Mass analyzer ideal

MALDI generated a great demand for a mass analyzer ideally suited to be used in conjunction with a pulsed ion source and capable of transmitting ions of extremely high mass up to several 10 u. [24] Since then, the performance of TOF instruments has tremendously increased. [25,26] TOF analyzers were adapted for use with other ionization methods and are now even strong competitors to the well-established magnetic sector instruments in many applications. [25,27]... 

Ionization methods in mass spectrometry are divided into gasphase ionization techniques and methods that form ions from the condensed phase, either inside or outside of the MS. All ion sources are desired to produce ions without mass discrimination from the sample and to transport them into the mass analyzer. Ideally, ions should be produced with high efficiency (ion yield) and transported to the mass analyzer with no loss (high transport efficiency). 

In the past decade, as systems have become simpler to operate, mass spectrometry (MS) has become increasingly popular as a detector for GC. Of all detectors for GC, mass spectrometry, often termed mass selective detector (MSD) in bench-top systems, offers the most versatile combination of sensitivity and selectivity. The fundamentals of MS are discussed elsewhere in this text. Quadrupole (and ion trap, which is a variant of quadrupole) mass analyzers, with electron impact ionization are by far (over 95%) the most commonly used with GC. They offer the benefits of simplicity, small size, rapid scanning of the entire mass range and sensitivity that make an ideal detector for GC. 

The properties of an ideal mass analyzer are well described, [2] but despite the tremendous improvements made, still no mass analyzer is perfect. To reach a deeper insight into the evolution of mass spectrometers the articles by Beynon, [3] Habfast and Aulinger, [4,5] Brunnee [6,7], Chapman et al. [8] and McLuckey [9] are recommended for further reading. In recent years, miniature mass analyzers have gained interest for in situ analysis, [10] e.g., in environmental [11] or biochemical applications, [12] for process monitoring, for detection of chemical warfare agents, for extraterrestrial applications, [13] and to improve Space Shuttle safety prior to launch. [14]... 

Brunnee, C. The Ideal Mass Analyzer Fact or Fiction Int. J. Mass Spectrom. lonProc. 1987, 76, 125-237. 

Laser desorption intrinsically is a pulsed ionization process, which is therefore ideally combined with time-of-flight (TOF) analyzers (Chap. 4.2). [16,49] Ever since the first MALDI experiments, MALDI and TOF have been forming a unit, and the majority of MALDI applications are MALDI-TOF measurements. Vice versa, it was the success of MALDI that pushed forth the tremendous delevopment of TOF mass analyzers. More recently, MALDI has also been adapted to orthogonal acceleration TOF analyzers. [147]... 

Hybrid Mass Spectrometer A tandem mass spectrometer comprised of multiple mass analyzers of different types. A Q-TOF is a hybrid, but a triple quadmpole is not. Ideally, a hybrid instrument harnesses the best features of each mass analyzer type to produce a system perhaps greater than the sum of the parts. 

C. Brunnee, The ideal mass analyzer fact or fiction , Int. J. Mass Spectrom. Ion Proc., 76(1987) 125. 

ToF analyzers are relatively small and of medium expense and so represent a good alternative to magnetic sector and ( analyzers, especially when their speed and sensitivity advantages are considered. Their mass accuracy and ease of calibration are also well established. ToF analyzers also have the highest practical mass range of all mass analyzers. However, the digitizer speed may place limitations on the instrumental dynamic range. The very fast acquisition rates that are achieved in ToF analyzers mean that they are also ideally suited... 

Postsource reactions are governed by a number of factors such as the internal energy of the ions, the time between exit of ions from the source to mass analysis, and the pressure of the mass analyzer. Since there is no ideal mass analyzer [2], a range of analyzers are commercially available which have been interfaced with most of the common ionization methods. Each mass analyzer has unique properties which can influence the actual mass spectrum observed. 

Quadrupole mass analyzers consist of four parallel metal rods which are either round-shaped or ideally have a hyperbolic section. Ion separation is realized by applying an alternating electrical fleld to the four rods with each pair of adjacent rods having the opposite signs of the potential. The potential applied to two opposite rods is a superposition of a constant potential U and an alternating potential V cos mt (Eq. (5.1)). The other two opposite rods bear the potential . co describes the angular frequency and equals Inv when v is the frequency of the applied radio frequency field t is the time. 

By examining this brief history of the development of instrumentation and methods, it should be clear what parameters define the instrument of choice for analysis of pharmaceutically important molecules. Such an instrument is one capable of performing LC-MS, typically using a reverse-phase HPLC separation and one of the API techniques. MS-MS capability is desirable—using an ion trap, a triple quadrupole, or other tandem mass analyzer instrument. Accurate mass measurement capability is also desirable. These attributes make up a prioritized list of capabilities for the ideal full-purpose instrument to be used in a pharmaceutical research environment. As one progresses through this list, the expense of the instrument increases, the sophistication of the instrument increases, and the intellectual and technological commitment required to do these experiments increases. 

Matrix effects can be important during the analysis of petroleum products. They generally disturb intensities emitted by a detected isotope [10]. Organic matrix may modify element ionization in the plasma and consequently cause a variation of sensitivity. For these reasons, a standard addition method was performed for the calibration procedure to control the matrix effects. Concentrations of metals in analyzed organic samples must be compatible with ICP-MS potential in order to obtain reliable results. Experience shows that concentrations detected by the mass spectrometer ideally should be in the range of 1-100 ng/g. Thus, for optimal detection conditions, samples were diluted in xylene according to their pre-estimated element concentration range. 

Figure 16.9. Quadrupole mass-analyzer. Ions are injected from the electron-impact source along the z-axis. Ideally, the poles are hyperbolic in cross-section in practice, circular poles are used. Pole length is approximately 20 cm and r about 1 cm.

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