Development of an Electrostatic Linear Ion Trap for Tandem Mass Spectrometry
Abstract
The electrostatic line ion trap (ELIT) is a relatively new type of mass analyzer in which ions are axially confined between two opposing ion mirrors. Image charge induced on a central pick-up electrode can be digitized, mass analyzed, and calibrated to produce a mass spectrum. Recent improvements to the ELIT and the development of a novel high resolution, high efficiency ion isolation method have given new life to the use of the ELIT as high-performance tandem mass spectrometer. This dissertation outlines advancements in all areas of tandem mass spectrometry (ion isolation, probing ions, and mass analysis) using an electrostatic linear ion trap. An introduction to the ELIT and the analytical techniques associated with the device is discussed in Chapter 1. Next, Chapters 2 and 3 discuss innovations in the realm of mass analysis using an ELIT. Following discussion of the mass analyzer, Chapter 4 discusses a novel high resolution, high efficiency method for ion isolation. Chapter 5 then discusses an extension of the fore-mentioned ion isolation method in which multiple ions can be isolated simultaneously. Finally, Chapter 6 discusses tandem mass spectrometry experiments that have been done with the current iteration of the ELIT. In Chapter 2, the ELIT was configured to allow for the simultaneous acquisition of mass spectra via Fourier transform (FT) techniques (frequency measurement) and via time-of-flight (TOF; time measurement). In the former case, the time-domain image charge derived from a pick-up electrode in the field free region of the ELIT is converted to frequency-domain data via Fourier transform (FT-ELIT MS). The ELIT geometry facilitates the acquisition of both types of data simultaneously because the detection schemes are independent and do not preclude one another. The two MS approaches exhibit a degree of complementarity. Resolution increases much faster with time with the MR-TOF approach, for example, but the closed-path nature of executing the MR-TOF in an ELIT limits both the m/z range and the peak capacity. For this reason, the FT-ELIT MS approach is most appropriate for wide m/z range applications, whereas MR-TOF can provide advantages in a “zoom-in’ mode in which moderate resolution (M/ΔMfwhm≈ 10,000) at short analysis time (10 ms) is desirable. In Chapter 3, the mass resolution of the FT-ELIT experiment is increased by reducing the axial length of the ELIT. Mass resolution increases linearly with frequency. For an equivalent transient length, which implies an equivalent path length, resolution is higher in a shorter ELIT. Relative changes in the m/z range were also explored. When trapping ions using mirror switching, the m/z range is determined by the time required for fast ions to enter and exit the trap (one reflection), and the time it takes slow ions to enter the trap. By reducing the length of the FT-ELIT mass spectrometer while maintaining a constant distance from the point ions are initially accelerated to the first ion mirror, only the low m/zlimit is affected for a given mirror switching time. Both a 2.625” and a 5.25” trap will be examined and compared.
Degree
Ph.D.
Advisors
McLuckey, Purdue University.
Subject Area
Energy|Analytical chemistry|Chemistry|Mathematics|Pharmaceutical sciences
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