Quadrupole ion trap mass spectrometry: theory, simulation, recent developments and applications

Abstract

This paper is a presentation of recent key developments in quadrupole ion trap mass spectrometry. These key developments have been made in three areas; namely, the trapping of ions generated externally to the ion trap, the fine control of the trajectories of ions confined within the ion trap, and the ejection of ions from the ion trap. Applications of quadrupole ion trap mass spectrometry that are illustrative of these developments are discussed. The origin of the quadrupole ion trap and its mode of current usage are discussed briefly. # 1998 John Wiley & Sons, Ltd. Received 20 June 1998; Revised 7 August 1998; Accepted 9 August 1998 The original commercial usage of a quadrupole ion trap was limited to the formation of ions in situ by electron impact ionization, focusing of the nascent ions to a cloud at the centre of the ion trap, and mass-selective axial ejection of ions to form a mass spectrum. The sheer simplicity of the mass-selective axial ejection technique permitted the commercialization of the quadrupole ion trap as a massselective detector for compounds separated by gas chromatography. In the past 15 years, the field of quadrupole ion trap mass spectrometry has developed appreciably; while it is not possible to consider all developments, attention can be focused on the key developments that extend or enhance ion trap performance markedly. The key instrumental developments cover three main areas: (a) the injection and storage of ions generated externally to the ion trap; (b) the fine control of the trajectories of ions confined within the ion trap; (c) the ejection of ions from the ion trap.

Intramolecular condensation reactions in protonated dipeptides: Carbon monoxide, water, and ammonia losses in competition

“…These conditions led to intense [M ϩ H] ϩ ions. CAD tandem mass spectra (MS 2 ) of [M ϩ H] ϩ were acquired by ejecting all ions from the trap except [M ϩ H] ϩ , which was then excited to fragment with a radiofrequency field that was turned on for 40 ms at an amplitude (V p-p ) of 0.4 -0.6 V; the [M ϩ H] ϩ ions were accelerated by the RF field and underwent CAD with the helium buffer gas in the trap [30,34]. MS 3 spectra were obtained by isolating in the trap a fragment from [M ϩ H] ϩ (formed as described) and following the same procedure as with the isolated [M ϩ H] ϩ .…”

“…In our high-energy CAD experiments (keV range), a broad range of internal energies is deposited by a single collision onto the precursor ion which subsequently dissociates in less than a few microseconds; under these conditions, several competitive dissociations can take place simultaneously, depending on the amount of energy gained by a particular precursor ion and the dissociation kinetics [43]. Conversely, low-energy CAD in the trap activates by multiple collisions, each depositing a small amount of internal energy, while millisecond time windows are available for dissociation between collisions [29,30,34]. Once the threshold for a fast reaction is reached, the precursor ion reacts by this channel accumulating the corresponding fragment ion.…”

Fragmentation of ions in a low pressure linear ion trap

“…The duration of the excitation periods can be reduced and the excitation amplitudes increased without loss of the precursor ion by increasing the content of the higher order fields. This can be done with the use of additional electrodes along the length of the LIT [14] or by distorting the physical dimensions of the quadrupole electrodes for the purposes of introducing additional higher order fields into the radial trapping potential [4,8,15].It was noted by Michaud et al [15] that in their experiments the fragmentation efficiency of reserpine at q ϭ 0.20 was significantly less efficient than that observed by Collings et al [7] at a slightly higher excitation q of 0.21 when using an LIT constructed from a conventional round rod quadrupole array. It was speculated that one contributing factor may have been the difference in drive frequencies, 768 kHz for their experiments and 816 kHz for the experiments of Collings et al, leading to a significant difference in the pseudopotential well depths, 6.4 and 8.0 eV respectively.…”

“…In this device, the second mass analyzing quadrupole doubles as the LIT. The LIT typically operates at pressures in the 3-5e-5 torr range, which is significantly lower than the mTorr pressure regime typically used for the operation of 3-D ion traps [3,4] and other high-pressure LITs [5,6]. This difference is a key factor in how in-trap fragmentation of ions, through the use of dipolar excitation, is performed [7].…”

“…The duration of the excitation periods can be reduced and the excitation amplitudes increased without loss of the precursor ion by increasing the content of the higher order fields. This can be done with the use of additional electrodes along the length of the LIT [14] or by distorting the physical dimensions of the quadrupole electrodes for the purposes of introducing additional higher order fields into the radial trapping potential [4,8,15].…”