Positive Ion Mobility Spectra Research Articles

Feasibility of corona discharge ion mobility spectrometry for direct analysis of samples extracted by dispersive liquid–liquid microextraction

The capability of corona discharge ionization ion mobility spectrometry (CD-IMS) for direct analysis of the samples extracted by dispersive liquid–liquid microextraction (DLLME) was investigated and evaluated, for the first time. To that end, an appropriate new injection port was designed and constructed, resulting in possibility of direct injection of the known sample volume, without tedious sample preparation steps (e.g. derivatization, solvent evaporation, and re-solving in another solvent…). Malathion as a test compound was extracted from different matrices by a rapid and convenient DLLME method. The positive ion mobility spectra of the extracted malathion were obtained after direct injection of carbon tetrachloride or methanol solutions. The analyte responses were compared and the statistical results revealed the feasibility of direct analysis of the extracted samples in carbon tetrachloride, resulting in a convenient methodology. The coupled method of DLLME-CD-IMS was exhaustively validated in terms of sensitivity, dynamic range, recovery, and enrichment factor. Finally, various real samples of apple, river and underground water were analyzed, all verifying the feasibility and success of the proposed method for the easy extraction of the analyte using DLLME separation before the direct analysis by CD-IMS.

Rapid analysis of captopril in human plasma and pharmaceutical preparations by headspace solid phase microextraction based on polypyrrole film coupled to ion mobility spectrometry

A rapid, simple, and sensitive headspace solid phase microextraction coupled to ion mobility spectrometry (HS-SPME-IMS) method is presented for analysis of the highly specific angiotensin-converting enzyme (ACE) inhibitor, captopril (CAP). Positive ion mobility spectra of CAP were acquired with an ion mobility spectrometer equipped with a corona discharge ionization source. Mass-to-mobility correlation equation was used to identify product ions. A dodecylsulfate-doped polypyrrole (PPy-DS) coating was used as a fiber for SPME. The results showed that PPy-DS based SPME fiber was suitable for successfully extracting CAP from human blood plasma and pharmaceutical samples. The HS-SPME-IMS method provided good repeatability (R.S.D.s < 4%) for aqueous and spiked plasma samples. The calibration graphs were linear in the range of 10–300 ng mL −1 ( R 2 > 0.99) and detection limits were 7.5 ng mL −1 for aqueous and 6.3 ng mL −1 for plasma blank samples. Finally, a standard addition calibration method was applied to HS-SPME-IMS technique for the analysis of blood plasma samples and tablets. Purpose method seemed to be suitable for the analysis of CAP in plasma samples as it is not time consuming (state total time from sample preparation to analysis), it required only small quantities of the sample, and no derivatization was required.

Discriminant Analysis of Fused Positive and Negative Ion Mobility Spectra Using Multivariate Self-Modeling Mixture Analysis and Neural Networks

A new method coupling multivariate self-modeling mixture analysis and pattern recognition has been developed to identify toxic industrial chemicals using fused positive and negative ion mobility spectra (dual scan spectra). A Smiths lightweight chemical detector (LCD), which can measure positive and negative ion mobility spectra simultaneously, was used to acquire the data. Simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) was used to separate the analytical peaks in the ion mobility spectra from the background reactant ion peaks (RIP). The SIMPLSIMA analytical components of the positive and negative ion peaks were combined together in a butterfly representation (i.e., negative spectra are reported with negative drift times and reflected with respect to the ordinate and juxtaposed with the positive ion mobility spectra). Temperature constrained cascade-correlation neural network (TCCCN) models were built to classify the toxic industrial chemicals. Seven common toxic industrial chemicals were used in this project to evaluate the performance of the algorithm. Ten bootstrapped Latin partitions demonstrated that the classification of neural networks using the SIMPLISMA components was statistically better than neural network models trained with fused ion mobility spectra (IMS).

Determination of alcohol compounds using corona discharge ion mobility spectrometry

Ion mobility spectrometry (IMS) is a very fast, highly sensitive, and inexpensive technique, it permits efficient monitoring of volatile organic compounds like alcohols. In this article, positive ion mobility spectra for six alcohol organic compounds have been systematically studied for the first time using a high-resolution IMS apparatus equipped with a discharge ionization source. Utilizing protonated water cluster ions (H 2O) n H + as the reactant ions and clean air as the drift gas, alcohol organic compounds, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-pentanol and 2-octanol, all exhibit product ion characteristic peaks in their respective ion mobility spectrometry, that is a result of proton transfer reactions between the alcohols and reaction ions (H 2O) n H +. The mixture of these alcohols, including two isomers, has been detected, and the results showed that they could be distinguished effectively in the ion mobility spectrum. The reduced mobility values have been determined, which are in very well agreement with the traditional 63Ni-IMS experimental values. The exponential dilution method was used to calibrate the alcohol concentrations, and a detection limit available for the alcohols is in order of magnitude of a few ng/L.

Analysis of Sevin, Amitraz, and Metalaxyl Pesticides Using Ion Mobility Spectrometry

Positive ion mobility spectra of different pesticides, such as sevin or carbaryl (1‐napthyl methylcarbamate), amitraz (N,N′‐[(methylimino) dimethylidyne]di‐2,4‐xylidine), and metalaxyl (methyl‐N‐(2,6‐dimethylphenyl)‐N‐(2‐xylyl)‐DL‐alaninate) as carbamate, amidine, and alkaline groups, respectively, have been studied in air at ambient pressure using ion mobility spectrometry method with 63Ni ionization source. The limits of detection (LODs) were 5.3×10−10, 5.8×10−10, and 4.5×10−10 g for sevin, amitraz, and metalaxyl, respectively. The working range of these compounds was about three orders of magnitude and the relative standard deviation (RSD) of repeatability at the 5 µg mL−1 level were all below 14%. Furthermore, in this study, the influences of IMS cell temperature on the ion mobility spectra of these compounds were investigated.

Determination and identification of malathion, ethion and dichlorovos using ion mobility spectrometry

Positive ion mobility spectra of different organophosphorus pesticides such as malathion ( s-(1,2-dicarb-ethoxyethyl) o, o-dimethyl dithiophosphate), ethion ( o, o, o′, o′-tetraethyl s, s′-methylene bis(phosphorodithioate)) and dichlorovos (2,2-dichlorovinyl dimethyl phosphate) have been studied in air at ambient pressure using ion mobility spectrometry method with 63Ni ionization source. The limits of quantification (LOQs) were 1.0 × 10 −9, 1.0 × 10 −9 and 5.0 × 10 −9 g for malathion, ethion and dichlorovos, respectively. The working range of these compounds was about three orders of magnitude and the relative standard deviation (R.S.D.) of repeatability at the 5 μg ml −1 level were all below 15%. Furthermore, in this study, the influences of IMS cell temperature on the ion mobility spectra of these compounds were investigated.

Chemical standards in ion mobility spectrometry

Positive ion mobility spectra for three compounds (2,4-dimethylpyridine (2,4-DMP, commonly called 2,4-lutidine), dimethyl methylphosphonate (DMMP) and 2,6-di- t-butyl pyridine (2,6-D tBP)) have been studied in air at ambient pressure over the temperature range 37–250 °C with (H 2O) n H + as the reactant ion. All three compounds yield a protonated molecule but only 2,4-dimethylpyridine and dimethyl methylphosphonate produced proton-bound dimers. The reduced mobilities ( K 0) of protonated molecules for 2,4-dimethylpyridine and DMMP increase significantly with increasing temperature over the whole temperature range indicating changes in ion composition or interactions; however, K 0 for the protonated molecule of 2,6-di- t-butyl pyridine was almost invariant with temperature. The K 0 values for the proton-bound dimers of 2,4-dimethylpyridine and DMMP also showed little dependence on temperature, but could be obtained only over an experimentally smaller and lower temperature range and at elevated concentrations. Chemical standards will be helpful as mobility spectra from laboratories worldwide are compared with increased precision and 2,6-di- t-butyl pyridine may be a suitable compound for use in standardizing reduced mobilities. The effect of thermal expansion of the drift tube length on the calculation of reduced mobilities is emphasized.

Regularized Linear Discriminant Analysis of Wavelet Compressed Ion Mobility Spectra

Wavelet compression (WC) coupled to a regularized version of linear discriminant analysis (LDA) was evaluated as an effective classifier for identification of benzene, toluene, ethyl benzene, and the xylene isomers (BTEX) from their positive ion mobility spectra. A novel LDA classifier was devised that uses pseudoinverses of the within-group covariance matrices. The pseudoinverse allows LDA to be applied directly to underdetermined data. Wavelet compression improved the classification by removing noise from the spectra. Spectra compressed with the daublet 22 filter yielded better prediction than data compressed by principal components. Ion mobility spectrometry (IMS) affords rapid and sensitive measurements that may be used for process monitoring. This study demonstrates that classification by LDA directly on the wavelet-compressed (WTLDA) positive ion spectra can be used for identification of BTEX compounds. The accompanying benefits include fast model building, removal of noise, and improved classification. Benzene, toluene, ethyl benzene, and o-, m-, and p-xylene at high and low concentrations were used to construct the classification models. Spectra from intermediate concentrations were used for evaluation. Optimization of prediction favored shorter wavelet filters than those obtained from filters optimized for reconstruction.

Gas-Phase Ion Mobility Studies of Amines and Polyether/Amine Complexes Using Tandem Quadrupole Ion Trap/Ion Mobility Spectrometry

The gas-phase positive ion mobility spectra of isomeric amines and polyether/amine complexes have been measured using a tandem quadrupole ion trap/ion mobility spectrometer. Ion mobilities of isomeric amines in helium, determined relative to benzene at pressures in the range 1–2 Torr, vary with the structure of the amine. The ability of quadrupole ion trap/ion mobility spectrometry to differentiate between a pharmacologically-active substance and an associated isomeric amine is demonstrated. Non-covalent complexes of cyclic and acyclic polyethers with protonated amines were generated by ion/molecule reactions in the ion trap and analysed by ion mobility spectrometry. The ion mobilities in helium may be interpreted in terms of the preferred conformations for these complexes. The use of polyether hosts as shift compounds for enhancing the relative mobilities of small amine guest ions is proposed.

Corona discharge ion mobility spectrometry of aliphatic and aromatic hydrocarbons

Positive ion mobility spectra of n-alkanes ( n-C 5 to n-C 19), branched chain alkanes (C 5 to C 9) and aromatic compounds (benzene and alkylated benzenes) were acquired with an ion mobility spectrometer equipped with a corona discharge ionization source. Reduced mobilities and mass-to-mobility correlation curves were determined for these compounds. Depending on their concentration, the n-alkanes form one or two product ion peaks. The mobilities of product ion peaks regularly decrease with increasing chain length. The same behavior was observed for branched chain alkanes. However, characteristic fragment ions are additionally formed in comparison with n-alkanes. The investigated aromatic hydrocarbons show simple spectra consisting of up to three characteristic product ion peaks. The obtained mass-to-mobility correlation curve differs from that determined using photoionization.

Ion mobility spectra of selected amines and their application in field testing with the use of a portable IMS device

The positive ion mobility spectra of selected amines, N,N-diethyl-p-toluidine, N,N-dimethyl-1-naphth-ylamine, N-napthyl-ethylenediamine, ethanolamine, n-heptylamine, and 2-isopropylaniline were measured with a portable IMS device with lutidine (2,4-dimethyl-pyridine) as the reference compound. The reduced mobilities of the above-mentioned amines were found to be 1.62, 1.60, 2.26, 2.29, 1.51, 1.69 cm2 V−1 s−1, respectively, and did not vary with different background gases. These amines were compared with several other amines in the literature, and the results of different mobility values of similar amines were explained. The minimum detection limits of N,N-diethyl-p-toluidine, N,N-dimethyl-1-naphth- ylamine, and N-naphthyl-ethylenediamine were measured to be 0.05, 0.1, and 30 ppb, respectively. The response curve for N,N-diethyl-p-toluidine was nearly linear in the range from 50 to 110 ppb. The response curve for N,N-dimethyl-1-naphthylamine was nearly linear in the range from 30 to 100 ppb. In this article the IMS spectra of background gases, lutidine, and mixtures of amines with three extraction solvents are measured and analyzed. Selective detection of amines achieved by doping NH3, ethanol, acetone, and ether into a dilute concentration of amines in air is also discussed. Finally, the results of field tests in a chemical plant are presented. © 1997 John Wiley & Sons, Inc.

Ion mobility spectra of selected amines and their application in field testing with the use of a portable IMS device

The positive ion mobility spectra of selected amines, N,N-diethyl-p-toluidine, N,N-dimethyl-1-naphthylamine, N-napthyl-ethylenediamine, ethanolamine, n-heptylamine, and 2-isopropylaniline were measured with a portable IMS device with lutidine (2,4-dimethyl-pyridine) as the reference compound. The reduced mobilities of the above-mentioned amines were found to be 1.62, 1.60, 2.26, 2.29, 1.51, 1.69 cm(2) V-1 s(-1), respectively, and did not vary with different background gases. These amines were compared with several other amines in the literature, and the results of different mobility values of similar amines were explained. The minimum detection limits of N,N-diethyl-p-toluidine, N,N-dimethyl-1-naphthylamine, and N-naphthyl-ethylenediamine were measured to be 0.05, 0.1, and 30 ppb, respectively. The response curve for N,N-diethyl-p-toluidine was nearly linear in the range from 50 to 110 ppb. The response curve for N,N-dimethyl-1-naphthylamine was nearly linear in the range from 30 to 100 ppb. In this article the IMS spectra of background gases, lutidine, and mixtures of amines with three extraction solvents are measured and analyzed. Selective detection of amines achieved by doping NH3, ethanol, acetone, and ether into a dilute concentration of amines in air is also discussed. Finally, the results of field tests in a chemical plant are presented. (C) 1997 John Wiley & Sons, Inc.

Evaluation of gas chromatography coupled with ion mobility spectrometry for monitoring vinyl chloride and other chlorinated and aromatic compounds in air samples

AbstractThe objective of this research was to evaluate, in the laboratory, the potential of gas chromatography/ion mobility spectrometry (GC/IMS) for monitoring vinyl chloride and other organic compounds in air samples in the field. It was determined that GC/IMS has the potential to directly detect vinyl chloride in air at the 2 ppbv level, and when concentrated on an adsorbent trap from a 1 L sample of air, detection could be lowered to the 0.02 ppbv level. From a comparative investigation of 18 EPA priority pollutants and 34 common vapor‐phase organic compounds, many compounds were found to provide a more sensitive response in IMS than vinyl chloride, indicating that GC/IMS would be broadly applicable to the direct detection of vapor‐phase organics in air.Operating parameters including drift gas, spectrometer temperature, and sample‐inlet position were evaluated and discussed with respect to sensitivity and resolution. High temperature dramatically increased sensitivity to vinyl chloride. Vinyl chloride was shown to produce both negative and positive ion mobility spectra, with the negative‐mode spectra resulting from electron‐capture dissociation of the vinyl chloride. The limit of detection for vinyl chloride was found to be 7 pg/s. Limits of detection for 18 EPA priority pollutants were determined and compared to vinyl chloride. The responses of 34 other vapor‐phase organic compounds were also compared to that of vinyl chloride. Non‐selective, positive‐ion detection of 30 of the 34 compounds was demonstrated along with selective, electron‐capture‐type detection of 29 of them. Chloride‐specific and bromide‐specific detection illustrated the advantages of selected‐ion monitoring in IMS.

Atmospheric ion mobility spectra near the ground

The mobility spectra of positive and negative ions artificially produced in the ambient air near the ground were measured by using a newly constructed mobility spectrometer having parallel plate electrodes. The negative mobility spectra obtained by this spectrometer have a very sharp peak at 1.80 cm 2 volt −1 s −1, and the average negative ion mobility is estimated to be 2.40 cm 2 volt −1 s −1. In the positive ion mobility spectra, on the other hand, a rather broad peak is seen at 1.25 cm 2 volt −1 s −1. The average positive ion mobility is estimated to be 1.69 cm 2 volt −1 s −1. By comparing the result with recent mass spectrometric measurements and a model calculation, detailed discussions are given. Additional experiments were made to test for changes of the mobility spectra by using nitric acid and ammonia vapours, and gases in tobacco smoke.

Sensing of Petrochemical Fuels in Soils Using Headspace Analysis with Photoionization-Ion Mobility Spectrometry

Abstract Photoionization-Ion Mobility Spectrometry (PI-IMS) was used to distinguish among common petrochemical fuels including leaded gasoline, unleaded gasoline, kerosene, and diesel fuel through sampling of headpsace vapors over liquid samples. Positive ion mobility spectra obtained in air at ambient pressure were comprised of 3 to 5 peaks which were tentatively identified as benzene, alkylated benzenes, naphthalene and alkylated naphthalenes. The simple mobility spectra from PI-IMS analysis, due to selective ionization of aromatic hydrocarbons. were contrasted with the complex chromatographic patterns for the same fuels from scanning GC/MS analysis. Discrimination between unleaded gasoline and diesel fuel in fuel mixtures was possible using PI-IMS across a broad range of gas-phase concentration ratios. Fuels were also detected in soil using PI-IMS analysis of headspace vapors at 25[ddot]C. Unleaded gasoline in soil was detected from 0.16 to 16 mg/kg for only 0.1 g of sample with nearly linear response. Reproducibility in preparation and analysis of soil samples was 10 to 60% RSD for individual components while instrumental PI-IMS reproducibility with toluene alone was 5% RSD. Water vapor had no effect on PI-IMS response for fuel vapors alone, but increased moisture content in soils caused enhanced response. Drilling mud from a natural gas reserve pit was used to demonstrate environmental application of PI-IMS in sensing a water-saturated sample. Qualitative inspection of results showed no serious complication to PI-IMS response from water. Effects on sensor sensitivity from weathering and other environmental alterations of fuels in soils and groundwater were not explored.