Mode selective reaction

B2.5.5.4 LASER ISOTOPE SEPARATION AND MODE-SELECTIVE REACTIONS... 

Nishiyama et al. (2004) set out to quantitate DHT in human serum and prostate biopsy tissue using LC-MS with charged derivatization to the A-methylpyridinium derivative. Prostate tissue DHT was dissolved in alkaline solution, extracted by SPE and derivatized before LC-MS analysis [ESI, positive ion mode, selected reaction monitoring (SRM)]. Pretreatment values in patients with N = 69) or without N = 34) prostate cancer were, for serum DHT, 423.9 pg mL ( 1.46 nmol L ) with SD 243.2 pg mL (< 0.84 nmol L ) or... 

ABSTRACT. Potential energy surfaces (PESs) of several elementary chemical reactions are investigated by ab initio calculations. Topics included are (1 spectroscopy during the K + NaCl and Na + KCl reactions, (2) f + CO charge transfer reaction, (3) photodissociation and (4) two examples of mode-selective reactions. In connection to recent experiments on each subject,... 

MS settings El mode/EI mode/selective reaction monitoring/ nonresonant collision induced mode... 

Quack M 1991 Mode selective vibrational redistribution and unimolecular reactions during and after IR-laser excitation Mode Selective Chemistry ed J Jortner, R D Levine and B Pullman (Dordrecht Kluwer) pp 47-65... 

The most common modes of operation for ms/ms systems include daughter scan, parent ion scan, neutral loss scan, and selected reaction monitoring. The mode chosen depends on the information required. Stmctural identification is generally obtained using daughter or parent ion scan. The mass analyzers commonly used in tandem systems include quadmpole, magnetic-sector, electric-sector, time-of-flight, and ion cyclotron resonance. Some instmments add a third analyzer such as the triple quadmpole ms (27). 

Therefore, in order to obtain a 1,4-addition of an allyl residue to an enone, two activation modes can be used reactions take place either under electrophilic conditions with Lewis acid promotion, or in the presence of fluoride ions. This is important as the stereochemical outcome often depends on the activation mode selected. 

The lone pairs on the nitrogen and oxygen atoms make a significant difference in the chemical reactions (Scheme 17). P-Arylenamines undergo [2-t-2] cycloaddition reactions [93] whereas P-arylenol ethers undergo [2h-2h-2] cycloaddition reactions [94]. The mode selectivity was attributed [95] to the HOMO amplitude or the n bond polarity. 

The instrument scan mode called selected reaction monitoring (SRM) is generally used for quantitative applications. SRM is similar to selected ion monitoring (SIM) in single quadrupole MS. The difference is that a product ion from the decomposition reaction in the collision cell is measured instead of a single ion formed in the... 

Plant material is homogenized in acetone followed by addition of water. The filtered extract is diluted with acetone-water (2 1 v/v) and filtered through a syringe filter. The sample extract is diluted 1 1 with a deuterated azinphos-methyl internal standard and analyzed using LC/MS/MS in the positive-ion selected reaction monitoring (-I-SRM) mode. 

Water samples, received from the respective groundwater trials, are analyzed by direct aqueous injection (DAI) by LC/ESI-MS/MS. A 1-mL volume of the water is pipetted into a 1.8-mL autosampler vial. The internal standard solution is added (200 qL) and mixed. The vials are capped and analyzed by LC/ESI-MS/MS using the selected reaction monitoring (SRM) mode. 

Fig. 11 Mode-selective ESPT in 2-(2 -Pyridyl)pyrrole indicates that the ESIPT reaction is associated with in-plane vibration modes (reprint from ref. [97], Copyright 2005 American Chemical Society)...

Sinha, A. Hsiao, M. C., and Crim, F. F. (1991), Controlling Bimolecular Reactions Mode and Bond Selected Reaction of Water with Hydrogen Atoms, J. Chem. Phys. 94, 4928. 

LC/MS/MS with selected reaction monitoring and ESI in the negative-ion mode was used to detect RDX and its degradation products in contaminated groundwater [18]. The detected degradation products were MNX (hexahydro-l-nitroso-3,5-dinitro-l,3,5-triazine), DNX (hexahydro-l,3-dinitroso-5-nitro-l,3,5-triazine) and TNX (hexahydro-l,3,5-trinitroso-l,3,5-triazine). The [M + 75] and [M + 45] were the most intense ions in the mass spectra of RDX and its degradation products. In the CID mass spectra, the base peak for RDX, MNX and DNX... 

The use of MALDI for the analysis of small molecules was recently reported. Particularly attractive is the coupling of a MALDI source with a triple quadrupole mass analyzer for quantitative analysis in the selected reaction monitoring (SRM) mode due to very high analysis speed. 

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