Search

Membrane-extraction ion mobility spectrometry (ME-IMS) has been developed for in situ sampling and analysis of trace chlorinated hydrocarbons in water in a single procedure. The sampling is configured so that aqueous contaminants permeate through a spiral hollow poly(dimethylsiloxane) (PDMS) membrane and are carded away by a vapor flow through the membrane tube. The extracted analyte flows into an atmospheric-pressure chemical-ionization (APCI) chamber and is analyzed in a specially made IMS analyzer. The PDMS membrane was found to effectively extract chlorinated hydrocarbon solvents from the liquid phase to vapor. The specialized IMS analyzer has measured resolutions of R = 33 and 41, respectively, for negative-and positive-modes and is capable of detecting aqueous tetrachloroethylene (PCE) and trichloroethylene (ICE) as low as 80 and 74 [micro]g/L in the negative ion mode, respectively. The time-dependent characteristics of sampling and detection of TCE are both experimentally and theoretically studied for various concentrations, membrane lengths, and flow rates. These characteristics demonstrate that membrane-extraction IMS is feasible for the continuous monitoring of chlorinated hydrocarbons in water. 10.1021/ac100162d

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 [sup.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 [sup.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 [sup.36]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.

Direct mass spectrometric measurements of saturated hydrocarbons, especially small n-alkanes, remains a great challenge because of low basicity and lack of ionizable functional groups. In this work, a novel high-pressure photoelectron-induced O 2 + cation chemical ionization source (HPPI-OCI) at kPa based on a 10.6 eV krypton lamp was developed for a time-of-flight mass spectrometer (TOFMS). High-intensity O 2 + reactant ions were generated by photoelectron ionization of air molecules in the double electric field ionization region. The quasi-molecular ions, [M-H] + , of C3-C6 n-alkanes, gradually dominated in the mass spectra when the ion source pressure was elevated from 88 to 1080 Pa, with more than 3 orders of magnitude improvement in signal intensity. As a result, the achieved limits of detection were lowered to 0.14, 0.11, 0.07, and 0.1 ppbv for propane, n-butane, n-pentane, and n-hexane, respectively. The performance of the HPPI-OCI TOFMS was first demonstrated by analysis of exhaled small n-alkanes from healthy smokers and nonsmokers. Then the concentration variations of exhaled small n-alkanes of four healthy volunteers were analyzed after alcohol consumption to explore the alcohol-hepatoxicity-related oxidative stress. In summary, this work provides new insights for controlling the O 2 + -participating chemical ionization by adjusting the ion source pressure and develops a novel direct mass spectrometric method for sensitive measurements of mall n-alkanes.

Ion mobility spectrometry (IMS) is a key trace detection technique for explosives and the development of a simple, stable, and efficient nonradioactive ionization source is highly demanded. A dopant-assisted negative photoionization (DANP) source has been developed for IMS, which uses a commercial VUV krypton lamp to ionize acetone as the source of electrons to produce negative reactant ions in air. With 20 ppm of acetone as the dopant, a stable current of reactant ions of 1.35 nA was achieved. The reactant ions were identified to be CO(3)(-)(H(2)O)(n) (K(0) = 2.44 cm(2) V(-1) s(-1)) by atmospheric pressure time-of-flight mass spectrometry, while the reactant ions in (63)Ni source were O(2)(-)(H(2)O)(n) (K(0) = 2.30 cm(2) V(-1) s(-1)). Finally, its capabilities for detection of common explosives including ammonium nitrate fuel oil (ANFO), 2,4,6-trinitrotoluene (TNT), N-nitrobis(2-hydroxyethyl)amine dinitrate (DINA), and pentaerythritol tetranitrate (PETN) were evaluated, and the limits of detection of 10 pg (ANFO), 80 pg (TNT), and 100 pg (DINA) with a linear range of 2 orders of magnitude were achieved. The time-of-flight mass spectra obtained with use of DANP source clearly indicated that PETN and DINA can be directly ionized by the ion-association reaction of CO(3)(-) to form PETN·CO(3)(-) and DINA·CO(3)(-) adduct ions, which result in good sensitivity for the DANP source. The excellent stability, good sensitivity, and especially the better separation between the reactant and product ion peaks make the DANP a potential nonradioactive ionization source for IMS.