Orthogonal acceleration oa-TOF

Continuous ion sources, such as ESI, can be connected to the TOF analyzers through orthogonal acceleration (oa-TOF) [205-209]. In oa-TOF, the ions generated by the source enter the TOF analyzer perpendicular to its main axis (Fig. 2.11). The acceleration potential is initially set to zero and the start pulse is generated instantaneously as the potential is raised and the ions are accelerated into the field-free flight tube. 

Quadrupole-Orthogonal Acceleration TOF Instrument As of today, quadrupole (Q)-orthogonal acceleration (oa) TOF (oa-TOF) instrument is the most popular hybrid instrument [58,59] a simphstic pictorial representation is shown in Figure 4.11. The quadrupole section consists of a normal massresolving quadrupole and an rf-only quadrupole. The latter serves as a collision cell and as an ion-accumulation device. For precursor-ion scan, the ions desired are mass-selected by the main quadrupole, accumulated in the collision cell, and a packet of the CID product ions is pushed into the TOF analyzer. The precursor-ion selection by the quadrupole is at a medium resolution, but the product-ion analysis by the TOF section is at a reasonably high resolution. 

Hieftje and co-workers first reported a design for ICP-ToF mass spectrometric systems with both orthogonal acceleration (oa) and axial acceleration (aa) geometry.39 11 The different experimental setups of ICP-ToF mass spectrometers with orthogonal and axial acceleration are compared in Figures 5.10 and 5.11. Both instruments possess a time-of-flight analyzer with a reflectron to improve the mass resolution. 

The orthogonal acceleration (oa) feature of a TOF mass analyzer enables it to be used with continuous-beam ion sources [28-31]. The ion beam from the external source enters an ion acceleration region from a direction perpendicular to the main axis of the TOF instrument (see Figure 3.13). A short pulse of an orthogonal accelerating field is applied to eject the ions efficiently in a section of... 

Figure 3 Arrangement of an oa-TOF-MS. A continuous ion beam enters from the source (top left) and sections of this beam are periodically accelerated from the orthogonal accelerator (oa) in a direction orthogonal to the beam. The packet of ions so formed is analyzed by the reflecting TOF-MS while (simultaneously) a new beam is forming in the oa.

ICP-TOF-MS with orthogonal acceleration (oa) was first introduced in 1993. A simple schematic diagram of this system is depicted in Figure 2.21. 

Orthogonal TOF is the name commonly given to what should properly be called orthogonally accelerated TOF mass spectrometry. Therefore, it is sometimes referred to by the acronym oa-TOF, especially in official publications, but it is more usual to hear it referred to simply as orthogonal TOF. 

Py/GC/MS. pyrolysis, gas chromatography, and mass spectrometry used as a combined technique Py/MS. pyrolysis and mass spectrometry used as a combined technique oa-TOF. orthogonally accelerated time of flight Q. quadrupole field or instrument... 

M. GUILHAUS [55] and A.F. DODONOV [56] describe the orthogonal acceleration time-of-flight (oa-TOF) mass spectrometer. The concept of this technique was initially proposed in 1964 by G.J. O Halloran of Bendix Corporation [57],... 

Orthogonal injection provides a high-efficiency interface for sampling ions from continuous beam to a TOF analyser. The TOF analyser allows simultaneous transmission of all ions and therefore all the ions formed are analysed. However, the duty cycle is far from 100 % for the oa-TOF spectrometer and it is lower than for the TOF spectrometer. This is due to the orthogonal accelerator that samples to the analyser only a part of the ions produced in the source. The duty cycle, despite this fact, is between 5 and 50 %. This is a considerable improvement over the conventional techniques described for coupling a continuous source to a TOF spectrometer. 

Principle of the combination of a mass spectrometer with an oa-TOF spectrometer. Ions coming from the mass spectrometer are directed to the detector. When a pulse voltage is applied to the orthogonal acceleration repeller, the ions are analysed by the TOF instrument. 

In most GC-TOF-MS instruments, an appropriate voltage pulse is applied to accelerate the ions in the direction orthogonal to their initial flight direction. In such oa-TOF-MS a nearly parallel ion beam ideally has no velocity spread, and the finite spatial spread is corrected with a linear or reflecting instrument geometry. Noise-free mass spectra are produced within a very short time (a few milliseconds). Only TOF-MS instruments have the capability required to detect peaks in GC GC since the half widths of the peaks eluting from the second column are of the order of 200 msec. Selecting the proper scan rate is essential since an increase in the acquisition speed... 

Perhaps an encouraging sign is the recent commercialization by MicroMass of a new benchtop orthogonal acceleration time-of-flight (oa-TOF) mass spectrometer that offers field ionization as an accessory. This is the first commercial FI-MS system that is not coimected to a magnetic sector instrument. Hopefully this may open up the FI-MS technique to a new generation of users. 

The ion beam is introduced perpendicularly to the TOP, and packets are accelerated orthogonally (oa-TOF) at similar frequencies, improving the sensitivity. While a packet of ions is analyzed by the reflectron, a new beam is formed in the orthogonal acceleration. 

All the data reported here were acquired on a hybrid quadrupole/ion mobility/ orthogonal acceleration time-of-flight (oa-TOF) instrument (Synapt G2 HDMS, Waters Corp., Milford, MA). A schematic of the instrument is shown in Figure 8.1. Ions generated in the atmospheric pressure source enter the vacuum system and pass through an ion guide and quadrupole mass filter to the IMS section of the instrument, which comprises three ion guides. 

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