[Discharge ion mobility spectrometry of ketonic organic compounds]

Ion mobility spectrometry (IMS) is a sensitive technique for fast on-line monitoring trace volatile organic compounds based upon the mobilities of gas phase ions at ambient pressure in weak electric field. In the present work, protonated water reactant ions were successfully prepared, and eight ketones were studied on a homemade high-resolution IMS apparatus using a discharge ionization source. The reduced mobility values of all ions were derived from the observed ion mobility spectra. The experimentally determined reduced mobilities for acetone, 2-butone, 1-methyl-2-pyrrolidinone acetophenone, cyclohexanone and product ions were compared with the previously reported values in the Ni-IMS, indicating that they are in good agreement. The reduced mobilities of methyl isopropyl ketone, 4-methyl-2-pentanone and cyclopentanone ions were given for the first time. The ionization process for organic compounds in the authors' discharge ion mobility spectrometer is suggested to be similar to Ni-IMS system, i.e., the proton transfer reactions produce protonated ketone ions. In addition, a linear correlation was found between the reduced mobilities of the ketone ions and their molecular masses. Qualitative measurements show that the limit of detection is in the ng x L(-1) order of magnitude in the authors' discharge ion mobility spectrometer.