Trace gas detection using flow reactors

Ion/molecule reaction chemistry of H₃O+ in a flow-reactor is used to detect volatile organic compounds (VOCs) emitted following wounding and drying of various crop and lawn plants. Acetaldehyde, acetone, butanone, and hexenal emissions were observed from Dutch white clover. Compound identities were confirmed using a chemical derivatization technique. The larger portion of these compounds is emitted upon drying rather than wounding and drying of crops may represent a significant source of VOCs in the troposphere. Similar emissions, although at much lower levels, seem to arise from wounding and drying of Red fescue and Kentucky bluegrass.; This same ion/molecule reaction chemistry is further employed for the detection of ethanol, acetone, diacetyl, isoprene, acetaldehyde, and butanol during the growth of the bacterium Bacillus subtilis. Compounds are quantified using an empirical calibration and the identity of isoprene was verified using gas chromatography. Other compound identities remain to be confirmed. Potential ion interferences are likely for butanol and isoprene.; Negative ion/molecule reactions are explored for their utility in on-line identification of plant wound compounds. Rate coefficients for reaction between OH− and various organic compounds were measured and reaction products were detected. Collision induced dissociation and H/D exchange reactions with isolated anions are shown to be potential tools for distinguishing isobaric ions. Emissions of HCN, acetone, and butanone are linked for a small selection of cyanogenic plants and the carbonyls are identified using H/D exchange.; The mechanism for the gas-phase reaction between hydrazinium ion (N ₂H₅+) and carbonyl compounds is investigated using both experiment and theory for its utility in selective gas-phase carbonyl detection in flow-reactors. Hydrazinium reacts to form adducts with polar organic compounds at thermal energies. Hydrazones are formed only when excess N₂H₄ is available in the reaction region. Evidence is presented that chemical and translational activation facilitate hydrazone formation.