Search

Hazardous chemical leakages involved in chemical terrorist attacks and chemical industrial accidents have been posing severe threats to human health and the environment. Vehicle-mounted mass spectrometry (MS) has been developed for continuous, on-road measurements to map the spatial and temporal distributions of hazardous chemicals. However, the detection of chemicals with small temporal scales and spatial scales is always challenging. In this study, a parallel coupling apparatus combining the techniques of ion mobility spectrometry and ion trap MS (p-IMS-ITMS) was developed to improve the detection rate and the time response capability of a stand-alone ITMS system for short time-span chemical tracking. A workflow was also proposed along with the apparatus, where the ITMS system can be triggered, as chemical suspects were discovered with the IMS system. The sampling positions of the ITMS system were investigated and optimized. In addition, a strategy was proposed to diminish the time span of samples from 1.5 to 0.5 s for evaluating the performances of the p-IMS-ITMS system. The detection rate of the stand-alone ITMS system was measured to be only 9.5, 32, and 87.5% for the time span of 0.5, 1, and 1.5 s, respectively. By comparison, the detection rates of the p-IMS-ITMS system were 99.5, 100, and 100%, where the detection rate was increased by a factor of 10 for 0.5 s time span. Moreover, the addition of an IMS system could provide temporal patterns of hazardous chemicals with a resolution of 33 ms. Finally, the potential of the p-IMS-ITMS system for environmental navigation monitoring and assessment was further demonstrated by detecting the leakages of dimethyl methyl phosphonate and dipropylene glycol monomethyl ether.

The hidden presence of fentanyl and new psychoactive substances in established illicit drugs has led to a great number of unintentional fatal overdoses, justifying the urgent need for portable tools for the rapid screening of various drugs. Ion mobility spectrometry, as a rapid detection technique, has been widely used in detecting illicit drugs, whereas it is insufficiently sensitive for bigger ions due to the mobility discrimination of an ion shutter. In this work, a miniaturized ion mobility spectrometer with an inner diameter of 14 mm and a drift length of 38.9 mm and equipped with a novel dual-compression tristate ion shutter has been developed, which could greatly reduce the mobility discrimination by compressing the ion packet twice during the injection process. The best gating performance of the dual-compression tristate ion shutter was about three times as high as that of the tristate ion shutter and twice as high as that of the Tyndall-Powell shutter. For example, the peak height was increased by 150 or 40% when the resolving power was the same, whereas the resolution of two neighboring peaks was improved by 46 or 19% when the peak heights were the same. In screening of fentanyl drug mixtures, the new shutter enhanced the identification accuracy of constituents by making peaks of slow dimer ions and complex ions observable. Besides, the new shutter helped to achieve high sensitivity for drug ions spreading a wide ion mobility range from 0.644 to 2.032 cm2 s-1 V-1, demonstrating its potential use in the analysis of other mixtures and the detection of large ions.

The application of VUV lamp-based single photon ionization (SPI) was limited due to low photon energy and poor photon flux density. In this work, we designed a quasi-trapping chemical ionization (QT-CI) source with a commercial VUV 10.6 eV krypton lamp for time-of-flight mass spectrometry. The three electrode configuration ion source with RF voltage on the second electrode constitutes a quasi-trapping region, which has two features: accelerating the photoelectrons originated from the photoelectric effect with VUV light to trigger the chemical ionization through ion-molecule reaction and increasing the collisions between reactant ion O2(+) and analyte molecules to enhance the efficiency of chemical ionization. Compared to single SPI based on VUV krypton lamp, the QT-CI ion source not only apparently improved the sensitivity (e.g., 12-118 fold enhancement were achieved for 13 molecules, including aromatic hydrocarbon, chlorinated hydrocarbon, hydrogen sulfide, etc.) but also extended the range of ionizable molecules with ionization potential (IP) higher than 10.6 eV, such as propane, dichloroethane, and trichloromethane.

Sensitive detection of black powder (BP) by stand-alone ion mobility spectrometry (IMS) is full of challenges. In conventional air-based IMS, overlap between the reactant ion O2(-)(H2O)n peak and the sulfur ion peak occurs severely; and common doping methods, providing alternative reactant ion Cl(-)(H2O)n, would hinder the formation of ionic sulfur allotropes. In this work, an ion mobility spectrometer embedded with a titration region (TR-IMS) downstream from the ionization region was developed for selective and sensitive detection of sulfur in BP with CH2Cl2 as the titration reagent. Sulfur ions were produced via reactions between sulfur molecules and O2(-)(H2O)n ions in the ionization region, and the remaining O2(-)(H2O)n ions that entered the titration region were converted to Cl(-)(H2O)n ions, which avoided the peak overlap as well as the negative effect of CH2Cl2 on sulfur ions. The limit of detection for sulfur was measured to be 5 pg. Furthermore, it was demonstrated that this TR-IMS was qualified for detecting less than 5 ng of BP and other nitro-organic explosives.

Peroxide explosives, such as triacetone triperoxide (TATP) and hexamethylene trioxide diamine (HMTD), were often used in the terrorist attacks due to their easy synthesis from readily starting materials. Therefore, an on-site detection method for TATP and HMTD is urgently needed. Herein, we developed a stand-alone dopant-assisted positive photoionization ion mobility spectrometry (DAPP-IMS) coupled with time-resolved thermal desorption introduction for rapid and sensitive detection of TATP and HMTD in complex matrices, such as white solids, soft drinks, and cosmetics. Acetone was chosen as the optimal dopant for better separation between reactant ion peaks and product ion peaks as well as higher sensitivity, and the limits of detection (LODs) of TATP and HMTD standard samples were 23.3 and 0.2 ng, respectively. Explosives on the sampling swab were thermally desorbed and carried into the ionization region dynamically within 10 s, and the maximum released concentration of TATP or HMTD could be time-resolved from the matrix interference owing to the different volatility. Furthermore, with the combination of the fast response thermal desorber (within 0.8 s) and the quick data acquisition software to DAPP-IMS, two-dimensional data related to drift time (TATP: 6.98 ms, K0 = 2.05 cm(2) V(-1) s(-1); HMTD: 9.36 ms, K0 = 1.53 cm(2) V(-1) s(-1)) and desorption time was obtained for TATP and HMTD, which is beneficial for their identification in complex matrices.

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.

Bradbury-Nielsen gate (BNG) is commonly used in ion mobility spectrometers. It, however, transmits only a small fraction of the ions into the drift region, typically 1%. In contrast, all ions in the ionization chamber could be efficiently compressed into the drift region by the field switching gate (FSG). We report in this paper on the simultaneous use of BNG and field switching (FS) to enhance ion utilization of the BNG. In this technique, the FS collects the ions existing in the region between the FS electrode and the BNG and drives them quickly, going through the BNG in the period of gate opening. The BNG acts as the retarding field in the reported FSG to stop ions from diffusing into the drift region in the period of gate closing. Using this technique, an increase of at least 10-fold in the ion peak height without any loss of resolution is achieved for acetone compared with the BNG-only approach at a gate pulse width of 150 μs, and an even larger improvement factor of 21 is achieved for heavier DMMP dimer ions. This technique can be adapted to the current BNG-based ion mobility instruments to significantly enhance their sensitivity without any modification of the drift tube hardware.

Ion mobility spectrometry (IMS) has become the most deployed technique for on-site detection of trace explosives, and the reactant ions generated in the ionization source are tightly related to the performances of IMS. Combination of multiform reactant ions would provide more information and is in favor of correct identification of explosives. Fast switchable CO3(-)(H2O)n and O2(-)(H2O)n reactant ions were realized in a dopant-assisted negative photoionization ion mobility spectrometer (DANP-IMS). The switching could be achieved in less than 2 s by simply changing the gas flow direction. Up to 88% of the total reactant ions were CO3(-)(H2O)n in the bidirectional mode, and 89% of that were O2(-)(H2O)n in the unidirectional mode. The characteristics of combination of CO3(-)(H2O)n and O2(-)(H2O)n were demonstrated by the detection of explosives, including 2,4,6-trinitrotoluene (TNT), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), ammonium nitrate fuel oil (ANFO), and black powder (BP). For TNT, RDX, and BP, product ions with different reduced mobility values (K0) were observed with CO3(-)(H2O)n and O2(-)(H2O)n, respectively, which is a benefit for the accurate identification. For ANFO, the same product ions with K0 of 2.07 cm(2) V(-1) s(-1) were generated, but improved peak-to-peak resolution as well as sensitivity were achieved with CO3(-)(H2O)n. Moreover, an improved peak-to-peak resolution was also obtained for BP with CO3(-)(H2O)n, while the better sensitivity was obtained with O2(-)(H2O)n.

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.