Ion Mobility Spectrometry Spectra Research Articles

Radial basis function neural network optimization algorithm based on dynamic inertial weight particle swarm optimization for separating overlapping peaks in ion mobility spectrometry.

Ion mobility spectrometry (IMS), as a promising analytical tool, has been widely employed in the structural characterization of biomolecules. Nevertheless, the inherent limitation in the structural resolution of IMS frequently results in peak overlap during the analysis of isomers exhibiting comparable structures. The radial basis function (RBF) neural network optimization algorithm based on dynamic inertial weight particle swarm optimization (DIWPSO) was proposed for separating overlapping peaks in IMS. The RBF network structure and parameters were optimized using the DIWPSO algorithm. By extensively training using a large dataset, an adaptive model was developed to effectively separate overlapping peaks in IMS data. This approach successfully overcomes issues related to local optima, ensuring efficient and precise separation of overlapping peaks. The method's performance was evaluated using experimental validation and analysis of overlapping peaks in the IMS spectra of two sets of isomers: 3'/6'-sialyllactose; fructose-6-phosphate, glucose-1-phosphate, and glucose-6-phosphate. A comparative analysis was conducted using other algorithms, including the sparrow search algorithm, DIWPSO algorithm, and multi-objective dynamic teaching-learning-based optimization algorithm. The comparison results show that the DIWPSO-RBF algorithm achieved remarkably low maximum relative errors of only 0.42%, 0.092%, and 0.41% for ion height, mobility, and half peak width, respectively. These error rates are significantly lower than those obtained using the other three algorithms. The experimental results convincingly demonstrate that this method can adaptively, rapidly, and accurately separate overlapping peaks of multiple components, improving the structural resolution of IMS.

A non-invasive and rapid method for discrimination of inkjet printouts by ion mobility spectrometry combined with chemometrics

The identification and differentiation of inkjet printouts can be important to establish the authenticity of questioned documents during judicial processes. In this work, we developed an analytical method based on ion mobility spectrometry (IMS) combined with chemometrics to identify inkjet printouts for rapid on-site detection. The characteristic peaks in IMS spectra were first identified by HS–GC–MS which showed the chemical differences between inkjet printouts. To achieve further differentiation of the inkjet printouts, principal component analysis (PCA) was performed. The results demonstrated that they can grouped based on the types of inks used, regardless of the printer type and the aging time of the document. For accurate discrimination of inkjet printed documents, a supervised model based on orthogonal partial least square discriminant analysis (OPLS-DA) was developed, which provided good quality (R2Y = 0.954, Q2 = 0.953). The model gave excellent accuracy by correctly classifying 99.37% of the validation set (159 samples). Furthermore, the partial least squares (PLS) models were applied to predict the formation time of documents. A combination of Orthogonal signal correction (OCS) combined and discrete wavelet transform (DWT) was used for data processing showing the best performance for the PLS model. It provided satisfactory predictions for inkjet printouts over 7-1446 days aging time. IMS combined with chemometrics was confirmed to be feasible and accurate for questioned documents identification and can be further applied in solving actual cases.

Comparison of the positive and negative modes of corona discharge ion source for direct determination of aspirin in urine by ion mobility spectrometry

Ionization of aspirin (A) in positive and negative modes of a corona discharge (CD) ion source was studied by ion mobility spectrometry (IMS). The IMS spectra showed that aspirin can be both protonated, AH+, and deprotonated, (A-H)-, in positive and negative modes of CD, respectively. Using DFT calculations, it was found that the carbonyl oxygen of COOH group is the most preferred site of protonation with proton affinity of 867.8 kJ mol-1. Also, the calculated ΔG values for deprotonation of aspirin by O2- and O3- were -71.2 and -28.5 kJ mol-1, respectively, indicating its deprotonation is thermodynamically possible. Hydration of AH+ and (A-H)- was studied theoretically and it was found that AH+ and AH+(H2O) are the most abundant species in the ionization region in the presence of 40 ppm of water vapor at 100–200 °C, while (A-H)- is not hydrated in the same condition. The results of measurements in urine showed that urea content of urine interferes with detection of aspirin in positive CD, while urea was not ionized in the negative CD so that aspirin was determined in urine with recovery of 94% in negative CD.

The influence of different types of reactant ions on the ionization behavior of polycyclic aromatic hydrocarbons in corona discharge ion mobility spectrometry

Some polycyclic aromatic hydrocarbons (PAHs) are considered to be cancer-causing chemicals, and ion mobility spectrometry (IMS) is used for on-site detection of such hazardous chemicals. In IMS, the ionization behavior of analytes is affected by the types of reactant ions (RIs). In the present work, the influence of different types of RIs on the ionization behaviors of PAHs in an ion mobility spectrometer equipped with a corona discharge ionization source was investigated using various RIs. Selected PAHs were dissolved in anisole, fluorobenzene, chlorobenzene, or bromobenzene. The IMS analysis procedure was performed as follows: (a) the PAH solution was dropped onto the smear matrix; (b) the smear matrix was immediately inserted into the sample inlet to minimize evaporation of the solvent; and (c) the IMS analysis was performed. The lowest amount studied was 10 ng. Variations in the IMS spectra with time were investigated. PAHs were not ionized by RIs of protonated molecules ([M + H]+ ) such as air/moisture and acetone, but they were ionized by charge transfer reactions with RIs of molecular ions (M•+ ) of solvents such as anisole, fluorobenzene, chlorobenzene, and bromobenzene. The PAH ions were detected following a time delay of ~1-5 s after the sample introduction, and the times at which the maximum intensities for the PAHs were observed were different. The detection limits of PAHs in chlorobenzene were on the whole better than those in other solvents, whereas those in fluorobenzene were worse. The detection limits of pyrene and benzo[a]anthracene were better than those of the other PAHs irrespective of the solvent used. PAH molecules were ionized by charge transfer reactions with RIs of the solvents, and their ions were detected ~1-5 s after sample introduction. The order of the ionization efficiency was chlorobenzene > anisole > bromobenzene > fluorobenzene.

Atmospheric Pressure Chemical Ionisation study of selected Volatile Organic Compounds (VOCs) by Ion Mobility Spectrometry coupled with orthogonal acceleration Time Of Flight Mass Spectrometry

In this work, we present an Atmospheric Pressure Chemical Ionisation (APCI) study of several organic solvents relevant to Thin Layer Chromatography (TLC) (methanol, ethanol, propan-2-ol, acetone, ethyl acetate, diethylamine). The solvents were investigated using an Ion Mobility Spectrometry (IMS) combined with orthogonal acceleration Time Of Flight Mass Spectrometry (IMS-oaTOF MS). The solvents were iononised by Reactant Ions (RI – H+.(H2O)3,4 m/z 55 and 73). The ions were analysed using IMS and IMS-oaTOF technique was used to assign the ion mobility peaks to ions according to their m/z. IMS spectra of methanol, ethanol, propan-2-ol and diethylamine exhibited only one peak (reduced ion mobilities of 2.19, 2.07, 1.98, 2.06 cm2s−1V−1 respectively) whereas acetone and ethyl acetate were characterised by two peaks (2.15, 1.85 and 1.94, 1.53 cm2s−1V−1 respectively). The IMS-oaTOF spectrometry assigned IMS peaks of VOCs to M⋅H+(H2O)n. n = 0,1,2 or M2⋅H+ ions, where M represents the solvent molecule.

Structurally Informative Isotopic Shifts in Ion Mobility Spectra for Heavier Species.

The isotopic molecular envelopes due to stable isotopes for most elements were a staple of mass spectrometry since its origins, often leveraged to identify and quantify compounds. However, all isomers share one MS envelope. As the molecular motion in media also depends on the isotopic composition, separations such as liquid chromatography (LC) and ion mobility spectrometry (IMS) must also feature isotopic envelopes. These were largely not observed because of limited resolution, except for the (structurally uninformative) shifts in LC upon H/D exchange. We recently found the isotopic shifts in FAIMS for small haloanilines (∼130-170 Da) to hinge on the halogen position, opening a novel route to isomer characterization. Here, we extend the capability to heavier species: dibromoanilines (DBAs, ∼250 Da) and tribromoanilines (TBAs, ∼330 Da). The 13C shifts for DBAs and TBAs vary across isomers, some changing sign. While 81Br shifts are less specific, the 2-D 13C/81Br shifts unequivocally differentiate all isomers. The trends for DBAs track those for dichloroanilines, with the 13C shift order preserved for most isomers. The peak broadening due to merged isotopomers is also isomer-specific. The absolute shifts for TBAs are smaller than those for lighter haloanilines, but differentiate isomers as well because of compressed uncertainties. These results showcase the feasibility of broadly distinguishing isomers in the more topical ∼200-300 Da range using the isotopic shifts in IMS spectra.

Fast quantification of whisky lactone in oak wood by ion mobility spectrometer

An Ion Mobility Spectrometry (IMS) apparatus has been used to detect the β-methyl-γ-octalactone (Whisky Lactone – WL) standard in the air and as well WL vapours originating from the oak wood samples. The IMS was equipped with Atmospheric Pressure Chemical Ionisation (APCI) ion source based on a Corona Discharge (CD) and was operated in the positive polarity. The IMS spectrum of WL exhibits two peaks, a monomer with reduced ion mobility value K0 = 1.39 cm2V−1s−1 and dimer K0 = 1.09 cm2V−1s−1. Using Ion Mobility orthogonal acceleration Time of Flight mass spectrometer (IMS-oaTOF MS) these peaks were identified as protonated monomer M.H+.(H2O)0,1 and dimer M2.H+ ions respectively. The limit of detection study resulted in LOD for WL of 50 ppbv. Detection of WL from oak wood samples of different “Quality Level” (QL) categories (categories 1 to 10), indicated strong correlation between the QL category number and the response of the IMS.

Buffer gas additives (modifiers/shift reagents) in ion mobility spectrometry: Applications, predictions of mobility shifts, and influence of interaction energy and structure.

Ion mobility spectrometry (IMS) is an analytical technique used for fast and sensitive detection of illegal substances in customs and airports, diagnosis of diseases through detection of metabolites in breath, fundamental studies in physics and chemistry, space exploration, and many more applications. Ion mobility spectrometry separates ions in the gas-phase drifting under an electric field according to their size to charge ratio. Ion mobility spectrometry disadvantages are false positives that delay transportation, compromise patient's health and other negative issues when IMS is used for detection. To prevent false positives, IMS measures the ion mobilities in 2 different conditions, in pure buffer gas or when shift reagents (SRs) are introduced in this gas, providing 2 different characteristic properties of the ion and increasing the chances of right identification. Mobility shifts with the introduction of SRs in the buffer gas are due to clustering of analyte ions with SRs. Effective SRs are polar volatile compounds with free electron pairs with a tendency to form clusters with the analyte ion. Formation of clusters is favored by formation of stable analyte ion-SR hydrogen bonds, high analytes' proton affinity, and low steric hindrance in the ion charge while stabilization of ion charge by resonance may disfavor it. Inductive effects and the number of adduction sites also affect cluster formation. The prediction of IMS separations of overlapping peaks is important because it simplifies a trial and error procedure. Doping experiments to simplify IMS spectra by changing the ion-analyte reactions forming the so-called alternative reactant ions are not considered in this review and techniques other than drift tube IMS are marginally covered.

Development of a plug-type IMS-MS instrument and its applications in resolving problems existing in in-situ detection of illicit drugs and explosives by IMS

Ion mobility spectrometry (IMS) which acts as a rapid analysis technique is widely used in the field detection of illicit drugs and explosives. Due to limited separation abilities of the pint-sized IMS challenges and problems still exist regarding high false positive and false negative responses due to the interference of the matrix. In addition, the gas-phase ion chemistry and special phenomena in the IMS spectra, such one substance showing two peaks, were not identified unambiguously. In order to explain or resolve these questions, in this paper, an ion mobility spectrometry was coupled to a mass spectrometry (IMS-MS). A commercial IMS is embedded in a custom-built ion chamber shell was attached to the mass spectrometer. The faraday plate of IMS was fabricated with a hole for the ions to passing through to the mass spectrometer. The ion transmission efficiency of IMS-MS was optimized by optimizing the various parameters, especially the distance between the faraday plate and the cone of mass spectrum. This design keeps the integrity of the two original instruments and the mass spectrometry still works with multimode ionization source (i.e., IMS-MS, ESI-MS, APCI-MS modes). The illicit drugs and explosive samples were analyzed by the IMS-MS with 63Ni source. The results showed that the IMS-MS is of high sensitivity. The ionization mechanism of the illicit drug and explosive samples with 63Ni source were systematically studied. In addition, the interferent which interfered the detection of cocaine was identified as dibutyl phthalate (DBP) by this platform. The reason why the acetone solution of amphetamine showed two peaks was explained.

Caffeine and glucosamine mobility shifts by adduction with 2-butanol depended on interaction energy, charge delocalization, and steric hindrance in ion mobility spectrometry.

Ion mobility spectrometry (IMS) is an analytical technique that separates gas-phase ions drifting under an electric field according to their size to charge ratio. We used electrospray ionization-drift tube IMS coupled to quadrupole mass spectrometry to measure the mobilities of glucosamine (GH+ ) and caffeine (CH+ ) ions in pure nitrogen or when the shift reagent (SR) 2-butanol was introduced in the drift gas at 6.9mmol m-3 . Binding energies of 2-butanol-ion adducts were calculated using Gaussian 09 at the CAMB3LYP/6-311++G(d,p) level of theory. The mobility shifts with the introduction of 2-butanol in the drift gas were -2.4% (GH+ ) and -1.7% (CH+ ) and were due to clustering of GH+ and CH+ with 2-butanol. The formation of GBH+ was favored over that of CBH+ because GBH+ formed more stable hydrogen bonds (83.3kJ/mol) than CBH+ (81.7kJ/mol) for the reason that the positive charge on CH+ is less sterically available than on GH+ and the charge is stabilized by resonance in CH+ . These results are a confirmation of the arguments used to explain the drift behavior of these ions when ethyl lactate SR was used (Bull Kor Chem Soc 2014, 1023-1028). This study is a step forward to predict IMS separations of overlapping peaks in IMS spectra, simplifying a procedure that is trial and error by now.

Ion Mobility Spectrometry of Heavy Metals.

A simple, fast, and inexpensive method was developed for detecting heavy metals via the ion mobility spectrometry (IMS) in the negative mode. In this method, Cl(-) ion produced by the thermal ionization of NaCl is employed as the dopant or the ionizing reagent to ionize heavy metals. In practice, a solution of mixed heavy metals and NaCl salts was directly deposited on a Nichrome filament and electrically heated to vaporize the salts. This produced the IMS spectra of several heavy-metal salts, including CdCl2, ZnSO4, NiCl2, HgSO4, HgCl2, PbI2, and Pb(Ac)2. For each heavy metal (M), one or two major peaks were observed, which were attributed to M·Cl(-) or [M·NaCl]Cl(-)complexes. The method proved to be useful for the analysis of mixed heavy metals. The absolute detection limits measured for ZnSO4 and HgSO4 were 0.1 and 0.05 μg, respectively.

Determination of 3,4-methylenedioxypyrovalerone (MDPV) in oral and nasal fluids by ion mobility spectrometry

A fast and sensitive methodology has been developed for the evaluation of the 3,4-methylenedioxypyrovalerone (MDPV) consumed. Based on ion mobility spectrometry (IMS), MDPV was directly determined in nasal fluids with a limit of detection (LOD) in the order of 22 ng mL(-1), which corresponds to an absolute amount of 33 ng of MDPV per swab. MDPV was also determined after liquid-liquid microextraction (LLME) in oral fluids to avoid matrix effects, obtaining a LOD value of 4.4 ng mL(-1) in oral fluid samples. The IMS spectrum for MDPV exhibited a peak with K0 = 1.210 ± 0.005 cm(2)V(-1) s(-1) at a drift time of 14.62 ms, the total analysis time being 4.5 min per oral fluid and 1.5 min per nasal fluid sample. Samples must be analyzed within 24 h following collection and dissolution in 2-propanol, based on the complementary stability studies.

Experimental and theoretical study of the kinetic of proton transfer reaction by ion mobility spectrometry

Rate constants of the proton transfer reactions RH++DMP→R+DMP·H+, where R was acetone (Ac), trimethyl amine (TMA) or H2O and DMP was 2,4-dimethyl pyridine have been measured by ion mobility spectrometry (IMS). The Reactant R was injected into the ionization region of IMS to produce RH+ while DMP was continuously delivered to the drift region to react with the RH+ pulsed into the drift tube by a shutter grid. Since DMP.H+ was generated along the drift tube, a tail appeared in the IMS spectrum that contained kinetic information. To prevent proton-bound dimer formation, the reactions were carried out at elevated temperatures (170–230°C). We measured rate constants of 1.17×10−9, 0.90×10−9 and 0.68×10−9cm3s−1 for proton transfer from H3O+, Ac·H+ and TMA·H+ to DMP, respectively. The experimental rate constants were almost temperature independent, indicating that no activation energy was involved in those proton transfer reactions. The rate constants were also calculated by using average dipole orientation (ADO) theory at B3LYP and MP2 levels. The calculated values revealed acceptable agreement between the experimental and theoretical trends.

Quantitative information in decay curves obtained with a pulsed ion mobility spectrometer

Ion mobility spectrometry (IMS) is well known for its very high sensitivity, and thus IMS spectra are commonly used in the identification of trace gases. Extracting quantitative information from IMS spectra is, in contrast, difficult, especially regarding the reproducibility due to the nature of the processes involved in the measurement of the spectra. Here we present data extracted from signal decay curves obtained with a pulsed IMS, which can support the determination of substance concentrations in the lower ppb range with good stability.

Rapid detection of sepsis in rats through volatile organic compounds in breath

Background Sepsis is one of the main causes of death in adult intensive care units. The major drawbacks of the different methods used for its diagnosis and monitoring are their inability to provide fast responses and unsuitability for bedside use. In this study, performed using a rat sepsis model, we evaluate breath analysis with Ion Mobility Spectrometry (IMS) as a fast, portable and non-invasive strategy. Methods This study was carried out on 20 Sprague-Dawley rats. Ten rats were injected with lipopolysaccharide from Escherichia coli and ten rats were IP injected with regular saline. After a 24-h period, the rats were anaesthetized and their exhaled breaths were collected and measured with IMS and SPME-gas chromatography/mass spectrometry (SPME-GC/MS) and the data were analyzed with multivariate data processing techniques. Results The SPME-GC/MS dataset processing showed 92% accuracy in the discrimination between the two groups, with a confidence interval of between 90.9% and 92.9%. Percentages for sensitivity and specificity were 98% (97.5–98.5%) and 85% (84.6–87.6%), respectively. The IMS database processing generated an accuracy of 99.8% (99.7–99.9%), a specificity of 99.6% (99.5–99.7%) and a sensitivity of 99.9% (99.8–100%). Conclusions IMS involving fast analysis times, minimum sample handling and portable instrumentation can be an alternative for continuous bedside monitoring. IMS spectra require data processing with proper statistical models for the technique to be used as an alternative to other methods. These animal model results suggest that exhaled breath can be used as a point-of-care tool for the diagnosis and monitoring of sepsis.

Transitions between elongated conformations of ubiquitin [M+11H]11+ enhance hydrogen/deuterium exchange.

Hydrogen/deuterium (H/D) exchange reactions between different elongated conformations of [M + 11H](11+) ions of ubiquitin and D(2)O are studied by a combination of ion mobility spectrometry (IMS) and mass spectrometry techniques. Three conformers (B, C, and D), resolved in the IMS separation, each exchange ∼27 hydrogens upon exposure to 0.06 Torr of D(2)O vapor for ∼35 to 40 ms. However, a region of the IMS spectrum that appears between the C and D states (corresponding to ions that undergo a structural transition during the mobility separation) undergoes substantially more exchanges (∼39 total sites, 44% more than the B, C, and D states). Selection and activation of the individual B, C, and D states reveals that the increased H/D exchange occurs during the transition between structures. Overall, these studies suggest a key process in establishing the maximum exchange levels involves structural transitions, which allow protected sites to be exposed for some fraction of the reaction time. Analysis of changes in exchange levels upon structural transitions can provide insight about common regions of structure that exist in the B, C, and D conformations.

Investigation of gaseous metabolites from moulds by Ion Mobility Spectrometry (IMS) and Gas Chromatography-Mass Spectrometry (GC-MS)

The metabolism of moulds results in the formation of various microbial volatile organic compounds (MVOCs). These substances can be used as an indicator for the presence of moulds in the indoor environment. Three different mould strains were cultivated on culture media and IMS spectra of gaseous mould metabolites were recorded using a portable mini system with a tritium source and a 5 cm drift cell. The headspace spectra are characteristic for mould species and their age. Typical gaseous components of the metabolites were identified and compared with results obtained from gas chromatography using a mass spectrometer detector. It was observed that the MVOCs formation depends on mould species and their growing stage with a maximum of MVOCs emission occurring during the first 10 days. These preliminary results show that IMS can be applied to detect MVOCs in indoor environment and indicate hidden mould growth.

Monte Carlo simulation of ion transport in ion mobility spectrometry

A program for simulation of ion trajectories in ion mobility spectrometry (IMS) instruments has been developed and incorporated into SIMION 7.0 [Int. J. Mass Spectrom. 200 (2000) 3–25]. Simulations were based on elastic collisions between ions and gas particles and conducted for an IMS drift tube. The program was validated by comparing the reduced mobility of helium ions derived from the simulation with the experimental data for helium ions in neon drift gas in low electric fields. Typical IMS parameters, including pressure, temperature, and flow rate of the drift gas were taken into account in the simulations. The program demonstrates capabilities of generating IMS spectra and predicting ion transport efficiency and separating ions. For the IMS drift tube studied, a correlation between imperfection of the electric field distribution and low resolution has been observed.

Distortion of Ion Structures by Field Asymmetric Waveform Ion Mobility Spectrometry

Field asymmetric waveform ion mobility spectrometry (FAIMS) is emerging as a major analytical tool, especially in conjunction with mass spectrometry (MS), conventional ion mobility spectrometry (IMS), or both. In particular, FAIMS is used to separate protein or peptide conformers prior to characterization by IMS, MS/MS, or H/D exchange. High electric fields in FAIMS induce ion heating, previously estimated at <10 degrees C on average and believed too weak to affect ion geometries. Here we use a FAIMS/IMS/MS system to compare the IMS spectra for ESI-generated ubiquitin ions that have and have not passed FAIMS and find that some unfolding occurs for most charge states. These data and their comparison with the reported protein unfolding in a Paul trap imply that at least some structural transitions observed in FAIMS, or previously in an ion trap, are not spontaneous. The observed unfolding is similar to that produced by heating of approximately 50 degrees C above room temperature, consistent with the calculated heating of ions at FAIMS waveform peaks. Hence, the ion isomerization in FAIMS likely proceeds in steps during the "hot" periods, especially right after entering the device. The process distorts ion geometries and causes ion losses by a "self-cleaning" mechanism and thus should be suppressed as much as possible. We propose achieving that via cooling FAIMS by the amount of ion heating; in most cases, cooling by approximately 75 degrees C should suffice.

A New Method for Measuring the Diffusion Coefficient in a Gas Phase

A new and fast method for measuring the diffusion coefficients of binary gas mixtures using ion mobility spectrometry (IMS) has been developed. In this method, the sample is injected as a short pulse into the flowing drift gas, forming a Gaussian concentration profile inside the drift region. This Gaussian cloud is irradiated with a fast moving swarm of electrons to create negative ions. The flash of electrons is so short that the negative ions do not move much during the exposure time. The ions then drift toward the detector, where they are collected. The collected ion signal pattern reflects the spatial distribution of the sample inside the cloud at the time of exposure. This is repeated in intervals of 300-400 ms to monitor the spatial spreading of the molecules in the drift region. Consecutive IMS spectra show the evolution of the cloud over time. The collected spectra are fit to Gaussian functions to extract diffusion coefficients. Using this method, the diffusion coefficient of O(2), CHCl(3), and C(2)H(2)Cl(2) were measured, and the results are in good agreement with the previously reported experimental data.