Headspace Analysis of Ammonium Nitrate
Technical Report,14 Jul 2015,15 Sep 2015
Naval Research Laboratory Washington United States
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The explosive ammonium nitrate produces ammonia and nitric acid in the gaseous headspace above bulk solids, but the concentrations of the products have been observed to change with environmental conditions. Both species were detected in real time using ambient ionization mass spectrometry with custom-designed ion-molecule reaction techniques. Neither species was detected with sufficient sensitivity in real time to observe the influence of changing ambient atmospheric conditions on concentration in the headspace. Tungsten oxide, which absorbs both species and thermally desorbs NH3 and NO2, was synthesized as a bulk solid and as a thin layer coating for use as a preconcentration step. Methods used with ambient ionization were adopted and modified as necessary for conventional, low-pressure chemical ionization mass spectrometry to detect pre-concentrated analyte samples in the absence of background interference. Ammonia was detected successfully, but the pre-concentrator reduced nitric acid to compounds smaller than NO2, including N2, that could not be detected apart from background. The methodology to accurately measure ammonia and nitric acid above bulk ammonium nitrate was resolved but lacked a sufficiently-developed tungsten oxide pre-concentrator.
- Inorganic Chemistry