Detection mass-selected

Ions can be collected very efficiently and detected mass-selectively. The method of choice for the production of ions for analytical purposes is the species-selective multiphoton ionization, with lasers in the visible or the UV. When used for identifying the absorbing species the method is implemented via a resonance-enhanced route as discussed below. But using very high laser powers, it is possible to ionize in an indiscriminate (or not resonant) fashion any species that is present in the path of the laser beam. In dynamics, mnltiphoton ionization is used to probe reaction products as noted in Sections 7.1.2.1 and 7.1.2.4 and in specific examples. 

In TOF-SARS [9], a low-keV, monoenergetic, mass-selected, pulsed noble gas ion beam is focused onto a sample surface. The velocity distributions of scattered and recoiled particles are measured by standard TOF methods. A chaimel electron multiplier is used to detect fast (>800 eV) neutrals and ions. This type of detector has a small acceptance solid angle. A fixed angle is used between the pulsed ion beam and detector directions with respect to the sample as shown in figure Bl.23.4. The sample has to be rotated to measure ion scattering... 

The influence of soil ageing on the recovery of POPs from spiked soil samples was also assessed. Spiked lettuce samples were subjected to in vitro gastrointestinal extraction to assess the bioavailability of Endosulfan compounds. All samples (soil and lettuce) were extracted using pressurised fluid extraction and analysed using gas chromatography with mass selective detection. 

Figure 2.12 Schematic representation of an on-line SPE-GC system consisting of three switching valves (VI-V3), two pumps (a solvent-delivery unit (SDU) pump and a syringe pump) and a GC system equipped with a solvent-vapour exit (SVE), an MS instrument detector, a retention gap, a retaining precolumn and an analytical column. Reprinted from Journal of Chromatography, AIIS, A. J. H. Eouter et al, Analysis of microcontaminants in aqueous samples hy fully automated on-line solid-phase extraction-gas chromatography-mass selective detection , pp. 67-83, copyright 1996, with permission from Elsevier Science.

A. J. H. Louter, C. A. van Beekvelt, P Cid Montanes, J, Slobodnik, J. J. Vreuls and U. A. Th Brinkman, Analysis of microcontaminants in aqueous samples by fully automated on-line solid-phase exti action-gas cliromatography-mass selective detection , 7. Chromatogrl2S 67-83 (1996). 

Stan H-J. 1989. Application of capillary gas chromatography with mass selective detection to pesticide residue analysis. J Chromatogr 467 85-98. 

Leung AM, McDonough DM, West CD. 1998. Determination of endosulfans in soil/sediment samples from Point Mugu, Oxnard, CA, using capillary gas chromatography/mass selective detection (CC/MSD). Environmental Monitoring and Assessment 50(l) 85-94. 

We use laser photofragment spectroscopy to study the vibrational and electronic spectroscopy of ions. Our photofragment spectrometer is shown schematically in Eig. 2. Ions are formed by laser ablation of a metal rod, followed by ion molecule reactions, cool in a supersonic expansion and are accelerated into a dual TOE mass spectrometer. When they reach the reflectron, the mass-selected ions of interest are irradiated using one or more lasers operating in the infrared (IR), visible, or UV. Ions that absorb light can photodissociate, producing fragment ions that are mass analyzed and detected. Each of these steps will be discussed in more detail below, with particular emphasis on the ions of interest. 

P 24] The nitration of naphthalene was carried out with dissolved or in situ generated N2O5 gas [37]. The temperatare was set to -10 to 50 °C and residence times to 15—45 s. The reaction mixtare processed in the micro reactor was quenched with water, extracted and analyzed by HPLC or GC with mass-selective detection. 

A survey of the literature with a key phrase tissue residue analysis yielded a distribution of separation and detection techniques as outlined in Table 2. LC with either UV or fluorescence detection was the most common separation and detection technique, representing 61% of the citations. The results are an indication of the maturity of LC as a common, well-understood technique. The second most commonly used technique cited in the literature (13%) was GC with either a mass-selective or electron capture detector. GC is also a mature technology and a good choice owing to the... 

Chromatographic systems were finally coupled with relatively inexpensive, yet powerful, detection systems with the advent of the quadrupole mass selective detector (MSD). The operational complexity of this type of instrumentation has significantly declined over the last 15 years, thus allowing routine laboratory use. These instruments... 

Gas chromatography with electron capture and/or mass-selective detection... 

Visible wavelength spectrophotometry Mass selective detection Nitrogen-phosphorus detection Electron capture detection UV detection... 

Specificity is unsurpassed. Traditionally, MS was performed on very large and expensive high-resolution sector instruments operated by experienced specialists. The introduction of low-resolution (1 amu), low-cost, bench-top mass spectrometers in the early 1980s provided analysts with a robust analytical tool with a more universal range of application. Two types of bench-top mass spectrometers have predominated the quadrupole or mass-selective detector (MSD) and the ion-trap detector (ITD). These instruments do not have to be operated by specialists and can be utilized routinely by residue analysts after limited training. The MSD is normally operated in the SIM mode to increase detection sensitivity, whereas the ITD is more suited to operate in the full-scan mode, as little or no increase in sensitivity is gained by using SIM. Both MSDs and ITDs are widely used in many laboratories for pesticide residue analyses, and the preferred choice of instrument can only be made after assessment of the performance for a particular application. 

MSD provides molecular weight, fragmentation information and mass selectivity. Also, simultaneous GC-MS/MIP-AES has been described, using both a low-pressure and an atmospheric-pressure splitter [336]. The combination of MS and AED data sets provides the potential for application to a wide range of analytical problems, such as screening for the presence of hetero-atom-containing analytes (AED), identification and confirmation (MS) and quantification (MS, AED). On-line LVI-GC-AED/MS (dual detection) has been described with small (i.e. less than 0.5 s) differences in retention time of a compound with AED and MS detection [67], The dual-hyphenation set-up largely eliminates data-interpretation problems caused by small differences in retention time, or retention indices and is,... 

If we consider only a few of the general requirements for the ideal polymer/additive analysis techniques (e.g. no matrix interferences, quantitative), then it is obvious that the choice is much restricted. Elements of the ideal method might include LD and MS, with reference to CRMs. Laser desorption and REMPI-MS are moving closest to direct selective sampling tandem mass spectrometry is supreme in identification. Direct-probe MS may yield accurate masses and concentrations of the components contained in the polymeric material. Selective sample preparation, efficient separation, selective detection, mass spectrometry and chemometric deconvolution techniques are complementary rather than competitive techniques. For elemental analysis, LA-ICP-ToFMS scores high. 

Undoubtedly, the technique most suited to tackle polyatomic multichannel reactions is the crossed molecular beam (CMB) scattering technique with mass spectrometric detection and time-of-flight (TOF) analysis. This technique, based on universal electron-impact (El) ionization coupled with a quadrupole mass filter for mass selection, has been central in the investigation of the dynamics of bimolecular reactions during the past 35 years.1,9-11 El ionization affords, in principle, a universal detection method for all possible reaction products of even a complex reaction exhibiting multiple reaction pathways. Although the technique is not usually able to provide state-resolved information, especially on a polyatomic... 

Leenheers, L.H., Breugel, D.G., Ravensberg, J.C., Meuling, W.J.A., and Jongen, M.J.M. (1992) Determination of 2-isopropoxyphenol in urine using capillary gas chromatography and mass-selective detection, ]. Chromatography, 578 189-194. 

The precursor ion is mass-selected with Q and subjected to single-collision conditions, collision gases Ar or Xe, in the AC only quadrupole Q2. The CID-pro-duced ions are detected with Q3 (not shown in Figure 9). For additional details see experimental parts of papers.63-64... 

In order to measure cross sections, a beam of electrons of known energy is directed through a gas sample of known pressure and the resulting ion and electron currents measured.63 If mass selective ion detection is used, then partial ionization cross sections oz may be determined. These cross sections correspond to the production of z electrons and an ion or ions having total charge +ze. Some instruments allow the counting cross section oc, also known as the ion production cross section, to be determined ... 

A number of other laser spectroscopic techniques are of interest but space does not permit their discussion. A few specialized methods of detecting laser absorption worthy of mention include multiphoton ionization/mass spectrometry (28), which is extremely sensitive as well as mass selective for gas-phase systems optically detected magnetic resonance (29) laser intracavity absorption, which can be extremely sensitive and is applicable to gases or solutions (30) thermal blooming, which is also applicable to very weak absorbances in gases or liquids (31) and... 

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