Chapter 2
New Excitation and Detection Techniques in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry 1,2
4
1
Downloaded by WEIZMANN INST OF SCIENCE on May 27, 2018 | https://pubs.acs.org Publication Date: November 23, 1987 | doi: 10.1021/bk-1987-0359.ch002
Alan G. Marshall , Tao-Chin Lin Wang , Ling Chen , and Tom L. Ricca
3
1
Department of Chemistry, Ohio State University, Columbus, OH 43210 Department of Biochemistry, Ohio State University, Columbus, OH 43210 Chemical Instrument Center, Ohio State University, Columbus, OH 43210
2
3
FT/ICR experiments have conventionally been carried out with pulsed or frequency-sweep excitation. Because the cyclotron experiment connects mass to frequency, one can construct ("tailor") any desired frequency-domain excitation pattern by computing its inverse Fourier transform for use as a time-domain waveform. Even better results are obtained when phase-modulation and time-domain apodization are used. Applications include: dynamic range extension via multiple-ion ejection, high-resolution MS/MS, multiple-ion simultaneous monitoring, and flatter excitation power (for isotope-ratio measurements). The analytically important features of Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometry (1) have recently been reviewed (2-9): ultrahigh mass resolution 01,000,000 at m/z < 200) with accurate mass measurement even in gas chromatography/mass spectrometry experiments; sensitive detection of low-volatility samples due to 1,000-fold lower source pressure than in other mass spectrometers; versatile ion sources (electron impact (EI), self-chemical ionization (self-CI), laser desorption (LD), secondary ionization (e.g., Cs -bombardment), fast atom bombardment (FAB), and plasma desorption (e.g., 252cf fission); trapped-ion capability for study of ion-molecule reaction connectivities, kinetics, equilibria, and energetics; and mass spectrometry/mass spectrometry (MS/MS) with a single mass analyzer and dual collision chamber. +
Ion Motion in Crossed Static Magnetic and Oscillating Electric Fields The basic principle of FT/ICR mass spectrometry is that a moving ion in an applied static magnetic field undergoes circular motion, in a plane perpendicular to that f i e l d , at a "cyclotron" frequency, UJ, 4
Current address: Section on Analytical Biochemistry, Building 10, Room 3D-40, National Institute of Mental Health, 9000 Rockville Pike, Bethesda, M D 20892 0097-6156/87/0359-0021 $06.00/0 © 1987 American Chemical Society
Buchanan; Fourier Transform Mass Spectrometry ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
22
FOURIER TRANSFORM MASS SPECTROMETRY
3>
c
= qB/m
(1)
in which Β is the magnetic f i e l d strength (Tesla), q is the ionic charge (Coul), and m is the ionic mass (kg). The cyclotron motion is excited and detected as shown schematically in Figure 1 (10). First, i f an electric f i e l d oscillating (or rotating) at an angular frequency, (*>(=2τπί, in a plane perpendicular to the magnetic field axis, then "resonant" ions (i.e., those for which w =
