Isomer differentiation

Zhang, J. and Brodbelt, J.S., Structural characterization and isomer differentiation of chalcones by electrospray ionization tandem mass spectrometry, J. Mass Spectrom., 38, 555, 2003. 

We would like to thank Jim Scrivens of ICI, Ltd. for the epoxy resin extract and guidance on the use of CAD for isomer differentiation in the mixture. 

ISome Differentiating Features of Ionic Liquids (Pure Liquid Electrolytes)... 

The inherent analytical advantages of MS/MS experiments are enhanced specificity and improved signal-to-noise ratio. It is useful in isomer differentiation, protein sequencing, and mixture analysis. MS/MS experiments are often performed in combination with HPLC for analysis of complex mixtures. 

Gurka, D.F. Billets, S. Brasch, J.W. Riggle, C.J. Tetra-chlorodibenzodioxin isomer differentiation by micro diffuse reflectance fourier transform infrared spectrometry at the low nanogram level. Anal. Chem. 1985, 57, 1975-1979. 

Simonsick WJJ, Hites RA. 1985. Charge exchange chemical ionization mass spectrometry A tool for PAH isomer differentiation. In Cooke M, Dennis AJ, eds. Polynuclear aromatic hydrocarbons Mechanisms, methods and metabolism. Columbus, OH Battelle Press, 1227-1237. 

The fluorescence of the ortho-aminobenzoate motif was utilized to elaborate a continuous fluorimetric assay based on intramolecular fluorescence quenching through isomer-differential collision of the fluorophore and a quencher, i.e. nitro-phenylalanine or a para-nitrophenyl moiety at the C-terminus [57]. Relative fluorescence recorded at 410 nm (2ex = 317 nm) is cleared from the participation of the preexisting trans isomer, but this assay is limited to peptides bearing fluoro-phores and properly positioned fluorescence quencher moieties. 

Chemical Ionization (Cl) is a soft ionization technique that produces molecular ions (M" " or M ), adduct ions (M CI reagent), and fragment ions. Instrumentation is more expensive but Cl permits isomer differentiation. Cl reagents are usually methane, isobutane, or ammonia. The degree of fragmentation is less than in EL... 

SFC-APCI-MS using methanol-water-modified carbon dioxide as the mobile phase has been applied to the analysis of PACs. A direct fluid introduction interface with flow splitting removed two thirds of the SEC effluent transferred to the APCI-MS system. PACs were separated on a Cjg packed column at 45°C and LCDs were similar to those obtained with HPLC-UV. SFC-APCI-MS-MS using microbore packed columns applied to the analysis of PACs in coal tar was able to provide structural information for isomer differentiation. LODs in the low ng range were obtained by SIM. 

R. J. Leibrand, The Power of the IRD Isomer Differentiation, Hewlett-Packard application note IRD88-7, 1988. 

We recommend that initially all tandem MS experiments be carried out using the identical collision energy. Best results for isomer differentiation across all isomers should, at least in theory, be achieved if the isomer with the lowest 50 value is fragmenting and 100% collision energy with this optimized value is applied across all isomers. 

Research in the area of small molecule gas-phase H/D exchange in ion traps has focused primarily on two fronts (1) model systems to investigate the mechanisms of H/D exchange and (2) isomer differentiation. 

Because of the differences in biological activity of PAC isomers, the analytical challenge is to identify and quantify all of the PACs in a particular environment. The task of isomer differentiation is particularly difficult because of the large number of possible isomeric PACs, e.g., the number of possible isomers of unalkylated condensed four-ring PAHs is three, benzo(a) anthracene, chrysene, and triphenylene, whereas of unalkylated mononitrobenzo(a)anthracene is 12. 

Williams, E.R. and McLafferty, F.W. (1990) 193-nm laser photoionization and photodissociation for isomer differentiation in Fourier-transform mass-spectrometry. J. Am. Soc. Mass Spectrom., 1, 361-365. 

Aromatics [benzene, toluene, and xylene (BTX)] are obtained from refinery and petrochemical light naphtha streams. Aromatics are produced in the reforming process and in steam cracking. Extraction or various extractive distillation processes are used to isolate and separate aromatics from the naphtha streams. Typical extraction processes are based on tetraethylene glycol, sulfolane, N,N -methylpyrolidene, or morpholine. They produce a mixture of aromatics that are subsequently separated by distillation, extractive distillation, or—in the case of xylene isomers—differential adsorption or fractional crystallization. 

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