Chemical Ionization Mass Spectrometry of Nitroaromatic Vapors

The negative ion chemical ionization mass spectra nitroaromatics using a Townsend discharge ion source are reported. The chemical ionization spectra were determined in the presence of various reagent gases and at various temperatures.A sensitivity study of a chemical ionization mass spectrometry system is included which compares detection limits for nitroaromatic compounds in both positive and negative ion detection modes and provides quantitative data on the detection limits for these and other compounds. These studies illustrate the ability of negative ion chemical ionization mass spectrometry to provide two or three orders of magnitude increase in specific ion current for compounds containing electronegative functional groups. The sensitivity observed in case of nitroaromatics is useful for detection of parent ions and also permits the observation of other ions and their relationship in terms of changes in internal energy. The finding that certain organic molecules will capture low-energy electrons (i.e., less than 1 eV) to form negative ions is expected to be of general interest, since this is a very low energy form of radiation interacting and producing profound changes in organic molecules. Of the types of radiation which interact with organic molecules, low-energy electrons are perhaps the least studied. (Author)