Selectivity, chemical ionization

Hj-Lorazepam, 3-hydroxy-1,4-benzodiazepine, 45, a sedative hypnotic and antianxiety agent, has been synthesized in a seven-step procedure presented in equation 12 for use as an internal standard in GC-MS-NICI-SIM (NICl-SIM = negative ion chemical ionization-selective ion monitoring) quantitative analysis of this drug in complex matrices encountered in forensic work and for study of its complex kinetics. The procedure involved selective trideuteriation, protection of the amino group and... 

Techniques GC-MS, negative ion chemical ionization, selected ion monitoring. Reference D. L. Swackhamer, M. J. Charles, and R. A. Hites, Quantitation of toxaphene in environmental samples using negative ion chemical ionization mass spectrometry. Anal. Chem. 59 913-917 (1987). 

A Chemical Ionization Selected Ion Monitoring Assay for Methylphenidate and Ritalinic Acid... 

Brodbelt J, Liou C-C and Donovan T 1991 Selective adduct formation by dimethyl ether chemical ionization is a quadrupole ion trap mass spectrometer and a conventional ion source Ana/. Chem. 63 1205-9... 

One of the first successful techniques for selectively removing solvent from a solution without losing the dissolved solute was to add the solution dropwise to a moving continuous belt. The drops of solution on the belt were heated sufficiently to evaporate the solvent, and the residual solute on the belt was carried into a normal El (electron ionization) or Cl (chemical ionization) ion source, where it was heated more strongly so that it in turn volatilized and could be ionized. However, the moving-belt system had some mechanical problems and could be temperamental. The more recent, less-mechanical inlets such as electrospray have displaced it. The electrospray inlet should be compared with the atmospheric-pressure chemical ionization (APCI) inlet, which is described in Chapter 9. 

Table 5.2 Selected-reaction monitoring (SRM) transitions nsed for MS-MS detection of the pesticides studied in the systematic investigations on APCI-MS signal response dependence on eluent flow rate. Reprinted from J. Chro-matogr.. A, 937, Asperger, A., Efer, J., Koal, T. and Enge-wald, W., On the signal response of various pesticides in electrospray and atmospheric pressure chemical ionization depending on the flow rate of eluent applied in liquid chromatography-mass spectrometry , 65-72, Copyright (2001), with permission from Elsevier Science...

Mass Spectrometry. Mass spectrometry holds great promise for low-level toxin detection. Previous studies employed electron impact (El), desorption chemical ionization (DCI), fast atom bombardment (FAB), and cesium ion liquid secondary ion mass spectrometry (LSIMS) to generate positive or negative ion mass spectra (15-17, 21-23). Firm detection limits have yet to be reported for the brevetoxins. Preliminary results from our laboratory demonstrated that levels as low as 500 ng PbTx-2 or PbTx-3 were detected by using ammonia DCI and scans of 500-1000 amu (unpublished data). We expect significant improvement by manipulation of the DCI conditions and selected monitoring of the molecular ion or the ammonia adduction. 

By CH4-chemical ionization two predominant ions from DDS were formed in the ion source m/z 163 (M + 1) and m/z 165 (M + 3), which were accelerated and separated in the first quadrupole. Decomposition by collision activation with argon then occurred in the second quadrupole and the resulting daughter ions were separated in the third quadrupole to give rise to collision-induced spectra (equations 41-43). When carrying out the analysis with a solid inlet MS-MS system (TSQ) it was observed that, when operating TSQ in the multiple ion detection mode and selecting the ions m/z 63, 83, 85,99 and 101, only in the third quadrupole was there no interference from other m/z 163 and 165 precursor ions . ... 

Figure 9. Xenognosin B was chemically ionized (CH, 150 °C) and the (M+l)+ ion quadrapole selected and subjected to collision activation decomposition (N2) to give the mass spectrum.

Resistance to physical shocks and vibration required careful attention to selection of rugged components and to securing electrical and vacuum systems, wiring, connectors, components, and boards. Chemical ionization (Cl) was used for the first time in a fieldable military detector because of the advent of rugged turbomolecular pumps capable of handling the gas load from the Cl reagent. 

For the last several years, mass spectrometry with atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) have determined the trends in the analysis of dyes. Since 1987, various variants of ESI have been used in which droplet formation was assisted by compressed air,[1,2] temperature (e.g. Turbo Ion Spray ) or ultrasound, and they were able to handle flow rates up to 1 2 ml min This made a combination of analytical RPLC and ESI easily and widely used. The reason why it often was (and is) used instead of a traditional UV-Vis detector is the better sensitivity and selectivity of MS in comparison with spectrophotometric detection. Apart from these advantages, MS offers easily interpretable structural information. However, various... 

A rapid and simple method for PBDE and HBCD determinations in sediment and fish samples was used. The analytical method was based in selective pressurized liquid extraction (SPLE) [21] without further cleanup step and analysis by gas chromatography coupled to mass spectrometry (GC-MS), working with negative ion chemical ionization (NCI) [22, 23],... 

L6pez-Roldan P., de Alda M.J.L., and Barcelo D., 2004. Simultaneous determination of selected endocrine disrupters (pesticides, phenols and phthalates) in water by in-field solid-phase extraction (SPE) using the prototype PROFEXS followed by online SPE (PROSPEKT) and analysis by liquid chromatography-atomspheric pressure chemical ionization-mass spectrometry. Anal Bioanal Chem 378 599. 

The chemical ionization MS of a selection of substitued nitrobenzenes have been studied106. The H2 chemical ionization MS appeared significantly more useful for characterization of, e.g., isomeric compounds than the corresponding methane spectra, apparently due to the higher internal energy deposited in the protonated molecule by the reaction with H3+, and consequently in the more extensive fragmentation106. 

This review will first concentrate on the unimolecular gas-phase chemistry of diene and polyene ions, mainly cationic but also anionic species, including some of their alicyclic and triply unsaturated isomers, where appropriate. Well-established methodology, such as electron ionization (El) and chemical ionization (Cl), combined with MS/MS techniques in particular cases will be discussed, but also some special techniques which offer further potential to distinguish isomers will be mentioned. On this basis, selected examples on the bimolecular gas-phase ion chemistry of dienes and polyenes will be presented in order to illustrate the great potential of this field for further fundamental and applied research. A special section of this chapter will be devoted to shed some light on the present knowledge concerning the gas-phase derivatization of dienes and polyenes. A further section compiles some selected aspects of mass spectrometry of terpenoids and carotenoids. 

Chemical ionization (Cl) mass spectra were first obtained by using the mass-selective instability mode of the QIT. [154,155,170] The reagent gas was admitted into the QIT, ionized and then allowed to react with the analyte. 

B. Benzene as a Selective Chemical Ionization Reagent Gas. Org. Mass Spectrom. 1990, 25,497-502. 

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