Ion-trapping device

Rapid scanning mass spectrometers providing unit resolution are routinely used as chroaatographic detectors. Ion separation is accomplished using either a magnetic sector, quadrupole filter or ion trap device. Ions can also be separated by time-of-flight or ion cyclotron resonance mass analyzers but these devices are not widely used with chromatograidiic inlets and will not be discussed here [20]. 

Note Here, we are going beyond the domain of the classical mass spectro-metric time scale (Chap. 2.7). In ion trapping devices, ions are stored for milliseconds to seconds, i.e., 10 -10 times longer than their lifetimes in beam instruments. 

Ion trapping devices are sensitive to overload because of the detrimental effects of coulombic repulsion on ion trajectories. The maximum number of ions that can be stored in a QTT is about 10 -10, but it reduces to about 10 -10 if unit mass resolution in an RF scan is desired. Axial modulation, a sub-type of resonant ejection, allows to increase the number of ions stored in the QIT by one order of magnitude while maintaining unit mass resolution. [160,161] During the RF scan, the modulation voltage with a fixed amplitude and frequency is applied between the end caps. Its frequency is chosen slightly below V2 of the fundamental RF frequency, because for Pz < 1, e.g., = 0.98, we have z = (0 + 0.98/2) = 0.49 x... 

Elemental mass spectrometry has undergone a major expansion in the past 15-20 years. Many new a, elopments in sample introduction systems, ionization sources, and mass analyzers have been realized. A vast array of hybrid combinations of these has resulted from specific analytical needs such as improved detection limits, precision, accuracy, elemental coverage, ease of use, throughput, and sample size. As can be seen from most of the other chapters in this volume, however, the mass analyzers used to date have primarily been magnetic sector and quadrupole mass spectrometers. Ion trapping devices, be they quadrupole ion (Paul) [1] traps or Fourier transform ion cyclotron resonance (Penning) traps, have been used quite sparingly and most work to date has concentrated on proof of principal experiments rather that actual applications. 

The tandem-in-time instruments are mostly ion-trapping devices, including ion trap and FT-ICR. They operate in a time sequence in the scan function to yield MS/MS data, mostly product ion spectra. No additional mass analyzer is required. In the case of an ion trap, the scan function begins with the isolation of ions of interest with ejection of all other ions from the ion trap, followed by (a) translational excitation of ions by applying a supplementary RF voltage to the trap and (b) mass analysis of the product ions using resonant ejection. 

A TOF mass analyser requires a pulsed ion introduction. In an electrospray-TOF combination, the duty cycle is an important issue. A significant improvement in the duty cycle can be achieved in an ion-trap-TOF hybrid instmment the ions from a continuous ion source are accumulated in the ion trap between two ion introduction events. An ion-trap-TOF hybrid instrument was first described by the group of Lubman [68-69]. The system consists of an atmospheric-pressure ion source with a vacuum interface, a set of Einzel lenses, an ion-trap device, and a reflectron time-of-flight mass analyser. The system was applied for fast analysis in combination with a variety of separation techniques [70]. 

Barinaga C. J., Eiden G. C., Alexander M. L. and Koppenaal D. W. (1996) Analytical atomic spectroscopy using ion trap devices, Fresenius J Anal Chem 355 487-493. 

Quadrupole mass filters are one of the most common and cost effective mass analyzers. Although they have limited mass resolution (Table 10.2) and are less sensitive than other mass analyzers, they are durable and suitable for high-throughput analyses. To perform a tandem mass analysis (MS/MS), a triple quadrupole MS is used in which three quadrupoles are placed in series to select, fragment, and analyze ions of interest. Quadrupole ion-trapping devices such as linear 2D ion traps are... 

Widely used in medical research, pharmaceutical and fine chemicals industries, biological and physical sciences, and security and environmental agencies, mass spectrometry techniques are continual ly under development. In Practical Aspects of Trapped Ion Mass Spectrometry Volume V, Applications of Ion Trapping Devices, an international panel of authors presents a world-wide view of the practical aspects of recent progress using trapped-ion devices. 

Part I. Ion Reactions is composed of three chapters in which ion reactions, that is, ion/neutral reactions or ion/ion reactions, are examined. Several ion-trapping devices have the capability for examining reactions of ions with neutral species and other ionic species where the extent of the reaction is monitored by the mass... 

Garrett TJ, Yost RA. The role of trapped ion mass spectrometry for imaging. In Practical Aspects of Trapped Ion Mass Spectrometry, Vol. 5, Applications of Ion Trapping Devices, March RE, Todd JFJ, Eds. CRC Press, Boca Raton, FL, 2009. 

By comparing the abundance of [BiH]+ and [B2H]+ and the corresponding dissociation rates, relative proton affinities can be estimated. In this method, protonated pseudo-dimer (e.g., the reactant ion of Equation 10.12) is produced by the ion source and stored in the ion trapping device. Because there is no ion-molecule reaction involved in this reaction, it is unnecessary to introduce gaseous basic molecules into the trapping device. The method has been used to determine the proton affinity of amino acids [75-77]. 

The orbitrap mass analyzer is an ion trap device that provides high accuracy and resolution mass measurement without the need of a magnetic field, (Hu et al. 2005 Zubarev and Makarov 2013) and thus it is more accessible in terms of lab requirements, and initial and operating costs. Some consider it to be the gold standard mass spectrometer for proteomic-based measurements (Mitchell 2010). The orbitrap mass analyzer is usually found in a hybrid configuration interfaced with a linear ion trap mass analyzer and transfer octopoles and C-trap (Fig. 2.5) (Senko et al. 2013). 

For this reason, we always rely on at least six trials or more at masses with iarge signal intensities, and at least two or three for masses with little or negligible intensity. We are examining the use of time-of-flight mass spectrometers, and an ion-trap device to obtain the entire mass spectrum at one trial. 

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