Characterization of a miniature, ultra-high-field, ion mobility spectrometer

By combining a multiple micron-gap ion separator with a novel high-frequency separation waveform drive topology, it has been possible to considerably extend the separation field limits employed in Field Asymmetric Ion Mobility Spectrometry (FAIMS)/Differential Mobility Spectrometry (DMS); giving rise to an Ultra-High-Field operational domain. A miniature spectrometer, based around the multi-micron-gap ion separator and ultra-high-field drivers, has been developed to meet the continuing industrial need for sensitive (sub-ppm), broadband and fast (second timescale) response volatile chemical detection. The packaged miniature spectrometer measures 12?×?12?×?15?cm, weighs 1.2?kg and is fully standalone; consisting of the core multi-micron gap ion separator assembly and RF/DC electronic drivers integrated with pneumatic handling/sample conditioning elements, together with ancillary temperature, flow and humidity sensing for stable closed loop operation (under local microprocessor control). The combination of multiple micron-gap ion separators with the novel high-frequency separation waveform drive topology enables ion separations to be performed over scanning electric field ranges of 0 to >75?kV·cm^?1 (0 to >??320 Td at 101?kPa), offering a potential solution to trace and ultra-trace chemical detection/monitoring problems, that conventional IMS and DMS/FAIMS may otherwise find challenging. In this ultra-high field operational regime effective ion temperatures may be ??swept?? from ambient to >1000 K because critically, the effective ion temperature scales to at least the square of the applied field. With this field induced ion heating a controlled manipulation (or switching) of the ion chemistry within the separation channel (the ion drift region) may be invoked. For example, ion fragmentation via thermal dissociation can be induced. Chemical separation and identification is thus derived from the unique kinetic and thermodynamic behavior of ions assessed over a very broad effective temperature range. In addition to describing the novel miniature spectrometer, this paper addresses key aspects of ultra-high-field operation, which render it distinct from traditional ion mobility technologies and principles. In particular, this paper essays a model of ultra-high-field operation and highlights model deviations, whilst providing clear theoretical explanation backed up with experimental evidence.     

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.     

离子迁移谱法检测圣女果中的敌敌畏和马拉硫磷

建立了采用便携式离子迁移谱仪(IMS)对敌敌畏和马拉硫磷进行快速检测的分析方法.在大气压条件下,以63Ni作为电离源,干燥洁净的空气作为载气和迁移气,采用负离子模式进行操作,气路采用闭路循环模式.在优化条件下(进样口温度为180 ℃,迁移管温度为150 ℃,载气流量和迁移气流量均为0.6L/min)进行检测,敌敌畏和马...     

Comprehensive software suite for the operation, maintenance, and evaluation of an ion mobility spectrometer

Scientific applications of Ion Mobility Spectrometry require the ability to easily compare data between different laboratories. Reduced mobility values attempt to provide this functionality, but no standard exists for the collection and manipulation of the raw data obtained during an IMS experiment. We have created a comprehensive software suite based on the LabVIEW programming language that can be used to collect and interpret IMS data. The software may be used to collect data from a stand-alone IMS cell, a voltage sweep IMS cell, or a coupled chromatography-IMS system, and this framework may be adapted to incorporate mass spectral data analysis as well. This software is provided under an open source license for the benefit of the IMS community.     

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.     

Ion trapping at atmospheric pressure (760 Torr) and room temperature with a high-field asymmetric waveform ion mobility spectrometer

A method for the confinement of ions at 760 Torr and room temperature is described. We have recently shown that a cylindrical-geometry high-field asymmetric waveform ion mobility spectrometer (FAIMS), which utilizes an ion separation technique based on the change in ion mobility at high electric fields, focuses ions in two dimensions. This article describes a FAIMS device in which the focusing is extended to three dimensions (i.e. ion trap). Characterization of the ion trap was carried out using a laboratory-constructed time-of-flight mass spectrometer. The half-life of a m/z 380 ion in the trap was determined to be 5 ms.     

Construction and characterization of a high-flow, high-resolution ion mobility spectrometer for detection of explosives after personnel portal sampling

A novel analysis of explosives via the coupling of an airline passenger personnel portal with a high-flow (HF), high-resolution (HR) ion mobility spectrometry (IMS) was shown for the first time. The HF-HR-IMS utilized a novel ion aperture grid design with a (63)Ni ionization source while operating at ambient pressure in the positive ion mode at 200 degrees C. The HF-HR-IMS response characteristics of 2,4,6-trinitrotoluene (TNT), 4,6-dinitro-o-cresol (4,6DNOC), and cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) were investigated. Modifications made to the HF-HR-IMS exhaust and ionization source created an 800% increase in the total ion current (TIC), from 0.85 to 6.8 nA. This translated into a 65% ion response increase for TNT when compared with a traditional IMS. A mixture of TNT and (4,6DNOC) was used to successfully demonstrate the resolving power of the species with similar reduced mobility constants (K(o)), 1.54 and 1.59, respectively. The reactant ion (H(2)O)(n)H(+), peak was also used to measure the resolving power of the spectrometer while varying the internal diameter of three different aperture openings from 1.00 to 3.54cm. This provided a resolving power range of 50-60, double that typically achievable by commercial IMS instruments. Most important, these changes made in this new instrumental design can be implemented to all existing and future IMS's to greatly enhance the achievable IMS resolving power.     

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the eff ects of polarizable drift gases and ionic charge distribution

We have studied the behavior of isomers and analogues by traveling wave ion mobility mass spectrometry (TWIM‐MS) using drift‐gases with varying masses and polarizabilities. Despite the reduced length of the cell (18 cm), a pair of constitutional isomers, N‐butylaniline and para‐butylaniline, with theoretical collision cross‐section values in helium (Ω_He) differing by as little as 1.2 Ų (1.5%) but possessing contrasting charge distribution, showed baseline peak‐to‐peak resolution (R_p‐p) for their protonated molecules, using carbon dioxide (CO₂), nitrous oxide (N₂O) and ethene (C₂H₄) as the TWIM drift‐gas. Near baseline R_p‐p was also obtained in CO₂ for a group of protonated haloanilines (para‐chloroaniline, para‐bromoaniline and para‐iodoaniline) which display contrasting masses and theoretical Ω_He, which differ by as much as 15.7 Ų (19.5%) but similar charge distributions. The deprotonated isomeric pair of trans‐oleic acid and cis‐oleic acid possessing nearly identical theoretical Ω_He and Ω_N2 as well as similar charge distributions, remained unresolved. Interestingly, an inversion of drift‐times were observed for the 1,3‐dialkylimidazolium ions when comparing He, N₂ and N₂O. Using density functional theory as a means of examining the ions electronic structure, and He and N₂‐based trajectory method algorithm, we discuss the effect of the long‐range charge induced dipole attractive and short‐range Van der Waals forces involved in the TWIM separation in drift‐gases of differing polarizabilities. We therefore propose that examining the electronic structure of the ions under investigation may potentially indicate whether the use of more polarizable drift‐gases could improve separation and the overall success of TWIM‐MS analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of a new miniaturized ion mobility spectrometer and its coupling to fast gas chromatography multicapillary columns

A new miniaturized ion mobility spectrometer (microIMS) has been constructed and evaluated. The results obtained for a selected group of volatile organic compounds have been compared with those provided by an IMS of bigger dimensions with satisfactory conclusions. Moreover, its performance in terms of analytes resolution is better than those values given for other miniaturized instruments described in the literature. The possibility of an adjustable shutter opening time and the low intensity of the radiation source are also remarkable characteristics of the miniaturized detector. The small size of the microIMS enables its portability and its wide-range of applications as a sensor device. Six different substances supposed as respiratory markers of different diseases have been selected to prove the feasibility of the spectrometer constructed.     

Atmospheric-pressure ionization studies and field dependence of ion mobilities of isomeric hydrocarbons using a miniature differential mobility spectrometer

The ionization pathways and ion mobility were determined for sets of structural isomeric and stereoisomeric non-polar hydrocarbons (saturated and unsaturated cyclic hydrocarbons and aromatic hydrocarbons) using a novel miniature differential mobility spectrometer with atmospheric-pressure photoionization (APPI) to assess how structural and stereochemical differences influence ion formation and ion mobility. The analytical results obtained using the differential mobility spectrometry (DMS) were compared with the reduced mobility values measured using conventional time-of-flight ion mobility spectrometry (IMS) with the same ionization technique.The majority of differences in DMS ion mobility spectra observed among isomeric cyclic hydrocarbons can be explained by the formation of different product ions. Comparable differences in ion formation were also observed using conventional IMS and by investigations using the coupling of ion mobility spectrometry with mass spectrometry (APPI-IMS-MS) and APPI-MS. Using DMS, isomeric aromatic hydrocarbons can in the majority of cases be distinguished by the different behavior of product ions in the strong asymmetric radio frequency (rf) electric field of the drift channel. The different peak position of product ions depending on the electric field amplitude permits the differentiation between most of the investigated isomeric aromatics with a different constitution; this stands in contrast to conventional IMS in which comparable reduced mobility values were detected for the isomeric aromatic compounds.     

The role of external electric fields in enhancing ion mobility, drift velocity, and drift-diffusion rates in aqueous electrolyte solutions

Molecular simulations have been carried out using the method of molecular dynamics to investigate the role of external electric fields on the ion mobility, drift velocity, and drift-diffusion rate of ions in aqueous electrolyte solutions. These properties are critical for a range of processes including electrodialysis, electro-deionization, electrophoresis, and electroosmosis. Our results show that external electric fields relax the hydrated ion structure at significantly larger time scales (between 300 and 800 ps), than most other relaxation processes in solutions (generally of the order of 1 ps). Previous studies that did not account for the much longer relaxation times did not observe this behavior for ions even with very high electric fields. External electric fields must also overcome several (at least two or more) activation energy barriers to significantly change the structure of hydrated ions. As a result, the dynamic behavior changes almost in bands as a function of electric field strengths, rather than linearly. Finally, the effect of the field is much less dramatic on water than the ions. Thus electric fields will be of more significance in processes that involve the transport of ions (such as electro-deionization) than the transport of water (electroosmosis).     

High‐resolution extracted ion chromatography,a new tool for metabolomics and lipidomics using a second‐generation orbitrap mass spectrometer

Most analytical methods in metabolomics are based on one of two strategies. The first strategy is aimed at specifically analysing a limited number of known metabolites or compound classes. Alternatively, an unbiased approach can be used for profiling as many features as possible in a given metabolome without prior knowledge of the identity of these features. Using high‐resolution mass spectrometry with instruments capable of measuring m/z ratios with sufficiently low mass measurement uncertainties and simultaneous high scan speeds, it is possible to combine these two strategies, allowing unbiased profiling of biological samples and targeted analysis of specific compounds at the same time without compromises. Such high mass accuracy and mass resolving power reduces the number of candidate metabolites occupying the same retention time and m/z ratio space to a minimum. In this study, we demonstrate how targeted analysis of phospholipids as well as unbiased profiling is achievable using a benchtop orbitrap instrument after high‐speed reversed‐phase chromatography. The ability to apply both strategies in one experiment is an important step forward in comprehensive analysis of the metabolome. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of thiram residues in canola seeds,water and soil samples using solid-phase microextraction with polypyrrole film followed by ion mobility spectrometer

Thiram fungicide contamination in canola seeds, water and soil samples was monitored using headspace solid-phase microextraction (HS-SPME) combined with ion mobility spectrometer (IMS) to assess its environmental relevance. The influence of the various analytical parameters on microextraction procedure including pH, ionic strength, equilibrium time and temperature has been evaluated and optimised. HS-SPME-IMS allowed the determination of thiram in the concentration range of 10–300 ng mL^?1 (R² > 0.99). The detection limit and relative standard deviation were 6 ng mL^?1 and 8% for five replicate analyses, respectively. The HS-SPME-IMS method with polypyrrole film doped with dodecylsulfate (PPy-DS) as solid phase provided an effective sample clean-up for the monitoring of thiram in canola and soil samples. The main advantages of this method are sensitive, good repeatability, organic solvent-free, less time-consuming and relatively inexpensive.     

Coupling desorption electrospray ionisation and neutral desorption/extractive electrospray ionisation with a travelling-wave based ion mobility mass spectrometer for the analysis of drugs

Desorption electrospray ionisation (DESI) and neutral desorption/extractive electrospray ionisation (EESI) have been coupled to a hybrid quadrupole travelling-wave (T-Wave)-based ion mobility time-of-flight mass spectrometer for the direct accurate mass analysis of active ingredients formulated into pharmaceutical samples. The collision cross-section measurements of polyethylene glycol (PEG) excipients detected in one formulation were estimated and compared with published data. These estimated collision cross-sections of the PEG species showed good agreement with published data.