Broad-band excitation and non-destructive detection of ions in an ion trap mass spectrometer

Manish Haridatt Soni, Purdue University

Abstract

The quadrupole ion trap mass spectrometer has seen a remarkable transformation from an obscure GC detector to a high performance bench-top mass spectrometer over the last decade and a half. This thesis describes several techniques that further extend its performance characteristics and capabilities. The ion trap is inherently susceptible to deleterious space-charge effects arising from interactions between an excess of trapped ions. However, these effects can be minimized by using selective broad-band resonance excitation to remove unwanted ions and restrict ion storage only to ions of interest. Broad-band excitation is performed using notched waveforms created by the stored waveform inverse Fourier transform (SWIFT) technique. In addition to mass-selective ion injection, storage and accumulation this technique is also utilized for broad-band ion isolation, tandem mass spectrometry, selected ion monitoring (SIM), multiple ion monitoring (MIM) and in mass-selected ion/molecule reaction experiments. A two-step ion isolation method is demonstrated for unit-mass isolations at high mass range. Practical applications of this method are shown in conjunction with membrane introduction mass spectrometry using bench-top ion traps. Another area of research focuses on a new technique for detecting trapped ions in an ion trap mass spectrometer. In this method, an auxiliary detector electrode is used as an antenna to receive image currents from a coherently oscillating ion population. The image currents are directly measured using a broad-band differential preamplifier, filter and amplifier. Fourier analysis is used to obtain frequency (hence mass) spectra that are characteristic of the trapped ions. The method is inherently non-destructive of the ions under study. This allows further studies and multiple measurements of the same ion population. We call this method Fourier transform ion trap mass spectrometry (FT-ITMS). The first demonstrations of broad-band non-destructive detection of ions in an ion trap mass spectrometer are described.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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