Biomedical subjects

RG Cooks

Publications and source records attributed to RG Cooks.

5 recordsLinked to original sources

PubMed2000

Cylindrical ion trap array with mass selection by variation in trap dimensions

A mass spectrometer array is described in which each array element is a cylindrical ion trap (CIT) within which an approximately quadrupolar, time-varying, field is established. The individual traps are of different sizes, so that when the array is operated with a fixed rf potential, ions of different masses (or mass ranges) are stored in each trap. By choosing the dimensions of each CIT element in the array, a multiple ion monitoring experiment can be performed. For example, in a two-element array with elements having internal radii of 5 and 4 mm, the smaller trap selects for m/z 91 and the larger for m/z 57, corresponding to characteristic aromatic and aliphatic hydrocarbon ions. Ion storage using both rf/dc (apex) isolation and the stored waveform inverse Fourier transform method is demonstrated.The array reduces the complexity of the electronics needed to operate the ion trap, which should make it suitable for use in a miniature mass spectrometer system.

Journal Article↗

PubMed2000

A parallel miniature cylindrical ion trap array

A small mass spectrometer array is described in which each element is a cylindrical ion trap (CIT). The array contains four CITs, each having an inner radius of 2.5 mm, arranged in parallel and operated using a single electronics system under common conditions for trapping and mass analysis. By using an array of identically sized traps, higher ion capacity can be achieved than with a single miniature CIT, but the advantage of lower power and voltage requirements associated with the smaller ion trap is maintained. Overall signal intensity of the array of four traps is compared with that of a two-element CIT array to demonstrate the increased ion capacity of larger arrays. Resolution for m-dichlorobenzene is shown to be approximately 180 (full width at half-maximum), with no significant loss in resolution as a result of using multiple CITs. The detection of 5 x 10(-9) Torr partial pressure of krypton in argon with a signal-to-noise ratio of approximately 30 for the most abundant isotope is shown, demonstrating the applicability of the device for process gas monitoring. Also, a preliminary spectrum from a 10-CIT array with each element having an inner radius of 1.5 mm is reported.

Journal Article↗

PubMed2000

Control of chemical mass shifts in the quadrupole ion trap through selection of resonance ejection working point and rf scan direction

Compound-dependent chemical mass shifts are observed and their origin is elucidated in a modified Finnigan GCQ quadrupole ion trap mass spectrometer. The dependence of chemical mass shifts on ion trap geometry, specifically the center to end-cap spacing, z0, and the size of the apertures in the end caps, is demonstrated. The effects of the working point (qeject value) used for resonance ejection and the direction of the rf mass analysis scan are also studied, and the results are found to be in agreement with a previously proposed model for the chemical mass shift mechanism. It is shown that chemical mass shifts are present when resonance ejection is used, unless the qeject is chosen to correspond to a nonlinear resonance point, where the shifts are removed. The shifts are also removed by performing the mass analysis scan in the reverse direction, i.e., from high mass to low mass.

Journal Article↗

PubMed1999

Differential non-destructive image current detection in a fourier transform quadrupole ion trap

Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗

PubMed1999

Characterization of a serial array of miniature cylindrical ion trap mass analyzers

Two small (5 mm internal radius) cylindrical ion traps (CITs) are arranged in series and operated using a single ion source, detector and radio frequency (rf) trapping signal. Ions are trapped in the first CIT and later transferred to the second by applying a direct current (dc) pulse to the endcap electrode of the first trap. This process is facilitated if a second, appropriately timed, retarding dc pulse is applied to the exit endcap electrode of the second trap. Mesh endcaps are used for the CITs to increase the number of ionizing electrons entering the trap and to maximize the transfer efficiency and detected signal. The transfer efficiency is dependent on the amplitude of the dc potential applied to eject the ions from the first trap, the amplitude of the dc potential applied to retain the ions in the second trap, and the period during which the retarding potential is applied. The amplitude and phase of the rf also affect the transfer process. Ions that readily dissociate upon collision have low transfer efficiencies; more stable ions can be transferred with up to 50% efficiency. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗