Characterization of Chemical Weapons Convention Schedule 3 Compounds by Quantitative 13C NMR Spectroscopy

Abstract

Abstract : A quantitative 13C NMR method has been developed for characterizing hydrogen cyanide, cyanogen chloride, and phosgene, three Chemical Weapons Convention Schedule 3 compounds in common use today. Towards this end, the 13C spin-lattice relaxation behavior (T1) of the compounds has been assessed at 75 and 126 MMz for temperatures between 5-15 deg C, holding them in their liquid states to dramatically improve detection sensitivity. The derived single exponential T1 values were used to derive relaxation delays for collecting quantitative 13C data sets yielding a signal-to-noise ratio (S/N) exceeding that necessary for certifying the compounds at greater or equal 95 carbon atom % and 99% confidence. At 126 MHz, only a single data acquisition with a high-sensitivity cryogenic probe head exceeded the certifying S/N; however, for analysis at 75 MHz with a conventional probe head, greater or equal 5 acquisitions were necessary for phosgene, and greater or equal 12 acquisitions were necessary for the other two compounds. In terms of accuracy and execution time, the resulting NMR method rivals typical chromatographic methods.