Ion trap method

An ionic analogy of the spin-trapping measurements are the ion-trapping methods. 2-Methyl-2-nitrosopropane also reacts with carbanions [133]... 

Many catalyst complexes that are suitable for operation and immobilization in ionic liquids are ionic themselves with the charge either located at the metal center or in the ligand sphere. Thus, these complexes are accessible to electrospray ionization mass spectroscopy (ESI-MS). However, it is not a trivial task to investigate an ionic catalyst complex next to the vast excess of ionic liquid ions. Dyson s group reported a combination of ESI-MS with quadropole ion trap methods that enabled the detection of, e.g. several cationic Rh-complexes in the ionic liquid [BMIM][PF6] [62]. They could demonstrate that the detection limit of their methodology (catalyst concentrations down to 1 x 10 mol 1 were analyzed) is so low that even complexes in the typically very low concentration of a catalytic experiment could be easily characterized, even in the presence of a large excess of ionic liquid ions. 

Ion-trap methods include Fourier transform ion cyclotron resonance MS (FTICR-MS) and quadrupole ion traps (QIT or Paul traps). In these methods, ions are produced in or transferred into a region with appropriate geometry walls and some combination of magnetic fields, DC potentials, and RF potentials that confine the ions on the timescale of seconds to days. FTICR-MS has been particularly popular for the study of organometallic ions in the gas phase. In FTICR-MS, the ions are confined by a magnetic field that constrains the ions to the center of the cell. 

Buttrill, S.E. Jr. Quadrupole Ion Trap Method Having Improved Sensitivity, US Patent 1994, 5,300,772. 

What about comparison between theory and experiment for those few systems in which lalxnatory values for or upper limits to radiative association rate coefficients are available Two systems - C " + Ho - and CH3" + H> - have been studied both by a low pressure ion trap method, in which is determined directly, and a higher pressure trap method, in which kj. is determined via extrapolation of a linear plot of k ff vs density to zero density. The results are shown in Table ni below along with theoretical phase space results derived from papers of both Herbst and Bates. The experiments utilize "normal" hydrogen, in which the cntho/para ratio is 3/1, so that the results do not pertain to the interstellar medium where H2 is thought to be in true tiiermodynamic equilibrium. In addition, care must be taken not to attempt to direct comparison with the published theoretical results on (Herbst 1982a) which utilizes sub-thermal excitation of Co-... 

The molecular constants that describe the stnicture of a molecule can be measured using many optical teclmiques described in section A3.5.1 as long as the resolution is sufficient to separate the rovibrational states [110. 111 and 112]. Absorption spectroscopy is difficult with ions in the gas phase, hence many ion species have been first studied by matrix isolation methods [113], in which the IR spectrum is observed for ions trapped witliin a frozen noble gas on a liquid-helium cooled surface. The measured frequencies may be shifted as much as 1 % from gas phase values because of the weak interaction witli the matrix. 

There are a variety of possible linked scanning methods, but only those in more frequent use are discussed here. They differ from the linked scanning methods used in triple quadrupole instruments and ion traps in that two of the three fields (V, E, and B) are scanned simultaneously and automatically under computer control. The most common methods are listed in Table 34.1, which also defines the type of scanning with regard to precursor and product ions. 

Tandem quadrupole and magnetic-sector mass spectrometers as well as FT-ICR and ion trap instruments have been employed in MS/MS experiments involving precursor/product/neutral relationships. Fragmentation can be the result of a metastable decomposition or collision-induced dissociation (CID). The purpose of this type of instrumentation is to identify, qualitatively or quantitatively, specific compounds contained in complex mixtures. This method provides high sensitivity and high specificity. The instrumentation commonly applied in GC/MS is discussed under the MS/MS Instrumentation heading, which appears earlier in this chapter. 

Electrospray ionization mass spectrometry (ESI-MS) is an analytical method for mass determination of ionized molecules. It is a commonly used method for soft ionization of peptides and proteins in quadmpole, ion-trap, or time-of-flight mass spectrometers. The ionization is performed by application of a high voltage to a stream of liquid emitted from a capillaty. The highly charged droplets are shrunk and the resulting peptide or protein ions are sampled and separated by the mass spectrometer. 

Tandem mass spectrometry (MS/MS) is a method for obtaining sequence and structural information by measurement of the mass-to-charge ratios of ionized molecules before and after dissociation reactions within a mass spectrometer which consists essentially of two mass spectrometers in tandem. In the first step, precursor ions are selected for further fragmentation by energy impact and interaction with a collision gas. The generated product ions can be analyzed by a second scan step. MS/MS measurements of peptides can be performed using electrospray or matrix-assisted laser desorption/ionization in combination with triple quadruple, ion trap, quadrupole-TOF (time-of-flight), TOF-TOF or ion cyclotron resonance MS. Tandem... 

Absorption of a light quantum leads to an electron-hole pair Eq. (19). The electron reacts with an adsorbed oxygen molecule Eq. (20), and the hole semi-oxidizes a sulfide anion at the surface Eq. (21). Further oxidation of the sulfide anion occurs by O and O2 Eq. (22). The number of Cd ions formed equals that of the sulfate anions The oxidation of illuminated CdS powders was investigated by measuring the consumption and by detecting the superoxide radical,, by an ESR spin trapping method... 

A further extension of the DFG S19 method was achieved when polar analytes and those unsuitable for GC were determined by LC/MS or more preferably by liquid chromatography/tandem mass spectrometry (LC/MS/MS). Triple-quadrupole MS/MS and ion trap MS" have become more affordable and acceptable in the recent past. These techniques provide multiple analyte methods by employing modes such as time segments, scan events or multiple injections. By improving the selectivity and sensitivity of detection after HPLC separation, the DFG S19 extraction and cleanup scheme can be applied to polar or high molecular weight analytes, and cleanup steps such as Si02 fractionation or even GPC become unnecessary. 

A multi-residue method based on SPE cleanup and gas chromatography/ion trap mass spectrometry (GC/ITMS) was developed for the determination of 120 pesticides and related metabolites in two soils with organic matter contents of 4.0-5.2%. 

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