离子迁移谱定量检测复杂基质中新型炸药六亚甲基三过氧化二胺

六亚甲基三过氧化二胺( Hexamethylene triperoxide diamine, HMTD)是一种新型有机过氧化爆炸物,由于原料易得、制备方法简单,常被用于恐怖袭击和犯罪活动中。本实验基于非放射性电离源真空紫外灯( VUV)发展了一种试剂分子辅助灯电离正离子迁移谱技术,通过优化筛选试剂分子,最终选择丙酮作为HMTD定量检测的试剂分子。利用质谱对丙酮的反应试剂离子和HMTD的产物离子进行了离子归属,确定反应试剂离子为丙酮二聚体离子 m/z 117[( CH3)2 CO ]2 H+, HMTD 的产物离子为其质子化的分子离子m/z 209[ HMTD+H]+。在迁移管和热解析温度120℃的条件下,利用HMTD最大信号强度和第10 s的信号强度对其标准样品进行定量检测,线性范围分别为5~50 ng/μL和5~100 ng/μL,检出限分别可达0.2和0.3 ng/μL。化妆品如香水等常常干扰和抑制离子迁移谱测量,发展在香水基质中HMTD的现场快速筛查和检测方法具有现实意义。将这两种定量方法应用于3种不同品牌香水样品中HMTD的定量检测,对比发现利用HMTD第10 s的信号强度进行定量具有较好的回收率和准确性,该方法适用于复杂基质中HMTD的准确快速定量检测。     

Quantitative determination of n-alkanethiols in air and in a blended gas mixture of methane with air by gas chromatography/differential mobility spectrometry

Mixtures of n-alkanethiols, in solution with equi-molar amounts from 0.5 to 360 ng per compound, were determined using gas chromatography (GC) with a differential mobility spectrometer, operated with a flow of air at ambient pressure, as the GC detector. A homologous series of n-alkanethiols with carbon number from two to six showed baseline resolution in the GC separation and positive and negative ion chromatograms were produced simultaneously for the alkanethiols. Differential mobility spectra showed compensation voltages characteristic of each alkanethiol and plots of ion intensity, retention time, and compensation voltage yield contour plots illustrating the second dimension of analytical selectivity provided by the detector. Another yet undeveloped dimension of analytical information was found in the dependence of mobility coefficients on electric field. Mass-analysis of ions from thiols showed a hydrogen abstracted ion, protonated monomers, and proton bound dimers. Linear ranges were narrow and the minimum detectable limits were ~1 ng. Response in positive polarity provided a ten-fold improvement in detection limits though spectra were more complex than for negative ions. In a methane-rich air atmosphere, intended to simulate ambient air or the detection of leaks from natural gas pipelines, the response to thiols with negative ions was not degraded by the methane up to 50% v/v, the highest level tested.     

Electron capture ion mobility spectrometry for the selective detection of chlorinated and brominated species after capillary gas chromatography

This paper reports the first investigation of electron capture ion mobility spectrometry as a detection method for capillary gas chromatography. In previous work with negative ion mobility detection after gas chromatography, the principal reactant ion species were O₂^? or hydrated O₂^? due to the presence of oxygen in the drift gas. These molecular reactant ions have a mobility similar to chloride and bromide ions, which are the principal product ions formed by most halogenated organics via dissociative ion-molecule reactions. Oxygenated reactant ions thus interfere with the selective detection of chloride and bromide product ions. A recently described ion mobility detector design efficiently eliminated ambient impurities, including oxygen, from infiltrating the ionization region of the detector; consequently, in the negative mode of operation, the ionization species with N₂ drift gas were thermalized electrons. Thermalized electrons have a high mobility and their drift time occupies a region of the ion mobility spectrum not occupied by chloride, bromide, or other product ions. The result was improved selectivity for halogenated organics which ionize by dissociative electron capture. This was demonstrated by the selective detection of 4,4′-dibromobiphenyl from the components of a polychlorinated biphenyl mixture (Aroclor 1248).     

Ion mobility spectrometry detection for gas chromatography

The hyphenated analytical method in which ion mobility spectrometry (IMS) is coupled to gas chromatography (GC) provides a versatile alternative for the sensitive and selective detection of compounds after chromatographic separation. Providing compound selectivity by measuring unique gas phase mobilities of characteristic analyte ions, the separation and detection process of gas chromatography-ion mobility spectrometry (GC-IMS) can be divided into five individual steps: sample introduction, compound separation, ion generation, ion separation and ion detection. The significant advantage of a GC-IMS detection is that the resulting interface can be tuned to monitor drift times/ion mobilities (as a mass spectrometer (MS) can be tuned to monitor ion masses) of interest, thereby tailoring response characteristics to fit the need of a given separation problem. Because IMS separates ions based on mobilities rather than mass, selective detection among compounds of the same mass but different structures are possible. The most successful application of GC-IMS to date has been in the international space station. With the introduction of two-dimensional gas chromatography (2D-GC), and a second type of mobility detector, namely differential mobility spectrometry (DMS), GC prior to mobility measurements can now produce four-dimensional analytical information. Complex mixtures in difficult matrices can now be analyzed. This review article is intended to provide an overview of the GC-IMS/DMS technique, recent developments, significant applications, and future directions of the technique.     

Analysis of explosives using differential mobility spectrometry

Characterization of ions from eight explosives (2,4,6-trinitrotoluene, pentaerythritol tetranitrate, 2,4,6-trinitrophenol, 2,4-dinitrotoluene, erythritol tetranitrate, hexamethylene triperoxide diamine, 2,4,6-trinitrophenylmethylnitramine and 1,3,5-trinitro-perhydro-1,3,5-triazine) using differential mobility spectrometry (DMS) with ⁶³Ni as an ionization source was performed. Presented results of explosive analysis have been evaluated by use of special software tool which communicates with DMS in real time. This tool was developed for visualization, identification and comparison of measured data. Each explosive provides characteristic signal at a specific compensation voltage under a fixed dispersion field. Peaks in DMS spectra for these ions were confined to a range of compensation voltages between ?1.61 to +1.71 V at RF = 1060 V. We calculated specific alpha coefficients (α₂ and α₄) to obtain a nonlinear function of explosives, based on their DMS spectra. Dependence of mobility for measured explosives ions in electric field at E/N values between 0 to 120 Td were used to inspectional graphical differentiation of explosives.     

Identity confirmation of drugs and explosives in ion mobility spectrometry using a secondary drift gas

This work demonstrated the potential of using a secondary drift gas of differing polarizability from the primary drift gas for confirmation of a positive response for drugs or explosives by ion mobility spectrometry (IMS). The gas phase mobilities of response ions for selected drugs and explosives were measured in four drift gases. The drift gases chosen for this study were air, nitrogen, carbon dioxide and nitrous oxide providing a range of polarizability and molecular weights. Four other drift gases (helium, neon, argon and sulfur hexafluoride) were also investigated but design limitations of the commercial instrument prevented their use for this application. When ion mobility was plotted against drift gas polarizability, the resulting slopes were often unique for individual ions, indicating that selectivity factors between any two analytes varied with the choice of drift gas. In some cases, drugs like THC and heroin, which are unresolved in air or nitrogen, were well resolved in carbon dioxide or nitrous oxide.     

In Situ Explosive Detection Using a Miniature Plasma Ion Source and a Portable Mass Spectrometer

A small low-temperature plasma (LTP) ionization probe was coupled to a portable mass spectrometer for the rapid detection of trace explosives on surfaces. Using only a small diaphragm pump to supply ambient air to the LTP source, 100 ng each of pentaerythritol tetranitrate (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 2,4,6-trinitrophenylmethylnitramine (Tetryl) were detectable on glass in under 1 minute. The main ion signal from these molecules (M) is the [M + NO₃]^? species. While much optimization remains, it is believed that this miniature LTP source will remove the need for external gas cylinders and additional heating for in situ explosives detection using portable mass spectrometers.     

Liquid chromatography/electrospray ionization/ion mobility spectrometry of chlorophenols with full flow from large bore LC columns

Chlorophenols (CPs) as a mixture of fourteen congeners from mono- to pentachlorophenol were determined using liquid chromatography/electrospray ionization/ion mobility spectrometry (LC/ESI/IMS) to describe the response and analytical performance of a mobility spectrometer as a detector for liquid chromatography. The mobility spectrometer was equipped with an interface so that flows from a large bore column could be electrosprayed directly into the drift tube at flow rates up to 500 μL/min without splitting of flow. A linear gradient of the mobile phase from 40% to 90% methanol and 60% to 10% acetic acid (AcOH)–ammonium acetate buffer solution over 40 min with a C18 column provided baseline separations though mobility spectra for CPs were influenced by mobile phase composition. Product ions formed from CPs with ESI included phenoxide anions CPO^?, AcOH·CPO^?, CPOH·CPO^?, and Na⁺·(CPO^?)₂ and were found to be governed by the drift gas temperature. Ions were identified using LC/ESI/mass spectrometry (MS) and supported by results from computational modeling. Quantitative response was affected by congener structure through the acidities of the OH moiety and by the composition of the mobile phase. Limits of detection ranged from 0.135 mg/L for 2,3,5-trichlorophenol and pentachlorophenol to 2.23 mg/L for 2-chlorophenol; corresponding linear ranges were 20 and 70.     

A field test for the detection of peroxide-based explosives

A rapid and simple field test for the detection of triacetone-triperoxide (TATP) and hexamethylenetriperoxidediamine (HMTD), two explosives which find significant illegal use, has been developed. Unknown samples are first treated with a catalase solution to remove hydrogen peroxide traces, in order to provide selectivity towards peroxide-based bleaching agents which are contained in commercial laundry detergents. Subsequently, the peroxide-based explosives are decomposed via UV irradiation, thus yielding hydrogen peroxide, which is determined by the horseradish peroxidase (POD) catalysed formation of the green radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS). The limits of detection for this method are 8 x 10(-6) mol dm(-3) for TATP and 8 x 10(-7) mol dm(-3) for HMTD, respectively. As an option, p-hydroxyphenylacetic acid (pHPAA) may be used as peroxidase substrate, resulting in lower limits of detection (8 x 10(-7) mol dm(-3) for TATP and HMTD). The complete method uses a mobile setup to be applied under field conditions.     

Halogenated compound response in an oxygen doped ion mobility detector for capillary gas chromatography

An ion mobility detector that has been specifically developed for interfacing with capillary gas chromatography is investigated in the negative ion mode. Like the electron capture detector, to which this instrument is closely related, the ion mobility detector shows an enhanced response to low molecular weight halogenated compounds when a small quantity of oxygen is doped into the make-up gas flow. Under O₂ doping conditions, the device can operate in a reactant ion monitoring mode responding universally to compounds capable of capturing thermal electrons and in a tunable selective product ion mode providing increased selectivity over that achieved by the ECD. At an oxygen concentration of 0.5%, minimum detectable amounts as low as 600 femtograms have been realized for carbon tetrachloride. Selectivity of chloro- versus bromo- compounds is demonstrated using a mixture of p-dichlorobenzene and p-dibromobenzene.     

Resistively heated temperature programmable silicon micromachined gas chromatography with differential mobility spectrometry

A microfabricated electromechanical system based on radio frequency modulated ion mobility spectrometry (MEMS-RFIMS), also known as differential ion mobility spectrometry (DMS) has been successfully interfaced to a custom-fabricated resistively heated temperature programmable micromachined gas chromatograph. In contrast to a conventional time-of-flight ion mobility spectrometer, the DMS uses the non-linear mobility dependence in strong radio frequency electric fields for ion filtering. Selective and sensitive detection of targeted analytes of interest can be achieved by using different transport gases, radio frequencies, and associated compensation voltages. In addition, the detection of both positive and negative ions, depending on the ionization mechanism favorable to the analytes involved is achieved. When compared to a stand-alone GC with a non spectrometric detector or a stand-alone DMS, GC-DMS as a hyphenated technique offers two competitive advantages; two orthogonal separating methods in a single analytical system and the resolving power of gas chromatography to minimize charge exchange in the ionization chamber of the detector. In this article, a portable, resistively heated temperature programmable silicon machined gas chromatograph with differential mobility detection is introduced. The performance of the instrument is illustrated with examples of difficult industrial applications.     

Nanoclusters formation in ion mobility spectrometry and change separation selectivity of picoline isomers

Ion mobility spectrometry (IMS) was applied to determine the influence of structural features of nanocluster formation of picoline isomers in ion mobility spectrometry. Since the results of our studies show that different isomers have the same mobilities in pure nitrogen buffer gas and their corresponding peaks are totally overlapped, 2-butanol vapor was introduced into buffer gas by means of an online system from 0 to 300 mL min^?1. We found different structural features of these isomeric compounds which cause distinct differences in ion mobility spectra. These differences result from the formation of different nanocluster product ions (~1 nm³) with different cross section areas formed depending on the occurrence of certain structural features (position of the methyl group on the pyridine ring). The size of cluster product ions formed was determined using cross section area measurements. The effects of temperature in the range from 80 to 200 °C and electric field strength have also been investigated. At 140–160 °C and 636 V cm^?1, optimum peak-to-peak resolution can be obtained.     

Comparative measurements of toxic industrial compounds with a differential mobility spectrometer and a time of flight ion mobility spectrometer

Small concentrations of toxic compounds in atmospheric air have often to be measured selectively by portable equipment. Ion mobility spectrometers are instruments used to monitor explosives, drugs and chemical warfare agents. First responders also need to detect hazardous gases released in accidents while transporting them or in their production in chemical plants. Not all toxic gases can be measured with the time of flight ion mobility spectrometer at concentrations required by safety standards applied in workplace areas. The time of flight ion mobility spectrometer is based on an inlet membrane, an ionization region, a shutter grid and the drift region with a detector in the drift tube. The separation of ions is due to the different mobility of the ions when they are exposed to a weak electric field (E = 200…300 V/cm). High field asymmetric waveform spectrometry or differential mobility spectrometry is a relative new ion mobility spectrometer technology. The separation is due to the different mobilities of the ions in the high (E = 15000...30000 V/cm) and the weak electric fields. About 30 different toxic industrial chemical compounds were analyzed with both systems under comparable conditions. For selected examples the detection limits, the selectivity and the identification capabilities of the two systems for some of the main compounds will be discussed.     

A novel ion detector aiming at the homogeneous of drift gas

In standalone ion mobility spectrometry (IMS) instruments, the effect of drift gas turbulence reduces the sensitivity and resolution of the instrument. A traditional ion detector constructed with a Faraday plate and used to detect ions in an IMS is positioned at the end of the drift region. Drift gas flowing through this detector may introduce turbulence near the detector, possibly affecting the sensitivity and resolution of the device. To address this problem, a novel Faraday detector with a double layer structure was constructed. A number of dense and staggered holes were created on each layer of the detector. This design enabled the drift gas to pass through the holes of the detector, and the staggered nature of holes in the detector ensured that the ions could be detected. Theoretical simulations were conducted using the finite element method to obtain velocity distributions for both a standard Faraday detector and the modified Faraday detector. The results indicated that the novel ion detector created a homogenous gas under at high inlet flow rate while turbulence was still evident for the traditional Faraday detector. When the inlet flow rate was 1000 mL/min, the range of the unstable region of the drift gas in the axis of the drift tube with the novel ion detector was reduced by 97% relative to that for the traditional detector. The data suggests that due to such gains, sensitivity and resolution may be improved for standalone IMS instruments.     

Paper spray ionization with ion mobility spectrometry at ambient pressure

A paper spray ion source was combined with a drift tube operating at ambient pressure for mobility measurements of ions derived from pharmaceutical solutions. Paper spray ionization with solvent alone resulted in a mixture of ions convolved to a single peak with a reduced mobility of 2.19 cm²/Vs in the mobility spectrum. These were mass-identified principally as m/z 157, (MeOH)₂(HCOOH)₂H⁺ and m/z 129, (MeOH)₄(H₂O)H⁺ while pharmaceuticals with nitrogen bases formed MH⁺ product ions. The duration of response was governed by the volume of liquid added to the paper source and was limited by evaporation of solvent in gas at 58 °C venting the drift tube. Quantitative variation was attributed in part to morphologic changes in the tip of the paper spray source. This was associated with mass flow in the electrical discharge and not due alone to cycles of wetting and drying of the paper. Mobility spectra of chlorpromazine in urine, exhibited a single product ion peak and linear response was 30 to 500 ng with an estimated limit of detection of 1.5 ng. Ion flux could be prolonged by continuous addition of liquid and findings portend a combination of paper spray ionization IMS with paper chromatography.     

Peak capacity in differential mobility spectrometry: effects of transport gas and gas modifiers

Differential mobility spectrometry (DMS) can be used as a pre-filter to improve selectivity prior to mass spectral analysis, because it provides an additional mobility based separation to mass analysis. Ions within a differential mobility spectrometer are separated based upon differences in mobility behavior, which are manifested by applying a strong high frequency asymmetric RF waveform. Currently it is well documented that DMS separation power (peak capacity), can be substantially augmented by adding chemical modifiers to the transport gas. This process is generally referred to as the dynamic cluster/decluster model, and it occurs due to gas phase processes when analyte ions are clustered with modifier molecules in the lower field portion of the RF pulses and declustered during the higher field portion of the waveform. Previous publications have demonstrated that the planar electrode geometry is key to realizing improved performance of DMS sensors with high concentrations of chemical modifiers. The clustering modifier is provided with sufficient concentration to reach conditions where separation peak capacity can be substantially augmented (typically around 1.5?%). The present paper expands on these previous findings by mapping out the behavior of structurally similar compounds, including structural isomers, with a series of different transport gas modifiers, including isopropanol, methanol, acetonitrile, acetone, and ethylacetate. The results highlight the importance of analyte/modifier interactions, demonstrating the variability that can be achieved when different modifiers are used.     

Fourier transform ion mobility spectrometry of barbiturates after capillary gas chromatography

This paper demonstrates a novel operating mode of an ion mobility detector (IMD) for obtaining both qualitative and quantitative data after capillary gas chromatographic separation of 5,5′-disubstituted barbiturates. Using a recently developed time dispersive Fourier transform method for ion mobility spectrometry, complete ion mobility spectra could be obtained for each component in the chromatogram. This type of spectra can be used for providing qualitative information on unknown compounds or for selecting the proper detector conditions needed when operating in the continuous mobility monitoring mode. In this study each of the five barbiturates investigated produced a Fourier transformed ion mobility spectrum containing one major product ion. When drift times corresponding to those of the product ions measured in the FT mode were monitored continuously, selective chromatographic detection of the barbiturates was achieved. In one case even isomers could be differentiated based on mobility characteristics.     

Gas chromatography with state-of-the-art micromachined differential mobility detection: operation and industrial applications

Ion mobility spectrometry (IMS) has potential analytical applications in very diverse fields such as chemical, petrochemical, environmental, and, more recently, in drug, chemical warfare agent, and explosives detection. Commercially available IMS instruments are based on time-of-flight (TOF) mass spectrometry. IMS is inherently suitable for field operation as it uses relatively simple microfluidic devices and operates at atmospheric pressure. It is portable, highly sensitive with tunable selectivity, yet can be produced at relatively low cost. Key limitations of this analytical detection technique are low duty cycle, ion cluster formation, short linear dynamic range, and restriction to only positive or negative ion collection in a single analysis. Microelectromechanical system, radio frequency modulated IMS (MEMS RF-IMS), also known as differential mobility spectrometry, has recently been developed and commercialized. The technology is based on IMS, and MEMS RF-IMS offers substantially better performance. In this study, the strengths and limitations of the recently introduced differential mobility detector when used with gas chromatography in trace analyses are discussed and illustrated with applications of industrial significance.     

A critical review of ion mobility spectrometry for the detection of explosives and explosive related compounds

Ion mobility spectrometry has become the most successful and widely used technology for the detection of trace levels of nitro-organic explosives on handbags and carry on-luggage in airports throughout the US. The low detection limits are provided by the efficient ionization process, namely, atmospheric pressure chemical ionization (APCI) reactions in negative polarity. An additional level of confidence in a measurement is imparted by characterization of ions for mobilities in weak electric fields of a drift tube at ambient pressure. Findings from over 30 years of investigations into IMS response to these explosives have been collected and assessed to allow a comprehensive view of the APCI reactions characteristic of nitro-organic explosives. Also, the drift tube conditions needed to obtain particular mobility spectra have been summarized. During the past decade, improvements have occurred in IMS on the understanding of reagent gas chemistries, the influence of temperature on ion stability, and sampling methods. In addition, commercial instruments have been refined to provide fast and reliable measurements for on-site detection of explosives. The gas phase ion chemistry of most explosives is mediated by the fragile CONO(2) bonds or the acidity of protons. Thus, M(-) or M.Cl(-) species are found with only a few explosives and loss of NO(2), NO(3) and proton abstraction reactions are common and complicating pathways. However, once ions are formed, they appear to have stabilities on time scales equal to or longer than ion drift times from 5-20 ms. As such, peak shapes in IMS are suitable for high selectivity and sensitivity.     

Investigation of neuroleptics and other aromatic compounds by laser-based ion mobility mass spectrometry

Laser-based ion mobility (IM) spectrometry was used for the detection of neuroleptics and PAH. A gas chromatograph was connected to the IM spectrometer in order to investigate compounds with low vapour pressure. The substances were ionized by resonant two-photon ionization at the wavelengths λ?=?213 and 266 nm and pulse energies between 50 and 300 μJ. Ion mobilities, linear ranges, limits of detection and response factors are reported. Limits of detection for the substances are in the range of 1–50 fmol. Additionally, the mechanism of laser ionization at atmospheric pressure was investigated. First, the primary product ions were determined by a laser-based time-of-flight mass spectrometer with effusive sample introduction. Then, a combination of a laser-based IM spectrometer and an ion trap mass spectrometer was developed and characterized to elucidate secondary ion–molecule reactions that can occur at atmospheric pressure. Some substances, namely naphthalene, anthracene, promazine and thioridazine, could be detected as primary ions (radical cations), while other substances, in particular acridine, phenothiazine and chlorprothixene, are detected as secondary ions (protonated molecules). The results are interpreted on the basis of quantum chemical calculations, and an ionization mechanism is proposed.