Ion Mobility Spectrometry Spectra Research Articles

Rapid analysis of tile industry gaseous emissions by ion mobility spectrometry and comparison with solid phase micro-extraction/gas chromatography/mass spectrometry

The present paper reports on a rapid method for the analysis of gaseous emissions from ceramic industry, based on ion mobility spectrometry (IMS) as a means for on-site monitoring of volatile organic compounds (VOCs) produced during tile baking. IMS was calibrated with a set of reference compounds (i.e. ethyl acetate, ethanol, ethylene glycol, diethylene glycol, acetaldehyde, formaldehyde, 2-methyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 1,3-dioxolane, 1,4-dioxane, benzene, toluene, cyclohexane, acetone, acetic acid) via air-flow permeation. The technique was tested on a laboratory-scale kiln and tiles prepared with selected glycol- and resin-based additives. Finally, the analytical method was applied to emissions from two industries in the Modena (Italy) ceramic area. The results of all experimental phases were compared to those obtained by solid phase micro-extraction/gas chromatography/mass spectrometry (SPME/GC/MS). IMS showed potential as a real-time monitoring device for quality assessment in ceramic industry emissions. IMS spectra, SPME/GC/MS data, relationship between additives/baking conditions and produced VOCs and advantages and limitations of both techniques will be discussed.

Comparing the effect of pressure and temperature on ion mobilities

The effect of pressure on ion mobilities has been investigated and compared with that of temperature. In this connection, an ion mobility spectrometry (IMS) cell, which employs a corona discharge as the ionization source, has been designed and constructed to allow varying pressure inside the drift region. IMS spectra were recorded at various pressures ranging from 15 Torr up to atmospheric pressure. The results show that IMS peaks shift perfectly linear with pressure which is in excellent agreement with the ion mobility theory. However, experimental ion mobilities versus temperature show deviation from the theoretical trend. The deviation is attributed to formation of clusters. The different behaviour of pressure and temperature was explained on the basis of the different impact of pressure and temperature on hydration and clustering of ions. Pressure affects the clustering reactions linearly but temperature affects it exponentially.

A novel electron source for negative ion mobility spectrometry

The possibility of using negative corona discharge in pure nitrogen as the ionization source for negative ion mobility spectrometry (IMS) has been investigated. The discharge in pure nitrogen produces a huge number of electrons, almost 10 6 times as much as that produced by the conventional 63 Ni ionization source. However, this high intensity electron source cannot be simply used in IMS since introducing any electronegative substance in the corona region immediately results in quenching of the discharge. In this connection, a special IMS cell has been designed and optimized to employ this intense electron source without being disturbed by sample. With this design, the electron current received at the detector plate could be as high as 200 nA. The ionization efficiency and the collection efficiency of the electrons and negative ions, as a function of electric field at different regions, have been evaluated. As practical examples, the IMS spectra of CHCl 3, CHBr 3, CH 3I and nitrobenzene, as well as the explosive materials pentaerythritol tetranitrate (PETN) and trinitrotoluene (TNT) at elevated temperatures have been obtained. Finally, the capability of the method in quantitative analysis of CHCl 3 has been evaluated and a detection limit of 10 ng/m 3 and a linear range of five orders of magnitude were obtained.

Two-dimensional separations with electrospray ionization ambient pressure high-resolution ion mobility spectrometry/quadrupole mass spectrometry.

The coupling of ion mobility spectrometry (IMS) instruments with mass spectrometers has been described since early in IMS development, most commonly with quadrupole mass analyzers. The recent development of IMS with time-of-flight (TOF) instruments has demonstrated that the time compatibility (IMS milliseconds and TOFMS microseconds) of the two techniques enables rapid two-dimensional separations to be performed, theoretically in the order of seconds for a complete analysis. This study presents a unique way to operate a traditional IMS/QMS system to attain separations similar to those achieved with IMS/TOF. For this new approach, the quadrupole was slowly scanned in the single-ion monitoring mode while IMS spectra were continually embedded in each m/z step. In this way, two-dimensional separations (IMS drift times and m/z) were obtained using the traditional IMS/QMS arrangement. An example of a five amino acid separation (quadrupole scan of 40 m/z values at a rate of approximately 7 steps/min) led to a complete two-dimensional analysis within 6 min, comparable to rapid chromatographic separations with mass spectrometry. Proposed approaches to reduce the analysis time are discussed and a reduction in the analysis time to less than 1 min is feasible when the IMS/QMS separation conditions are optimized.

Evaluation of micro-electrospray ionization with ion mobility spectrometry/mass spectrometry

In recent years, the resolving power of ion mobility instruments has been increased significantly, enabling ion mobility spectrometry (IMS) to be utilized as an analytical separation technique for complex mixtures. In theory, decreasing the drift tube temperature results in increased resolution due to decreased ion diffusion. However, the heat requirements for complete ion desolvation with electrospray ionization (ESI) have limited the reduction of temperatures in atmospheric pressure ion mobility instruments. Micro-electrospray conditions were investigated in this study to enable more efficient droplet formation and ionization with the objective of reducing drift tube temperatures and increasing IMS resolution. For small molecules (peptides), the drift tube temperature was reduced to ambient temperature with good resolution by employing reduced capillary diameters and flow rates. By employing micro-spray conditions, experimental resolution values approaching theoretically predicted resolution were achieved over a wide temperature range (30 to 250 °C). The historical heat requirements of atmospheric pressure IMS due to ESI desolvation were eliminated due to the use of micro-spray conditions and the high-resolution IMS spectra of GLY-HIS-LYS was obtained at ambient temperature. The desolvation of proteins (cytochrome c) was found to achieve optimal resolution at temperatures greater than 125 °C. This is significantly improved from earlier IMS studies that required drift tube temperatures of 250°C for protein desolvation.

Evaluation of capillary liquid chromatography–electrospray ionization ion mobility spectrometry with mass spectrometry detection

Due to the proteomics revolution, multi-dimensional separation and detection instruments are required to evaluate many peptides and proteins in single samples. In this study, electrospray ionization (ESI) ion mobility spectrometry (IMS) was evaluated as an additional separation after HPLC separations. Common HPLC mobile phase compositions (solvents, acid modifiers, and buffers) were assessed for the effect on ESI-IMS response. Up to 5 m M sodium phosphate, a non-volatile buffer, was able to be electrosprayed into the IMS without degradation of the instrumental performance. Due to the rapid separation times of IMS, multiple IMS spectra were obtained within a single HPLC peak. A five-peptide mixture was separated in a capillary HPLC column under isocratic conditions within 3 min. Coelution of two peaks due to non-optimal HPLC conditions occurred and these two peaks could not be distinguished by HPLC with UV detection. In contrast, the single ion mobility chromatograms provided separation of each peptide as well as providing a second degree of analyte identification (HPLC retention time and IMS mobility). Furthermore, IMS–MS analysis of the five peptides and comparison with HPLC retention times showed that each peptide had a unique retention time–ion mobility–mass to charge value. This work showed that IMS could be employed for direct separation and detection of HPLC eluents and also could be combined with HPLC–MS for three unique dimensions of separation.

Monitoring Odorous Sulfur Emissions Using Self-Organizing Maps for Handling Ion Mobility Spectrometry Data

ABSTRACT Possibilities for monitoring emissions of reduced sulfur compounds in pulp and paper mills were investigated using ion mobility spectrometry (IMS) and a self-organizing map (SOM) algorithm. The reduced sulfur compounds measured were hydrogen sulfide (H2S), dimethyl sulfide (DMS), and methyl mercaptan (MM). Attention was paid to momentary concentrations because there is no monitoring device able to measure peak concentrations of reduced sulfur compounds under field conditions. These methods were evaluated by measuring the reduced sulfur compounds first in the laboratory and then at a process monitoring site at a pulp factory. The aim was to find out whether it would be possible to use the laboratory measurements to recognize the same reduced sulfur compounds at the monitoring site. Data collection was followed by analysis using the SOM algorithm and Sammon's mapping. The results showed that the IMS spectra of reduced sulfur compounds and their mixtures can be distinguished from each other by computationally intelligent methods and that the spectra from the process monitoring site corresponded with the laboratory measurements to a certain extent.

Selective Determination of Dimethoate Using Ion Mobility Spectrometry with Single and Mixed Alternate Reagent Ions

Dimethoate, one of the organophosphorus pesticides, was selectively determined by ion mobility spectrometry (IMS) along with the single and mixed alternate reagent ions. By doping ammonium, acetone, ethanol, ether, and methanol into the carrier gas, the best selective detection was obtained by the addition of ammonium having the highest proton affinity among these single alternate reagent ions. Three mixed alternate reagents including ammonium−acetone, ammonium−ether, and acetone−ether, which were also used to improve the selectivity, showed better results than that single-solvent dopants gained. The best resolution and the highest abundance of the dimethoate peak were observed in its IMS spectrum after the addition of the mixed ammonium−acetone among all the above-mentioned dopants. The relationship curves for the concentration of ammonium and mixed ammonium−acetone to the response of dimethoate were studied. Ammonium at ∼1.0 μg/L levels or 1.0 μg/L ammonium at plus acetone at ∼1.0 μg/L levels exhibited the strongest response of dimethoate. In addition, the direct determination of dimethoate residues was compared to its selective detection with mixed ammonium−acetone as the alternate reagent ions in a field test. A model for the selective analysis of an analyte having middle proton affinity in mixed compounds is proposed.

Reaction of Chloride Ion with Isopropyl Bromide at Atmospheric Pressure by Ion Mobility Spectrometry

The SN2 nucleophilic displacement reaction of chloride ion with isopropyl bromide (i-PrBr) has been studied in nitrogen buffer gas at a pressure of 640 Torr over the temperature range 20−175 °C by ion mobility spectrometry (IMS). It is concluded that, under these conditions of relatively high buffer gas pressure, this nucleophilic displacement reaction occurs primarily by the distinctly two-step mechanism Cl- + i-PrBr ⇌ Cl-(i-PrBr) → Br- + i-PrCl in which a thermal energy ion complex, Cl-(i-PrBr), is maintained in a state of chemical equilibrium with the reactants. An SN2 displacement reaction then occurs within the thermal energy cluster ion by its unimolecular conversion to products. Equilibrium constants, K1, and rate constants, k1, for Cl- + i-PrBr ⇌ Cl-(i-PrBr) and Cl-(i-PrBr) → Br- + i-PrCl, respectively, are determined from the IMS spectra as a function of temperature. In addition, second-order clustering to form the ion complex Cl-(i-PrBr)2 is also observed, and equilibrium constants, K2, for this...

Application of neural networks for interpretation of ion mobility and x-ray fluorescence spectra

Neural networks (NN) have been successfully used to interpret spectral data, and to derive qualitative and quantitative information from ion mobility spectrometry (IMS) and x-ray fluorescence (XRF). It is shown that components of complex mixtures of up to six aliphatic amines may be automatically identified by NN methods from their ion mobility spectra with reasonable accuracy. The ability of NN to identify compounds even under low signal-to-noise conditions of IMS spectra is demonstrated. The use of XRF technique for quantitative determination of parts per million (ppm) amounts of mixtures of Re, Os, Ir and Pt in a polyethylene matrix, which could not be done successfully by conventional methods, was made possible by application of NN, with a root mean square error of a few ppm. The networks could be trained on a personal computer, in less than 10 min, from a surprisingly small data set of training samples to perform these tasks.