Can Dong

Bipolar ionization source for ion mobility spectrometry based on vacuum ultraviolet radiation induced photoemission and photoionization.

A novel bipolar ionization source based on a commercial vacuum-UV Kr lamp has been developed for ion mobility spectrometry (IMS), which can work in both negative and positive ion mode. Its reactant ions formed in negative ion mode were predominantly assigned to be O(3)(-)(H(2)O)(n), which is different from that of the (63)Ni source with purified air as carrier and drift gases. The formation of O(3)(-)(H(2)O)(n) was due to the production of ozone caused by ultraviolet radiation, and the ozone concentration was measured to be about 1700 ppmv by iodometric titration method. Inorganic molecules such as SO(2), CO(2), and H(2)S can be easily detected in negative ion mode, and a linear dynamic range of 3 orders of magnitude and a limit of detection (S/N = 3) of 150 pptv were obtained for SO(2). Its performance as a negative ion source was investigated by the detection of ammonium nitrate fuel oil explosive, N-nitrobis(2-hydroxyethyl)amine dinitrate, cyclo-1,3,5-trimethylene-2,4,6-trinitramine, and pentaerythritol tetranitrate (PETN) at 150 degrees C. The limit of detection was reached at 45 pg for PETN, which was much lower than the 190 pg using (63)Ni ion mobility spectrometry under the same experimental condition. Also, its performance as an ordinary photoionization source was investigated in detecting benzene, toluene, and m-xylene.

Atmospheric pressure air direct current glow discharge ionization source for ion mobility spectrometry.

A new atmospheric pressure air direct current glow discharge (DCGD) ionization source has been developed for ion mobility spectrometry (IMS) to overcome the regularity problems associated with the conventional (63)Ni source and the instability of the negative corona discharge. Its general electrical characteristics were experimentally investigated. By equipping it to IMS, a higher sensitivity was obtained compared to that of a (63)Ni source and corona discharge, and a linear dynamic range from 20 ppb to 20 ppm was obtained for m-xylene. Primary investigations showed that alkanes, such as pentane, which are nondetectable or insensitively detectable with (63)Ni-IMS, can be efficiently detected by DCGD-IMS and the detection limit of 10 ppb can be reached. The preliminary results have shown that the new DCGD ionization source has great potential applications in IMS, such as online monitoring of environment pollutants and halogenated compounds.

Dopant-enhanced atmospheric pressure glow discharge ionization source for ion mobility spectrometry

A dopant-enhanced atmospheric pressure direct current glow discharge ionization source for ion mobility spectrometry (APDCGD-IMS) has been described. It is shown that the ion intensity can be greatly increased by addition of species with ionization energy lower than that of buffer gas when the direction of the electric field between the target electrode and the extraction electrode was opposite to that of the drift field. With N(2) as the buffer gas, adding O(2) (or air), acetone, and CH(2)Cl(2) with certain concentration can enhanced the ion intensity more than one order of magnitude, and for O(2), it was found that the enhancement depending on both the concentration of O(2) and the flow rate of the carrier gas, and the largest enhancements of the signal intensity for electron in negative mode and reaction ion in positive mode reached at O(2) concentration about 1.5%-2%. The main physicochemical processes were summarized and discussed, and a zero-dimensional reaction rate model was set up to simulate the corresponding results. It was proposed that the enhancement of signal intensity was ascribed to the various ionization processes and reactions in APDCGD.