An Electrically Compensated Trap for Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Investigation and Charaxterization

Date of Award

Winter 12-15-2009

Author's School

Graduate School of Arts and Sciences

Author's Department


Degree Name

Doctor of Philosophy (PhD)

Degree Type



Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers the highest performance of any mass spectrometer. FT-ICR MS can routinely achieve mass measurement accuracies better than 5 ppm, while offering mass resolving powers that can be orders of magnitude higher than any other mass spectrometric technique. Nevertheless, there is still a need for improvement. One limitation arises from the finite dimensions of the electrodes that supply the trapping electric field that is necessary to confine the ions in a direction parallel to the magnetic field. The problem is the dependence of frequency on ion mode amplitudes or position (see Chapter 1). One strategy to combat this problem is mechanical or electrical trap compensation (see Chapter 2). The work described in this thesis implements an electrically compensated trap for reducing the inhomogeneities in the trapping electric field, thereby decreasing the positional dependence of frequency and increasing performance.

The compensated trap evaluated here was designed by Don Rempel and manufactured by the IonSpec Corporation. It has three pairs of auxiliary (compensation) ring electrodes to which independent voltages are applied. The superposition of the fields produced by these auxiliary ring electrodes creates a more ideal trapping electric field, which in the limit would be a three dimensional quadrupolar field. The outcome is a significant improvement in mass resolving power and signal-to-noise ratio when compared to an uncompensated or unmodified trap (see Chapter 3 and 5).

To obtain optimum performance from any electrically compensated trap, the compensation voltages applied must be tuned. We developed a tuning method (see Chapter 4) that efficiently and effectively tunes the compensation voltages on the basis of the experimentally observed cyclotron frequency centroids from ion clouds of different mode amplitudes. The compensation voltages require tuning to account for deviations from the theory used in the design process (see Chapter 7). As the electric field is improved by effective compensation, it becomes important to look at the variations in frequency caused by the magnetic field (see Chapter 6).

Another advantage that is offered by an electrically compensated trap is the ability to shape the electric field to suit new needs of an experiment. For example, electrical trap compensation may allow implementation of a highly-selective, non-destructive ion isolation event and high energy collisionally-activated dissociation in the ICR trap (see Chapter 8).


English (en)

Chair and Committee

Michael L. Gross

Committee Members

William E. Buhro, J. Dewey Holten, Richard Mabbs, Jay Turner, James Schilling


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