Time Averaged Proton Magnetic Resonance Analysis of Micro Samples from Open-Tube Gas Chromatographs.

Flavor Components of Roasted Peanuts. Some Low Molecular Weight Pyrazines and Pyrrole

“…Similarly, absorptions for methylene protons which would be present in an ethyl derivative (methylene protons on carbon adjacent to pyrazine ring), and methyl protons separated from the pyrazine ring by only one methylene group, were present at 2.7 and 1.255, respectively. Standard compounds were not available to determine these chemical shifts, but NMR spectra of alkylated derivatives were obtained from Bassler and Silverstein (7) and agreement was observed in chemical shifts between the unknown spectra and those for the dimethylethylpyrazines. For example, for 2,3-dimethyl-5-ethylpyrazine, absorption due to methylene protons appeared as a quartet centered at 2.75 split by three adjacent methyl protons.…”

“…for A-methylpyrrole, methylpyrazine, and 2,5-dimethylpyrazine were obtained by analyzing commercially available chemicals of high purity on the CEC-103C mass spectrometer. However, trimethylpyrazine and isomers of methylethyl-and dimethylethylpyrazines were not commercially available, and the standard spectra in the tables for these compounds were unpublished spectra obtained from Bassler and Silverstein (7).…”

Nuclear magnetic resonance spectrometry

“…Another study of the hydrogens of NH4Cl and h'D4C1 a t atmospheric pressures finds that the change in T1 at the lambda transition is better correlated with the shear elastic constant than with expected effect of volume change on relaxation via a simple change in electrostatic potential (21 76 (1155). 7Li quadrupole splittings are observed in methyl-and ethyl-lithium (1298), in the same perdeutero compounds (1729, in Li3S (196), and in Li3N and LiNH2, but not in Liz" (870). 7Li quadrupole splittings are observed in methyl-and ethyl-lithium (1298), in the same perdeutero compounds (1729, in Li3S (196), and in Li3N and LiNH2, but not in Liz" (870).…”

“…0. 3 Micromole of hydrogen in a microcell will give a satisfactory spectrum upon time-averaging for one day (1298) ; this article describes the appropriate interfacing to a time-averaging computer and collection of the sample from an open-tube gas chromatograph. Other trigger circuits synchronize timeaveraging computers with the linear field sweep units of commercial spectrometers (751 , 276).…”

Gas chromatography

“…Other combinations of techniques useful in qualitative analysis include coupling of GC with neutron activation analysis (113), differential thermal analysis ( 463), ultraviolet spectroscopy (168), and time-average proton magnetic resonance spectroscopy (395).…”