Characteristic ion /molecule reactions at low and at atmospheric pressure for selective detection of dangerous substances
Characteristic ion/molecule reactions are selective to substrates with a specific functionality and therefore are useful in enhancing the selectivity in the detection of trace organic compounds when coupled with mass spectrometry. Nitroaromatic compounds can be reduced to arylnitrenium ions by vinyl halide radical cations and can form σ-bonded Meisenheimer complexes with carbon/oxygen-centered anions in the gas phase due to their strong electron deficiency. Also, phosphonium ions were found to undergo selective ketalization with 1,4-dioxane. It has been demonstrated that explosives and chemical warfare agent simulants in mixtures can be selectively detected using these new characteristic ion/molecule reactions. Another characteristic ion/molecule reaction uncovered is the cycloaddition/cyclization of the TNT and RDX fragment ions with ethyl vinyl ether. A thermal desorption-APCI method was also developed for the detection of explosives on solid surfaces, in which explosives were desorbed from the surface by rapid heating and then underwent ionization or ion/molecule reactions. In addition, a new atmospheric pressure thermal desorption ionization (APTDI) method was established for producing ions from organic ionic compounds by heating at atmospheric pressure. The effect of matrix and solvent on the ionization was examined. While the ion/molecule reactions mentioned above were performed at low pressure inside the mass spectrometer, several ion/molecule reactions, such as Meisenheimer complexation, ketalization, conversion of pyrylium into pyridinium ion, Eberlin and deprotonation reactions, were also investigated in the gas phase at atmospheric pressure by employing ESI, APCI and APTDI with designed reactors. Finally, stereoselective proton transfer reactions were successfully used for chiral recognition using tandem mass spectrometry. The hydrogen/chlorine exchange reaction between carbanion CH2NO2- and CCl4 is also studied.
Cooks, Purdue University.
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