The determination of the mass of large (> 1 megadalton) electrospray ions requires a mass spectrometer that operates at high resolution in order to resolve the large number of adjacent m/z states. An alternative analytical approach is to measure simultaneously the charge and velocity of individual ions. We have described the development of a technique to measure the charge on individual electrospray ions using a Faraday tube connected to a charge sensitive amplifier. The low-noise charge-measuring detector responds to the image charge of individual ions as they pass through a metal tube. It operates at a noise level of 50 electrons rms and readily measures ions carrying more than 250 charges. Ions carrying more than 100 charges are detected with this system; however, the measurement of the mass of ions carrying less than 250 charges is compromised by electronic noise associated with the amplifier. Improved precision for mass measurements could be gained from signal averaging as obtained from repetitious measurements of ion charge. Here we describe the recent development of a gated electrostatic ion trapping technique for determining the mass of megadalton and larger electrospray ions. The gated electrostatic trap consists of ion mirrors mounted at each end of a detector tube that captures the image charge signal of passing ions. The mirrors force ions to cycle back and forth many times through the detector tube, thus allowing repeated measurements of ion charge and velocity to be made. Voltages applied to the electrodes define potential valleys for reflecting ions into the detector tube. Ions are introduced into the trap by gating one of the mirrors to O volts, thus allowing ions to pass through the mirror and into the detector tube. The image charge signal of an entering ion enables the entrance mirror, thus closing the gate to the trap. The ion then passes back and forth through the detector tube many times until it acquires an unstable trajectory and collides with the detector tube. Trapping times as long 10 ms have been observed for ions in this trap which provided as many as 450 remeasurements of ion charge and velocity. The results presented here indicate that the gated electrostatic trapping technique provides significantly faster analyses and mass resolution comparable to gel electrophoresis for DNA ions in the megadalton size range when the sample is electrosprayed from a salt containing buffer.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6375
- Report Number(s):
- LBNL-40060; ON: DE00006375
- Resource Relation:
- Conference: 14th IMSC International Mass Spectrometry Conference, Tampere, Finland, August 25-29, 1997
- Country of Publication:
- United States
- Language:
- English
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