CHLORINE ISOTOPIC RATIOS BY NEGATIVE ION MASS SPECTROMETRY

For kinetic isotope effect studies the determination of the relative isotopic abundances of chlorine-35 and chlorine-37 can be accomplished directly on gaseous methyl chloride samples by comparison of the Cl- ion intensities with a conventional isotope-ratio mass spectrometer equipped for negative ion operation. Procedures for the conversion of inorganic chloride samples to gaseous methyl chloride were examined to ensure isotopic identity of the methyl chloride from the chloride precursor. Because relative rather than absolute abundances are required for this application, rapid switching between sample and standard is used to compensate for instrument drift and background. A comparison between positive and negative ion ratios revealed several advantages to be gained by the negative ion technique. © 1969, American Chemical Society. All rights reserved.