A review of recent, unconventional applications of ion mobility spectrometry (IMS)

Characterization of the flavor profile of Hulatang using GC-IMS coupled with sensory analysis

Background

Hulatang is a traditional specialty snack in Henan, China, and is well known for its unique flavor.

Methods

In this study, the volatile organic compounds (VOCs) in four kinds of Hulatang from two representative regions in Henan Province (Xiaoyaozhen and Beiwudu) were evaluated using headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS).

Results

The results showed that Xiaoyaozhen Hulatang exhibited more ethers, fewer terpenes and ketones than Beiwudu Hulatang. Additionally, Hulatang from different regions were classified using the orthogonal partial least squares-discriminant analysis (OPLS-DA) based on GC-IMS data. Twenty aroma substances were selected as the potential markers using the variable importance in the projection (VIP) variable selection method. Additionally, fifteen aroma components significantly contributing to the aroma of Hulatang were screened using the relative odor activity value (ROAV) (ROAV > 1). Combined with the sensory score results, twelve key substances with significant correlation with odor perception were selected. The flavor characteristics of the key substances revealed that the flavor of Hulatang was mainly composed of volatile components with camphor, green, almond, fatty, spicy, herbal, vegetable, fruity, floral, musty, and solvent aromas.

Conclusion

Overall, the experimental results provide a theoretical basis for evaluating the flavor characteristics of Hulatang from different regions using GC-IMS.

Computational tools and algorithms for ion mobility spectrometry-mass spectrometry

Ion mobility spectrometry-mass spectrometry (IMS-MS or IM-MS) is a powerful analytical technique that combines the gas-phase separation capabilities of IM with the identification and quantification capabilities of MS. IM-MS can differentiate molecules with indistinguishable masses but different structures (e.g., isomers, isobars, molecular classes, and contaminant ions). The importance of this analytical technique is reflected by a staged increase in the number of applications for molecular characterization across a variety of fields, from different MS-based omics (proteomics, metabolomics, lipidomics, etc.) to the structural characterization of glycans, organic matter, proteins, and macromolecular complexes. With the increasing application of IM-MS there is a pressing need for effective and accessible computational tools. This article presents an overview of the most recent free and open-source software tools specifically tailored for the analysis and interpretation of data derived from IM-MS instrumentation. This review enumerates these tools and outlines their main algorithmic approaches, while highlighting representative applications across different fields. Finally, a discussion of current limitations and expectable improvements is presented.

Benchtop volatilomics supercharged: How machine learning based design of experiment helps optimizing untargeted GC-IMS gas phase metabolomics

Gas chromatography-ion mobility spectrometry (GC-IMS) plays a significant role in both targeted and non-targeted analyses. However, the non-linear behavior of IMS and its complex ion chemistry pose challenges for finding optimal experimental conditions using existing methodologies. To address these issues, integrating machine learning (ML) strategies offers a promising approach. In this study, we propose a hybrid strategy, combining design of experiment (DOE) and machine learning (ML) for optimizing GC-IMS conditions in non-targeted volatilomic/flavoromic analysis, with saffron volatiles as a case study. To begin, a rotatable circumscribed central composite design (CCD) is used to define five influential GC-IMS factors of sample amount, headspace temperature, incubation time, injection volume, and split ratio. Subsequently, two ML models are utilized: multiple linear regression (MLR) as a linear model and Bayesian regularized-artificial neural network (BR-ANN) as a nonlinear model. These models are employed to predict the response variables of total peak areas (PAs) and the number of detected peaks (PNs) in GC-IMS. The findings show that there is a direct correlation between the factors in GC-IMS and the PNs, suggesting that MLR is a suitable approach for building a model in this scenario. However, the PAs exhibit nonlinear behavior, suggesting that BR-ANN is better suitable to capture this complexity. Notably, Derringer's desirability function is utilized to integrate the PAs and PNs, and in this scenario, MLR demonstrates satisfactory performance in modeling the GC-IMS factors.

Recent reports on the sensing strategy and the On-site detection of illegal drugs

In this review, works on the on-site detection of illegal drugs in recent years are summarised and discussed, most of which were published within the past five years. The detection methods are categorised as colourimetric, fluorescence, Raman spectrometry, ion mobility spectrometry, electrochemistry, and mass spectrometry. Also, strategies that are possibly suitable for on-site detection and the actual instrumentation to be used in the field are listed.

Charge transfer complex-based spectrophotometric analysis of famotidine in pure and pharmaceutical dosage forms

A straightforward and efficient spectrum technique was created using Ortho-chloranil as the electron acceptor (-acceptor) in a charge transfer (CT) complex formation reaction to determine the concentration of famotidine (FMD) in solutions. Compared to the double-distilled blank solution, the reaction result detected a definite violet colour at a maximum absorption wavelength of 546 nm, For concentrations range 2-28 µg/ml, the technique demonstrated excellent compliance with Beer-Law and Lambert's, as evidenced by its molar absorptivity of 2159.648 L mol-1 cm-1. Lower detection limits of 0.3024 µg/ml and 1.471 µg/ml, respectively, were discovered. The complexes of famotidine and Ortho-chloranil were found to have a 2:1 stoichiometry. Additionally, the suggested approach effectively estimated famotidine concentrations in pharmaceutical formulations, particularly in tablet form.

Test method for vapor collection and ion mobility detection of explosives with low vapor pressure

RATIONALE

Ion mobility spectrometry (IMS) has been widely used for on-site detection of explosives. Air sampling method is applicable only when the concentration of explosive vapor is considerably high in the air, but vapor pressures of common explosives such as 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), and pentaerythritol tetranitrate (PETN) are very low. A test method for analyzing the vapor detection efficiency of explosives with low vapor pressure via IMS was developed using artificial vapor and collection matrices.

METHODS

Artificial explosive vapor was produced by spraying an explosive solution in acetone. Fifteen collection matrices of various materials with woven or nonwoven structures were tested. Two arrangements of horizontal and vertical positions of the collection matrices were employed. Explosive vapor collected in the matrix was analyzed using IMS.

RESULTS

Only three collection matrices of stainless steel mesh (SSM), polytetrafluoroethylene sheet (PFS), and lens cleansing paper (LCP) showed the TNT and/or RDX ion peaks at an explosive vapor concentration of 49 ng/L. There was no collection matrix to detect PETN vapor at or lower than 49 ng/L. For the PFS, TNT and RDX were detected at a vapor concentration of 49 ng/L. For the LCP, TNT and RDX were detected at vapor concentrations of 14 and 49 ng/L, irrespectively.

CONCLUSIONS

The difference in the explosive vapor detection efficiencies could be explained by the adsorption and desorption capabilities of the collection matrices. The proposed method can be used for evaluating the vapor detection efficiency of hazardous materials with low vapor pressure.

Detection of Dimethyl Methyl Phosphonate by Silica Molecularly Imprinted Materials

In recent years, the increasing severity of chemical warfare agent threats to public safety has led to a growing demand for gas sensors capable of detecting these compounds. However, gas sensors used for the detection of chemical warfare agents must overcome limitations in sensitivity, selectivity, and reaction speed. This paper presents a sensitive material and a surface acoustic gas sensor for detecting dimethyl methyl phosphonate. The results demonstrate that the sensor exhibits good selectivity and could detect 80 ppb of dimethyl methyl phosphonate within 1 min. As an integral component of the sensor, the microstructure and adsorption mechanism of silica molecular imprinting material were studied in detail. The results show that the template molecule could significantly affect the pore volume, specific surface area, and hydroxyl density of mesoporous materials. These properties further affect the performance of the sensor. This study provides a valuable case study for the design of sensitive materials.

Airborne Pesticides-Deep Diving into Sampling and Analysis

The escalating utilization of pesticides has led to pronounced environmental contamination, posing a significant threat to agroecosystems. The extensive and persistent global application of these chemicals has been linked to a spectrum of acute and chronic human health concerns. This review paper focuses on the concentrations of airborne pesticides in both indoor and outdoor environments. The collection of diverse pesticide compounds from the atmosphere is examined, with a particular emphasis on active and passive air sampling techniques. Furthermore, a critical evaluation is conducted on the methodologies employed for the extraction and subsequent quantification of airborne pesticides. This analysis takes into consideration the complexities involved in ensuring accurate measurements, highlighting the advancements and limitations of current practices. By synthesizing these aspects, this review aims to foster a more comprehensive and informed comprehension of the intricate dynamics related to the presence and measurement of airborne pesticides. This, in turn, is poised to significantly contribute to the refinement of environmental monitoring strategies and the augmentation of precise risk assessments.

Formic Acid as a Dopant for Atmospheric Pressure Chemical Ionization for Negative Polarity of Ion Mobility Spectrometry and Mass Spectrometry

Formic acid (FA) is introduced as a potent dopant for atmospheric pressure chemical ionization (APCI) for ion mobility spectrometry (IMS) and mass spectrometry (MS). The mechanism of chemical ionization with the FA dopant was studied in the negative polarity using a corona discharge (CD)-IMS-MS technique in air. Standard reactant ions of the negative polarity present in air are O2-·(CO2)n·(H2O)m (m = 0, 1 and n = 1, 2) clusters. Introduction of the FA dopant resulted in the production of HCOO-·FA reactant ions. The effect of the FA dopant on the APCI of different classes of compounds was investigated, including plant hormones, pesticides, acidic drugs, and explosives. FA dopant APCI resulted in deprotonation and/or adduct ion formation, [M - H]- and [M + HCOO]-, respectively. Supporting density functional theory (DFT) calculations showed that the ionization mechanism depended on the gas-phase acidity of the compounds. FA dopant APCI led to the improvement of detection sensitivity, suppression of fragmentation, and changes in the ion mobilities of the analyte ions for analytes with suitable molecular structures and gas acidity.

An economical setup for atmospheric pressure chemical ionization drift tube ion-mobility mass spectrometry

Ion-mobility (IM) separations-performed in conjunction with mass spectrometry (MS)-increase selectivity of MS analyses. However, IM-MS instruments are costly, and many laboratories are only equipped with standard MS instruments without an IM separation stage. Therefore, it is appealing to upgrade the existing mass spectrometers with low-cost IM separation devices. Such devices can be constructed using widely available materials such as printed-circuit boards (PCBs). We demonstrate coupling of an economical PCB-based IM spectrometer (disclosed previously) with a commercial triple quadrupole (QQQ) mass spectrometer. The presented PCB-IM-QQQ-MS system incorporates an atmospheric pressure chemical ionization (APCI) source, drift tube comprising desolvation and drift regions, ion gates, and transfer line to the mass spectrometer. The ion gating is accomplished with the aid of two floated pulsers. The separated ions are divided into packets, which are sequentially introduced to the mass spectrometer. Volatile organic compounds (VOCs) are transferred with the aid of nitrogen gas flow from the sample chamber to the APCI source. The operation of the system has been demonstrated using standard compounds. The limits of detection for 2,4-lutidine, (-)-nicotine, and pyridine are 2.02 × 10^-7 M, 1.54 × 10^-9 mol, and 4.79 × 10^-10 mol, respectively. The system was also used to monitor VOCs emitted from the porcine skin after exposure to nicotine patches, and VOCs released from meat undergoing the spoilage process. We believe this simple APCI-PCB-IM-QQQ-MS platform can be reproduced by others to augment the capabilities of the existing MS instrumentation.

Suitability of Short- and Long-Term Storage of Volatile Organic Compounds Samples in Syringe-Based Containers: A Comparison Study

The employment of advanced analytical techniques and instrumentation enables the tracing of volatile organic compounds (VOCs) in vestigial concentrations (ppbv-pptv range) for several emerging applications, such as the research of disease biomarkers in exhaled air, the detection of metabolites in several biological processes, and the detection of pollutants for air quality control. In this scope, the storage of gaseous samples is crucial for preserving the integrity and stability of the collected set of analytes. This study aims to assess the suitability of three commercially available syringes as air containers (AC) that are commonly used for the collection, storage, isolation, and transportation of samples: glass syringes with glass plungers (AC1), and two plastic syringes, one with plastic plungers (AC2), and one with rubbered plungers (AC3). For this purpose, 99 air samples with different times of storage (from 10 min to 24 h) were analyzed using a Gas Chromatography-Ion Mobility Spectrometry device and the degradation of the samples was properly assessed by comparing the changes in the VOCs' emission profiles. The quality of the method was assured by via the measurement of the blank's spectra before each experimental run, as well as by the consecutive measurement of the three replicates for each sample. A statistical analysis of the changes in the VOCs' emission patterns was performed using principal component analysis (PCA). The results, with a total explained variance of 93.61%, indicate that AC3 is the most suitable option for the long-term storage of air samples. Thus, AC3 containers demonstrated a higher capacity to preserve the stability and integrity of the analytes compared to AC1 and AC2. The findings of the short-term effects analysis, up to 1 h, confirm the suitability of all analyzed syringe-based containers for sample-transferring purposes in onsite analysis.

Electrospray Ion Mobility Spectrometer Based on Flexible Printed-Circuit Board Electrodes with Improved Resolving Power

An easily built drift tube instrument with ring electrodes made of rolled-up flexible printed circuit boards is reported. Its resolving power was maximized by careful attention to the drift tube geometry and the response time of the detector amplifier and by employing a high separation field strength. The separation of singly charged aliphatic quaternary ammonium ions introduced by electrospray was performed, and the measured resolving power was between 86 and 97% of the theoretical limit for three different drift tube lengths investigated. For the longest drift length of 30 cm, a resolving power of up to 228 was obtained. Three benzalkonium chlorides were also separated with resolving powers of over 210. The tristate injection scheme can also be used, with only a small loss of the separation performance compared to the two-state injection.

Differentiation of the Organoleptic Volatile Organic Compound Profile of Three Edible Seaweeds

The inclusion of seaweeds in daily-consumption food is a worthy-of-attention challenge due to their high nutritional value and potential health benefits. In this way, their composition, organoleptic profile, and toxicity must be assessed. This work focuses on studying the volatile organic compounds (VOCs) emitted by three edible seaweeds, Grateloupia turuturu, Codium tomentosum, and Bifurcaria bifurcata, with the aim of deepening the knowledge regarding their organoleptic profiles. Nine samples of each seaweed were prepared in glass vials, and the emitted headspace was analyzed, for the first time, with a gas chromatography-ion mobility spectrometry device, a highly sensitive technology. By statistically processing the collected data through PCA, it was possible to accurately differentiate the characteristic patterns of the three seaweeds with a total explained variance of 98%. If the data were pre-processed through PLS Regression, the total explained variance increased to 99.36%. The identification of 13 VOCs was accomplished through a developed database of compounds. These outstanding values in addition to the identification of the main emissions of VOCs and the utilization of a never-before-used technology prove the capacity of GC-IMS to differentiate edible seaweeds based solely on their volatile emissions, increase the knowledge regarding their organoleptic profiles, and provide an important step forward in the inclusion of these highly nutritional ingredients in the human diet.

CaptiveSpray Differential Ion Mobility Spectrometry Device with Enhanced Ion Transmission and Improved Resolving Power

A performance enhanced CaptiveSpray differential ion mobility device was designed and constructed by incorporating a circular channel and a gas flow homogenizing channel (GFHC) between the CaptiveSpray ion source and planar differential ion mobility spectrometry (DMS). The GFHC was used to reduce gas flow heterogeneity prior to the entrance of the DMS device. The optimal flared entrance greatly reduces gas flow velocity at the inlet region owing to its relatively large gas inlet interface, which assists in reducing disparities between the minimum and maximum gas velocity along the x-axis. The circular electrode was machined with channels along the x- and y-axis for the passage of auxiliary gas and was applied with a potential to focus the incoming ions from the CaptiveSpray source into the DMS channel. Using reserpine as a reference standard, substantial signal enhancement was achieved with a concomitant reduction of the peak width in the ionogram.

Flavor components detection and discrimination of isomers in Huaguo tea using headspace-gas chromatography-ion mobility spectrometry and multivariate statistical analysis

Aroma components are one of the crucial factors in dynamic processes analysis, quality control, and origin traceability. Various categories of Huaguo Tea possessed different taste due to the generation of aroma. In this study, a comprehensive analysis of volatiles was conducted for five popular Huaguo Tea samples (Lemon Slices, Bitter Gourd Slices, Citri Reticulatae Pericarpium, Red Lycium Barbarum, and Black Lycium Barbarum) via gas chromatography-ion mobility spectrometry (GC-IMS) combining with multivariate statistical strategies. Comparison analysis was achieved with the properties of visually and intuitively by drawing of topography plots. A total of one hundred and eighty volatiles were distinguished. Aliphatic isomers were identified simultaneously by fingerprint spectra. Alcohols, aldehydes, esters, and ketones were the most abundant volatiles in Huaguo Tea samples. To characterize the Huaguo Tea precisely and establish an analysis model for their classification, multivariate statistical analysis was applied to distinguish different Huaguo Tea. Satisfied discrimination was obtained by principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA) based on the HS-GC-IMS results with the robustness parameter (R²Y) of 99.4%, and prediction ability parameter (Q²) of 98.6%, respectively. The results provide a theoretical basis for aroma discrimination, isomer identification, and categories analysis of Huaguo Tea.

Rapid determination of ampyra in urine samples using dispersive liquid-liquid microextraction coupled with ion mobility spectrometry

Ampyra (AMP, 4-Aminopyridine) is a potassium channel blocker that attracts growing research interest due to its adverse effects at high doses. The fast analysis of AMP is challenging because it typically requires complex analytical techniques. In this research, we developed and validated a novel method to assess the fast and quantitative analysis of AMP from real samples. This method combines the strength of ion mobility spectrometry (IMS) for rapid detection and the dispersive liquid-liquid microextraction as a fast and effective preconcentration method for the preconcentration/extraction of AMP. In this method, Ag nanoparticles were used as modifier agents. Moreover, the proposed mechanism for interaction of AMP with AgNPs was investigated based on the quantum theory of atoms in molecules (QTAIM) analysis. Also, the sensitivity of the proposed method was improved through the application of a delay on the carrier gas flow after sample injection. Under the optimum conditions, the developed method detected AMP in the linear range of 0.4-16 μmol L^-1 with a detection limit of 0.12 µmol L^-1. Finally, the developed method was successfully employed to quantify AMP in urine samples. Method validation was performed by comparing our results with those obtained by HPLC-UV/Vis, confirming the applicability of the proposed method for the AMP analysis in real samples. The proposed method will open up a new door toward developing simple, fast, and effective analytical methods.

Deconvolution of overlapping peaks in ion mobility spectrometry based on a multiobjective dynamic teaching-learning-based optimization

RATIONALE

Because of its powerful analytical ability, ion mobility spectrometry (IMS) plays an important role in the field of mass spectrometry. However, one of the main defects of IMS is its low structural resolution, which leads to the phenomenon of peak overlap in the analysis of compounds with similar mass charge ratio.

METHODS

A multiobjective dynamic teaching-learning-based optimization (MDTLBO) method was proposed to separate IMS overlapping peaks. This method prevents local optimization and identifies peak model coefficients efficiently. In addition, the position information of particles largely reflects the half-peak width of IMS, which makes single peaks difficult to appear and coefficient identification easier.

RESULTS

The performance comparison of MDTLBO with other deconvolution methods (genetic algorithm, improved particle swarm optimization algorithm, and dynamic inertia weight particle swarm optimization algorithm) shows that the maximum deconvolution error of MDTLBO is only 0.7%, which is much lower than that for the other three methods. In addition, robustness is a performance index that reflects the advantages and disadvantages of the algorithm.

CONCLUSION

MBTLBO is more robust than other algorithms for separating overlapping peaks. The algorithm can separate the heavily overlapped mobility peaks, produce better analysis results, and improve the resolution of IMS.

Air Pollution and Radiation Monitoring in Collective Protection Facilities

It has become increasingly important to monitor environment contamination by such chemicals as chemical warfare agents (CWAs) and industrial toxic chemicals (TICs), as well as radiation hazards around and inside collective protection facilities. This is especially important given the increased risk of terrorist or military attacks. The Military Institute of Chemistry and Radiometry (MICR) has constructed and developed the ALERT device for the effective monitoring of these threats. This device uses sensors that detect chemical and radiological contaminations in the air. The CWA detector is an ion mobility spectrometer, TICs are detected by electrochemical sensors, and radiation hazards are detected via Geiger-Muller tubes. The system was designed to protect the crew from contamination. When chemical or radioactive contamination is detected at the air inlet for the shelter, air filtration through a carbon filter is activated. At this time, the air test procedure at the filter outlet is started to test the condition of the filter on an ongoing basis. After detecting contamination at the filter outlet, the system turns off the air pumping and the service can start the procedure of replacing the damaged carbon filter. This paper presents the results of laboratory testing of the ALERT gas alarm detector, which showed high measurements for important parameters, including sensitivity, repeatability, accuracy, and speed.

Graphene Oxide Thin Films for Detection and Quantification of Industrially Relevant Alcohols and Acetic Acid

Industrial environments are frequently composed of potentially toxic and hazardous compounds. Volatile organic compounds (VOCs) are one of the most concerning categories of analytes commonly existent in the indoor air of factories' facilities. The sources of VOCs in the industrial context are abundant and a vast range of human health conditions and pathologies are known to be caused by both short- and long-term exposures. Hence, accurate and rapid detection, identification, and quantification of VOCs in industrial environments are mandatory issues. This work demonstrates that graphene oxide (GO) thin films can be used to distinguish acetic acid, ethanol, isopropanol, and methanol, major analytes for the field of industrial air quality, using the electronic nose concept based on impedance spectra measurements. The data were treated by principal component analysis. The sensor consists of polyethyleneimine (PEI) and GO layer-by-layer films deposited on ceramic supports coated with gold interdigitated electrodes. The electrical characterization of this sensor in the presence of the VOCs allows the identification of acetic acid in the concentration range from 24 to 120 ppm, and of ethanol, isopropanol, and methanol in a concentration range from 18 to 90 ppm, respectively. Moreover, the results allows the quantification of acetic acid, ethanol, and isopropanol concentrations with sensitivity values of (3.03±0.12)∗104, (-1.15±0.19)∗104, and (-1.1±0.50)∗104 mL^-1, respectively. The resolution of this sensor to detect the different analytes is lower than 0.04 ppm, which means it is an interesting sensor for use as an electronic nose for the detection of VOCs.

The Discrimination and Characterization of Volatile Organic Compounds in Different Areas of Zanthoxylum bungeanum Pericarps and Leaves by HS-GC-IMS and HS-SPME-GC-MS

The pericarps of Zanthoxylum bungeanum (ZBP) and leaves of Zanthoxylum bungeanum (ZBL) are popular spices in China, and they have pharmacological activities as well. In this experiment, the volatile organic compounds (VOCs) of the pericarps of Zanthoxylum bungeanum in Sichuan (SJ) and its leaves (SJY) and the pericarps of Zanthoxylum bungeanum in Shaanxi (SHJ) and its leaves (SHJY) were analyzed by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The fingerprint of HS-GC-IMS and the heat maps of HS-SPME-GC-MS were established. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were performed. The results showed that a total of 95 components were identified, 62 components identified by HS-SPME-GC-MS and 40 components identified by HS-GC-IMS, of which 7 were the same. The analysis found that SJ and SHJ were obviously distinguished, while SJY and SHJY were not. There were considerably fewer VOCs in the leaves than in the pericarps. In the characterization of the VOCs of ZBL and ZBP, the flavor of ZBP was more acrid and stronger, while the flavor of ZBL was lighter and slightly acrid. Thirteen and eleven differential markers were identified by HS-GC-IMS and HS-SPME-GC-MS, respectively. This is helpful in distinguishing between SHJ and SJ, which contributes to their quality evaluation.

Sampling Volatile Organic Compound Emissions from Consumer Products: A Review

Volatile organic compounds (VOCs) are common constituents of many consumer products. Although many VOCs are generally considered harmless at low concentrations, some compound classes represent substances of concern in relation to human (inhalation) exposure and can elicit adverse health effects, especially when concentrations build up, such as in indoor settings. Determining VOC emissions from consumer products, such as toys, utensils or decorative articles, is of utmost importance to enable the assessment of inhalation exposure under real-world scenarios with respect to consumer safety. Due to the diverse sizes and shapes of such products, as well as their differing uses, a one-size-fits-all approach for measuring VOC emissions is not possible, thus, sampling procedures must be chosen carefully to best suit the sample under investigation. This review outlines the different sampling approaches for characterizing VOC emissions from consumer products, including headspace and emission test chamber methods. The advantages and disadvantages of each sampling technique are discussed in relation to their time and cost efficiency, as well as their suitability to realistically assess VOC inhalation exposures.

Gas Chromatography - Ion Mobility Spectrometry as a tool for quick detection of hazardous volatile organic compounds in indoor and ambient air: A university campus case study

Society's concerns about the citizens' exposure to possibly dangerous environments have recently risen; nevertheless, the assessment of indoor air quality still represents a major contemporary challenge. The volatile organic compounds (VOCs) are among the main factors responsible for deteriorating air quality conditions. These analytes are very common in daily-use environments and they can be extremely hazardous to human health, even at trace concentrations levels. For these reasons, their quick detection, identification, and quantification are crucial tasks, especially for indoor and heavily-populated scenarios, where the exposure time is usually quite long. In this work, a Gas Chromatography - Ion Mobility Spectrometry (GC-IMS) device was used for continuous monitoring indoor and ambient air environments at a large-scale, due to its outstanding levels of sensibility, selectivity, analytical flexibility, and almost real-time monitoring capability. A total of 496 spectra were collected from 15 locations of a university campus and posteriorly analysed. Overall, 23 compounds were identified among the 31 detected. Some of them, like Ethanol and 2-Propanol, were reported as being very hazardous to the human organism, especially in indoor environments. The achieved results confirmed the suitability of GC-IMS technology for air quality assessment and monitoring of VOCs and, more importantly, proved how dangerous indoor environments can be in scenarios of continuous exposure.

Almost perfect sequence modulated multiplexing ion mobility spectrometry

RATIONALE

Multiplexing ion mobility spectrometry with multiple ion injection pulses was used to achieve a high duty cycle and thus improve the signal-to-noise (S/N) ratio while maintaining high resolving power compared with the traditional single-pulse signal averaging method. Historically, an ion mobility spectrum was reconstructed by various multiplexing methods including Fourier transform ion mobility spectrometry (FT-IMS), Hadamard transform ion mobility spectrometry (HT-IMS), and linear frequency modulation correlation ion mobility spectrometry (LFM-CIMS) sequence or Barker code.

METHODS

To achieve an artifact-free multiplexing ion mobility spectrum, an almost perfect sequence (APS) with correlation technique was proposed to modulate the Bradbury-Nielson ion gate and was compared with FT-IMS, HT-IMS, LFM-IMS, and the traditional single-pulse signal averaging method.

RESULTS

Experimental results showed that there are no artifact peaks in the APS-IMS spectra except an inverted mirror peak, and the S/N ratio was improved 5-8 times with a repetition time of 40-60 ms, corresponding to the improvement in the duty cycle. With the same duty cycle and similar acquisition time, APS-IMS showed a higher S/N ratio than HT-IMS for its unique autocorrelation response.

CONCLUSIONS

The APS-IMS technique offered a higher duty cycle and relatively shorter modulation period compared with reported multiplexing methods and is suitable to track rapidly changing signals without losing information and adding extra transformation artifact peaks.

A Strategy for Identification and Structural Characterization of Compounds from Plantago asiatica L. by Liquid Chromatography-Mass Spectrometry Combined with Ion Mobility Spectrometry

Plantago asiatica L. (PAL) as a medicinal and edible plant is rich in chemical compounds, which makes the systematic and comprehensive characterization of its components challenging. In this study, an integrated strategy based on three-dimensional separation including AB-8 macroporous resin column chromatography, ultra-high performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF MS), and ultra-high performance liquid chromatography-mass spectrometry with ion-mobility spectrometry (UHPLC-IM-MS) was established and used to separate and identify the structures of compounds from PAL. The extracts of PAL were firstly separated into three parts by AB-8 macroporous resin and further separated and identified by UHPLC-Q-TOF MS and UHPLC-IM-MS, respectively. Additionally, UHPLC-IM-MS was used to identify isomers and coeluting compounds, so that the product ions appearing at the same retention time (RT)can clearly distinguish where the parent ion belongs by their different drift times. UNIFI software was used for data processing and structure identification. A total of 86 compounds, including triterpenes, iridoids, phenylethanoid glycosides, guanidine derivatives, organic acids, and fatty acids, were identified by using MS information and fragment ion information provided by UHPLC-Q-TOF MS and UHPLC-IM-MS. In particular, a pair of isoforms of plantagoside from PAL were detected and identified by UHPLC-IM-MS combined with the theoretical calculation method for the first time. In conclusion, the AB-8 macroporous resin column chromatography can separate the main compounds of PAL and enrich the trace compounds. Combining UHPLC-IM-MS and UHPLC-Q-TOF MS can obtain not only more fragments but also their unique drift times and RT, which is more conducive to the identification of complex systems, especially isomers. This proposed strategy can provide an effective method to separate and identify chemical components, and distinguish isomers in the complex system of traditional Chinese medicine (TCM).

Investigation of different alcoholic modifiers for the separation and determination of two isomers of dinitrotoluene (2,4 and 2,6) by ion mobility spectrometry

Some alcoholic modifier gases were applied to separate isomer peaks in ion mobility spectrometry (IMS). Different mechanisms have been investigated on the separation, such as collision cross-section and analyte-modifier cluster formation. In this regard, some parameters that affected the cluster formation, such as dipole moment, electron affinity, the position of functional groups, and the modifier structure, were evaluated. On the other hand, some effective experimental parameters, including cell temperature and the flow rates of the drift and modifier gases, were also optimized. The combination of dispersive liquid-liquid microextraction with thin-film evaporation (DLLME-TFE) was used as a sample preparation method for the extraction of 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT) isomers (as the target analytes). Isobutanol was selected as the alcoholic modifier to separate the ion molecular peaks of these isomers. The limit of detection and the limit of quantification obtained were 15 and 50 μg L^-1 , and the linear dynamic range (50-700 μg L^-1 ) with coefficient of determination of 0.9941 and 0.9914 were obtained for 2,4-DNT and 2,6-DNT, respectively. The intra- and inter-day relative standard deviations were obtained between 3% and 5%. For validation of the method, determination of the isomers was accomplished for a red wastewater field sample, resulting in relative recovery values of about 96%.

Diversity of Volatile Compounds in Raw Milk with Different n-6 to n-3 Fatty Acid Ratio

Simple Summary

In production, milk that is more beneficial to human health is obtained by adjusting the ratio of n-6 and n-3 fatty acids; however, the effect the regulation will have on the volatile substances in milk is unknown. In this study, gas chromatography–ion mobility spectrometry combined with principal component analysis was used to establish the fingerprint of volatile substances in raw milk to identify the types of volatile substances. The results show that a total of 34 target compounds were identified, and there were differences in the types and contents of volatile compounds among different treatment groups. The main reason for these differences is that lipid is degraded and aldehydes and ketones are produced in the adjusted-proportion group.

Abstract

Fatty acid profiles may affect the flavor of milk. The diversity of volatile compounds in raw milk with different ratios of n-6 to n-3 fatty acids (8:1, 4:1, and 3:1) was studied. Gas chromatography–ion mobility spectroscopy (GC–IMS) is a promising technology for the accurate characterization and detection of volatile organic compounds in agricultural products, but its application in milk is rare or even unavailable. In this experiment, GC–IMS fingerprints along with principal component analysis (PCA) were used to study the flavor fingerprints of fresh milk samples with different percentages. Thirty-four typical target compounds were identified in total. A diversity of flavor compounds in raw milk with different n-6/n-3 was observed. After reduction of the proportion, the concentrations of volatile compounds, such as hexanoic acid (dimer and monomer), ethyl acetate, and 2-methylpropanoic acid (dimer and monomer) decreased, while those of 4-methyl-2-pentanone, pentanal, and acetone increased. We carried out PCA according to the signal strength of the identified volatile compounds, and the examination showed that it could precisely make a distinction among the samples in a comparative space. In conclusion, the results show that the volatile compounds are different as the proportion is different. The volatile compounds in raw milk are mainly hexanoic acid, ethyl acetate, and 2-methylpropanoic acid. After adjustment of the ratio, the flavor substances of the medium-ratio (MR) group were mainly ketones, while those of the low-ratio (LR) group were aldehydes. Therefore, in production, reducing the impact on volatile substances while adjusting the proportion of n-6 and n-3 fatty acids to obtain functional dairy products should be taken into consideration.

Metabolic Footprint Analysis of Volatile Organic Compounds by Gas Chromatography-Ion Mobility Spectrometry to Discriminate Mandarin Fish (Siniperca chuatsi) at Different Fermentation Stages

Chinese fermented mandarin fish (Siniperca chuatsi) have unique aroma characteristics that are appreciated by local consumers. In this study, electronic nose (E-nose) and gas chromatography–ion mobility spectrometry analyses were combined to establish a volatile fingerprint of fermented mandarin fish during fermentation. Clear separation of the data allowed mandarin fish samples at different fermentation stages to be distinguishing using E-nose analysis. Forty-three volatile organic compounds were identified during fermentation. Additionally, partial least squares discrimination analysis was performed to screen for different VOC metabolites in the fermented mandarin fish; the levels of six VOCs changed significantly during fermentation (variable importance in projection >1; p < 0.05). Three VOCs, i.e., hexanal-D, nonanal, and limonene were identified as potential biomarkers for fermentation. This study provided a theoretical basis for flavor real-time monitoring and quality control of traditional mandarin fish fermentation.

Coulombic effects on resolution of ion mobility spectrometry and its application in online qualitative analysis

Ion mobility spectrometry is an important gas analysis method used in the rapid detection field. However, due to a lacking of explicit mathematical model of ion peak, it is difficult to extract characteristic analyte peaks from a spectrum containing overlapping peaks to achieve online qualitative analysis. Here, we present an asymmetric peak model for processing ion mobility peaks. For the asymmetric peak model, the key is to accurately estimate the standard deviation of the peak model and the fitting function of the tailing edge. We focused on the Coulombic effects on resolution of ion mobility spectrometry based on a new hypothesis of ion cloud shape and derived a formula for calculating the standard deviation taking the initial pulse width, diffusion and Coulomb repulsion factors into account. The proposed asymmetric peak model combines the advantages of optimal physical and chemical interpretation and explicit mathematical meaning. A fast decomposition method based on the peak model was developed to decompose overlapping peaks. Two overlapping simulated data sets and one real data set (a mixture of acetone and methyl salicylate) were used to test the method. The results indicated that our proposed method successfully decomposed the overlapping spectrum into individual peaks and performed markedly better than other three available methods in terms of the execution time. The proposed method meets the requirements for online qualitative analysis.

Limitations of GC-QTOF-MS Technique in Identification of Odorous Compounds from Wastewater: The Application of GC-IMS as Supplement for Odor Profiling

Odorous emissions from wastewater treatment plants (WWTPs) cause negative impacts on the surrounding areas and possible health risks on nearby residents. However, the efficient and reliable identification of WWTPs’ odorants is still challenging. In this study, odorous volatile organic compounds (VOCs) from domestic wastewater at different processing units were profiled and identified using gas chromatography-ion mobility spectrometry (GC-IMS) and gas chromatography quadrupole-time-of-flight mass spectrometry (GC-QTOF-MS). The GC-QTOF-MS results confirmed the odor contribution of sulfur organic compounds in wastewater before primary sedimentation and ruled out the significance of most of the hydrocarbons in wastewater odor. The problems in odorous compounds analysis using GC-QTOF-MS were discussed. GC-IMS was developed for visualized analysis on composition characteristics of odorants. Varied volatile compounds were detected by GC-IMS, mainly oxygen-containing VOCs including alcohols, fatty acids, aldehydes and ketones with low odor threshold values. The fingerprint plot of IMS spectra showed the variation in VOCs’ composition, indicating the changes of wastewater quality during treatment process. The GC-IMS technique may provide an efficient profiling method for the changes of inlet water and performance of treatment process at WWTPs.

Characterization of the volatile organic compounds produced from avocado during ripening by gas chromatography ion mobility spectrometry

BACKGROUND

The volatile organic compounds (VOCs) produced from avocados during storage may be distinct at different periods, and this difference may be related to their degree of maturity, for which no relevant research has been conducted yet.

RESULTS

A total of 30 typical target compounds were identified by gas chromatography-ion mobility spectrometry (GC-IMS) combined with principal component analysis (PCA) for the VOCs produced during the post-harvesting process of avocado. With an increase in storage time, the VOCs content produced by avocado due to ripening continued to increase, and the uptrend was particularly obvious on day 13. The storage time of avocado could be distinguished according to the PC1 and PC2 values in the PCA chart.

CONCLUSION

GC-IMS detection combined with PCA was used to establish the fingerprints of VOCs in avocado for the first time. The maturity of avocados was determined by identifying the signal strength of characteristic VOCs, and this method could be of great potential to predict the maturity of fruits in the future. © 2020 Society of Chemical Industry.

A Comparison of Various Algorithms for Classification of Food Scents Measured with an Ion Mobility Spectrometry

The present aim was to compare the accuracy of several algorithms in classifying data collected from food scent samples. Measurements using an electronic nose (eNose) can be used for classification of different scents. An eNose was used to measure scent samples from seven food scent sources, both from an open plate and a sealed jar. The k-Nearest Neighbour (k-NN) classifier provides reasonable accuracy under certain conditions and uses traditionally the Euclidean distance for measuring the similarity of samples. Therefore, it was used as a baseline distance metric for the k-NN in this paper. Its classification accuracy was compared with the accuracies of the k-NN with 66 alternative distance metrics. In addition, 18 other classifiers were tested with raw eNose data. For each classifier various parameter settings were tried and compared. Overall, 304 different classifier variations were tested, which differed from each other in at least one parameter value. The results showed that Quadratic Discriminant Analysis, MLPClassifier, C-Support Vector Classification (SVC), and several different single hidden layer Neural Networks yielded lower misclassification rates applied to the raw data than k-NN with Euclidean distance. Both MLP Classifiers and SVC yielded misclassification rates of less than 3% when applied to raw data. Furthermore, when applied both to the raw data and the data preprocessed by principal component analysis that explained at least 95% or 99% of the total variance in the raw data, Quadratic Discriminant Analysis outperformed the other classifiers. The findings of this study can be used for further algorithm development. They can also be used, for example, to improve the estimation of storage times of fruit.

An emerging powerful technique for distinguishing isomers: Trapped ion mobility spectrometry time-of-flight mass spectrometry for rapid characterization of estrogen isomers

RATIONALE

Isomer metabolites are involved in metabolic pathways, and their characterization is essential but remains challenging even using high-performance analytical platforms. The addition of ion mobility prior to mass analysis can help to separate isomers. Here, the ability of a recently developed trapped ion mobility spectrometry system to separate metabolite isomers was examined.

METHODS

Three pairs of estrogen isomers were studied as a model of isomeric metabolites under both negative and positive electrospray ionization (ESI) modes using a commercial trapped ion mobility spectrometry-TOF mass spectrometer. The standard metabolites were also spiked into human urine to evaluate the efficiency of trapped ion mobility spectrometry to separate isomers in complex mixtures.

RESULTS

The estradiol glucuronide isomers (E₂ β-3G and E₂ β-17G) could be distinguished as deprotonated species, while the estradiol epimers (E₂ β and E₂ α) and the methoxyestradiol isomers (2-MeO-E₂ β and 4-MeO-E₂ β) were separated as lithiated adducts in positive ionization mode. When performing analyses in the urine matrix, no alteration in the ion mobility resolving power was observed and the measured collision cross section (CCS) values varied by less than 1.0%.

CONCLUSIONS

The trapped ion mobility spectrometry-TOF mass spectrometer enabled the separation of the metabolite isomers with very small differences in CCS values (ΔCCS% = 2%). It is shown to be an effective tool for the rapid characterization of isomers in complex matrices.

Molecularly imprinted polymer-based device for field collection of oral fluid samples for cocaine identification

In this paper, a low-cost, rapid, easy, and potentially portable tool for the identification of cocaine and its semi-quantitative determination in oral fluid has been proposed. A field collection device has been designed, based on a cotton pad with an indicator and a molecularly imprinted polymer (MIP) sorbent, to selective retain cocaine from oral fluid components. After sample collection, cocaine is transferred by using phosphate buffer to the MIP and then eluted with 2-propanol. The obtained extract is analysed by ion mobility spectrometry (IMS), providing a cut-off value of 20 µg L^-1 that identifies 100 % true-positive and 95 % true-negative samples. The MIP-IMS procedure has been validated by the analysis of oral fluid samples, collected from cocaine users at recreation environments, by comparing the results with lateral flow immunoassay and chromatographic reference methods. Thus, the proposed methodology allows a simple and fast cocaine identification that can be carried out in field by non-specialized personnel, such as health personnel, law enforcement bodies, and customs staff.

Identification of new, very long-chain polyunsaturated fatty acids in fish by gas chromatography coupled to quadrupole/time-of-flight mass spectrometry with atmospheric pressure chemical ionization

The characterization of very long-chain (>C24) polyunsaturated fatty acids (VLC-PUFAs), which are essential in the vision, neural function, and reproduction of vertebrates, is challenging because of the lack of reference standards and their very low concentrations in certain lipid classes. In this research, we have developed a new methodology for VLC-PUFA identification based on gas chromatography coupled to quadrupole/time-of-flight mass spectrometry with an atmospheric pressure chemical ionization source (GC-APCI-QTOF MS). The mass accuracy attainable with the innovative QTOF instrument, together with the soft ionization of the APCI source, provides valuable information on the intact molecule, traditionally lost with electron ionization sources due to the extensive fragmentation suffered. We have identified, for the first time, VLC-PUFAs with chains up to 44 carbons in eyes, brain, and gonads of gilthead sea bream, a commercially important fish in the Mediterranean. The added value of ion mobility-mass spectrometry (IMS), recently developed in combination with GC-QTOF MS, and the contribution of the collisional cross section (CCS) parameter in the characterization of novel VLC-PUFAs (for which reference standards are not available) have been also evaluated. The methodology developed has allowed assessing qualitative differences between farmed and wild fish, and opens new perspectives in a still scarcely known field of research.

On-Line Coupling of Chip-Electrochromatography and Ion Mobility Spectrometry

We report the first hyphenation of chip-electrochromatography (ChEC) with ion mobility spectrometry (IMS). This approach combines the separation power of two electrokinetically driven separation techniques, the first in liquid phase and the second in gas phase, with a label-free detection of the analytes. For achieving this, a microfluidic glass chip incorporating a monolithic separation column, a nanofluidic liquid junction for providing post-column electrical contact, and a monolithically integrated electrospray emitter was developed. This device was successfully coupled to a custom-built high-resolution drift tube IMS with shifted potentials. After proof-of-concept studies in which a mixture of five model compounds was analyzed in less than 80 s, this first ChEC-IMS system was applied to a more complex sample, the analysis of herbicides spiked in the wine matrix. The use of ChEC before IMS detection not only facilitated the peak allocation and increased the peak capacity but also enabled analyte quantification. As both, ChEC and IMS work at ambient conditions and are driven by high voltages, no bulky pumping systems are needed, neither for the hydrodynamic pumping of the mobile phase as in high-performance liquid chromatography nor for generating a vacuum system as in mass spectrometry. Accordingly, the approach has great potential as a portable analytical system for field analysis of complex mixtures.

Gas chromatographic-ion mobility spectrometry combined with a multivariate analysis model exploring the characteristic changes of odor components during the processing of black sesame

Black sesame (Sesamum indicum L.) is a Chinese dietary herb that has been widely used in the medical and healthcare fields in China. According to the theory of Traditional Chinese medicine processing, reasonable processing (steaming and drying many times) can increase the tonic effect and reduce the adverse factors generated during long-term use. At present, the processing degree of black sesame is mainly judged based on subjective experience. However, due to the lack of objective and quantitative control indicators, quality fluctuations easily occur. Therefore, for better application, its processing technology needs scientific monitoring methods. Herein a gas chromatography-ion mobility spectrometry (GC-IMS) technique was applied as a monitoring method to differentiate the processed products of black sesame in different processing stages. The response data of volatile components obtained from the samples were processed by the built-in data processing software in the instrument to identify the different components for further principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA). From fingerprint comparison, 70 differential signal peaks were screened, 32 of which were qualitatively identified, mainly monomers and dimers of 20 compounds. On this basis, the PCA model shows that there was a significant difference between the raw product (S1) and the processed products (H1-9); moreover, there was a certain correlation between the differential changes of samples in different processing stages (H1-9) and the processing times. The OPLS-DA model specifically shows the differential components in the processing with potential characteristics peaks of 41, 105, n-nonanal, 2 and ethanol can discriminate whether the BS has undergone the first processed. And the dynamic changes of the three characteristic peaks of 1-hexanol, acetic acid and 107 can determine the specific degree of processing of BS. The research proves that GC-IMS combined with a multivariate analysis model can provide scientific data for identifying the characteristic odor components of black sesame.

Changes in the volatile components of squid (illex argentinus) for different cooking methods via headspace-gas chromatography-ion mobility spectrometry

Squid products are becoming more and more popular with consumers because of their high yields and nutrition, including novel textures with desirable sensory properties. However, it has not been determined whether the cooking method has effects on the flavor of the squid. In this study, the aroma and volatile substances of squid samples from different cooking methods (boiled, steamed, sous vide) were determined and analyzed by headspace-gas chromatography-ion mobility spectrometry and differentiated by using, as well, an electronic nose and sensory evaluation. A total of 43 characteristic flavor compounds were identified. Based on the signal intensity of the identified violate compounds, we established a fingerprint of heat-treated squid from different cooking methods. Due to the long-term low-temperature heating conditions under vacuum, the flavor of sous vide squid is different from steamed and boiled squid, and it has unique special flavor compounds. Different cooking methods can affect the aroma of squid, providing support for the industrial production of squid.

Variations of volatile flavour compounds in finger citron (Citrus medica L. var. sarcodactylis) pickling process revealed by E-nose, HS-SPME-GC-MS and HS-GC-IMS

The pickled products of finger citron are famous in southern China for their unique taste and flavor. Although pickling process involves complex treatments including salting, desalting, sugaring, cooking and drying, extended shelf-life up to ten years after pickling can be achieved. In this study, the variations of volatile flavour components in the pickling process of finger citron were investigated by electronic nose (E-nose), headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). HS-SPME-GC-MS identified 85 substances, and HS-GC-IMS identified 81 substances, including terpenoids (21), aromatic hydrocarbons (11), alcohols (11), aldehydes (10), esters (7), phenols (6), acids (5), ethers (2), ketones (2), and other species (10). Linalool, limonene, (E)-3,7-dimethyl-1,3,6-octatriene, myrcene, 3-carene, β-pinene, α-pinene, terpinolene, 1-methyl-4-(1-methylethyl)-1,4-cyclohexadiene, α-terpinene, (S)-β-bisabolene, 1-isopropyl-2-methylbenzene and 1-methyl-4-(1-methylethenyl)-benzene were the stable substances at relatively high contents in finger citron at different pickling process. Salting and drying steps in the pickling process exerted greatest influence on the volatile components of finger citron. Salting promoted the generation of aldehydes, esters and acids, but led to the disappearance of alcohols, while drying promoted the generation of alcohols, phenols, aldehydes and acids at the expense of reduction in terpenoids. Our study revealed that the characteristic volatile compounds of finger citron pickled products was mainly formed by the biological reactions in the salting stage and thermal chemical transformations in the drying stage. This study also validated the suitability of E-nose combined with HS-SPME-GC-MS and HS-GC-IMS in tracking the changes of volatile components in finger citron during the pickling process.

Development of homogeneous liquid-liquid extraction combined with dispersive liquid-liquid microextraction based on solidification of floating droplets of a ternary component deep eutectic solvent for the analysis of antibiotic residues in sausage samples prior to ion mobility spectrometry

In this study, a combination of homogeneous liquid-liquid extraction and dispersive liquid-liquid microextraction based on solidification of a deep eutectic solvent has been utilized as an efficient method for the extraction of three widely used antibiotics (oxytetracycline, penicillin G, and tilmicosin) from sausage samples. In this method, initially the antibiotics are extracted from the powdered sausage sample into acetonitrile and then, to concentrate the analytes and achieve a high sensitivity, the obtained acetonitrile is mixed with an extraction solvent (a newly synthesized water-immiscible deep eutectic solvent with a melting point near room temperature), and the obtained mixture is rapidly injected into deionized water. In the next step, the mixture is transferred into an ice bath and the solidified extraction solvent containing the analytes is removed and dissolved in ACN. For quantitative analysis, this phase is taken and injected into an ion mobility spectrometer which operated in the positive mode and is equipped with a continuous corona discharge ionizer. This instrumental technique characterizes molecules based on the gaseous phase mobility of their ions formed at ambient pressure and under an electric field. Under the optimum conditions, limits of detection and quantification were achieved in the ranges of 1.52-2.73 and 5.1-9.1 ng g^-1, respectively. The relative standard deviations were less than 8% for intra- (n = 6) and inter-day (n = 4) precisions at a concentration of 20 ng g^-1 of each analyte. Finally, the proposed method was applied to the analysis of the studied antibiotics in fifteen different sausage samples marketed in Tabriz, Iran. Oxytetracycline was determined in three of the studied sausage samples.

Noncovalent Complexes of Cyclodextrin with Small Organic Molecules: Applications and Insights into Host-Guest Interactions in the Gas Phase and Condensed Phase

Cyclodextrins (CDs) have drawn a lot of attention from the scientific communities as a model system for host–guest chemistry and also due to its variety of applications in the pharmaceutical, cosmetic, food, textile, separation science, and essential oil industries. The formation of the inclusion complexes enables these applications in the condensed phases, which have been confirmed by nuclear magnetic resonance (NMR) spectroscopy, X-ray crystallography, and other methodologies. The advent of soft ionization techniques that can transfer the solution-phase noncovalent complexes to the gas phase has allowed for extensive examination of these complexes and provides valuable insight into the principles governing the formation of gaseous noncovalent complexes. As for the CDs’ host–guest chemistry in the gas phase, there has been a controversial issue as to whether noncovalent complexes are inclusion conformers reflecting the solution-phase structure of the complex or not. In this review, the basic principles governing CD’s host–guest complex formation will be described. Applications and structures of CDs in the condensed phases will also be presented. More importantly, the experimental and theoretical evidence supporting the two opposing views for the CD–guest structures in the gas phase will be intensively reviewed. These include data obtained via mass spectrometry, ion mobility measurements, infrared multiphoton dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations.