Solid Phase Mesh Enhanced Sorption from Headspace (SPMESH) Coupled to DART-MS for Rapid Quantification of Trace-Level Volatiles

Selective Sampling to and Desorption from Single Solid-Phase Microextraction Arrow Fiber for Replicative and Quantitative Analysis

New analytical functionality is demonstrated with an enclosed interface that joins a solid phase microextraction (SPME) device, a direct analysis in real time (DART) probe, and a high-resolution mass spectrometer. With a single 20 mm long SPME Arrow, the interface is able to perform five discrete DART analyses on different areas of the same fiber in 1 min of practical operation time. Three-fiber replicates for 15 runs total produce 15% or better center of variance (CV) values for both volatile headspace sampling and direct immersion sampling of a solvated analyte. Chemometric analysis of rapidly acquired headspace data is able to distinguish volatile profiles. Selective desorption within the interface also confers the ability to selectively sample to discrete areas of a fiber, and three different headspace samples or five different liquid samples can be acquired and differentiated with one Arrow. A five-point standard addition curve is constructed to measure the concentration of the solvated analyte. Unmodified commercial components of the analysis system include the fiber itself, the Orbitrap and AccuTOF mass spectrometer platforms, and the conditioning gas chromatograph inlet. Machine diagrams for the SPME-DART interface and Arrow fiber holder are included.

Rapid headspace solid-phase microextraction sheets with direct analysis in real time mass spectrometry (SPMESH-DART-MS) of derivatized volatile phenols in grape juices and wines

Volatile phenols possess "smoky, spicy" aromas and are routinely measured in grapes, wines and other foodstuffs for quality control. Routine analyses of volatile phenols rely on gas chromatography - mass spectrometry (GC-MS), but slow throughput of GC-MS can cause challenges during times of surge demand, i.e. following 'smoke taint' events involving forest fires near vineyards. Parallel extraction of headspace volatiles onto sorbent sheets (HS-SPMESH) followed by direct analysis in real time mass spectrometry (DART-MS) is a rapid alternative to conventional GC-MS approaches. However, HS-SPMESH extraction is poorly suited for lower volatility odorants, including volatile phenols. This work reports development and validation of an HS-SPMESH-DART-MS approach for five volatile phenols (4-ethylphenol, 4-ethylguiacol, guaiacol, 4-methylguaiacol, and cresols). Prior to HS-SPMESH extraction, volatile phenols were acetylated to facilitate their extraction. A unique feature of this work was the use of d₆-Ac₂O as a derivatizing agent to overcome issues with isobaric interferences inherent to chromatography-free MS techniques. The use of alkaline conditions during derivatization resulted in cumulative measurement of both free and bound forms of volatile phenols. The validated HS-SPMESH-DART-MS method achieved a throughput of 24 samples in ∼60 min (including derivatization and extraction time) with low limits of detection (<1 μg L^-1) and good repeatability (3-6% RSD) in grape and wine matrices. Validation experiments with smoke-tainted grape samples indicated good correlation between total (free + bound) volatile phenols measured by HS-SPMESH-DART-MS and a gold standard GC-MS method.

Rapid Screening and Quantification of PFAS Enabled by SPME-DART-MS

Per- and polyfluoroalkyl substances (PFAS), an emerging class of toxic anthropogenic chemicals persistent in the environment, are currently regulated at the low part-per-trillion level worldwide in drinking water. Quantification and screening of these compounds currently rely primarily on liquid chromatography hyphenated to mass spectrometry (LC-MS). The growing need for quicker and more robust analysis in routine monitoring has been, in many ways, spearheaded by the advent of direct ambient mass spectrometry (AMS) technologies. Direct analysis in real time (DART), a plasma-based ambient ionization technique that permits rapid automated analysis, effectively ionizes a broad range of compounds, including PFAS. This work evaluates the performance of DART-MS for the screening and quantification of PFAS of different chemical classes, employing a central composite design (CCD) to better understand the interactions of DART parameters on their ionization. Furthermore, in-source fragmentation of the model PFAS was investigated based on the DART parameters evaluated. Preconcentration of PFAS from water samples was achieved by solid phase microextraction (SPME), and extracts were analyzed using the optimized DART-MS conditions, which allowed obtaining linear dynamic ranges (LDRs) within 10 and 5000 ng/L and LOQs of 10, 25, and 50 ng/L for all analytes. Instrumental analysis was achieved in less than 20 s per sample.

Effect of 2,5-Dicarbonyl-3-Isobutyl-Piperazine on 3-Isobutyl-2-Methoxypyrazine Biosynthesis in Wine Grape

The metabolic pathway of 3-alkyl-2-methoxypyrazines (MPs) in grape remains largely unclear except for the final step. In this study, the 2,5-dicarbonyl-3-isobutyl-piperazine (DCIP), which is proposed as the key intermediate of 3-isobutyl-2-methoxypyrazine (IBMP) biosynthesis, was incorporated into Cabernet Sauvignon clusters in situ using a soaking method. The IBMP concentration of grape and the expression patterns of VvOMTs in berry skin were monitored over two consecutive years. The results showed that the IBMP concentration of grape treated with DCIP was significantly increased at maturity in both years. The relative expression levels of VvOMT1 and VvOMT3 in berry skin were positively correlated with the IBMP accumulation. After DCIP incorporation, the relative expression level of VvOMT1 and particularly that of VvOMT3 were obviously up-regulated and closely mirrored the IBMP accumulation pattern in two consecutive years. Therefore, we speculate that DCIP may be a key intermediate involved in the biosynthesis of IBMP and plays an important role in regulating IBMP accumulation.

Direct Coupling of SPME to Mass Spectrometry

Solid-phase microextraction devices are normally analyzed by gas or liquid chromatography. Their use has become increasingly widespread since their introduction in 1990, and nowadays most analytical laboratories use or have used SPME as an efficient and green method to perform analyte extraction and sample clean-up in one step. The SPME technique is intrinsically flexible, and allows for a high degree of optimization with regard to the extracting phase, as well as the way sample is analyzed. Since its introduction, researchers have been trying different ways to transfer analytes extracted from the solid phase to a mass spectrometer, with the aim to increase throughput and reduce solvent, gas usage and costs associated with conventional chromatographic techniques. Furthermore, but not less important, for pure fun of developing new, more efficient and sensitive analytical strategies! This chapter aims at providing a comprehensive overview of the most relevant non-chromatographic mass spectrometric approaches developed for SPME. Technical aspects of each SPME-MS approach will be discussed, highlighting their advantages, disadvantages and future potential developments. Particular emphasis will be given on the most recent direct coupling approaches using novel ionization approaches, and a concise overview of the existing applications will also be provided.

Online coupling of matrix solid-phase dispersion to direct analysis in real time mass spectrometry for high-throughput analysis of regulated chemicals in consumer products

The current work is the first study on online coupling of matrix solid-phase dispersion (MSPD) to direct analysis in real time mass spectrometry (DART-MS) bridging with solid-phase analytical derivatization (SPAD) based on a graphene oxide nanosheets (GONs)-coated cotton swab. Proof-of-concept demonstrations were explored for high-throughput analysis of a diversity of regulated chemicals in consumer products such as textiles, toys, and cosmetics. On-demand sorbent combinations were blended with samples, packed into MSPD columns, and mounted on a homemade 3D-printed rack module for automated sample feeding. To achieve good synergy between MSPD and DART-MS, a cotton swab with a conical tip deposited with GONs was attached to the bottom of the MSPD column. The swabs serve as a solid-phase microextraction probe for convenient enrichment of the eluted analytes from MSPD, thermal desorption of the enriched analytes by DART, and sensitive detection by a hybrid quadrupole-Orbitrap mass spectrometer. Furthermore, the utility of an on-swab SPAD strategy was demonstrated for the detection of formaldehyde by use of the derivatizing reagent of dansyl hydrazine, contributing to improved ionization efficiency without compromising the overall coherence of the analytical workflow. The MSPD-DART-MS methodology was systematically optimized and validated, obtaining acceptable recovery (71.7-110.3%), repeatability (11.8-19.3%), and sensitivity (limits of detection and quantitation in the ranges of 6.2-19.5 and 23.7-75.9 μg/kg) for 32 target analytes. The developed protocol streamlined sample extraction, clean-up, desorption, ionization, and detection, highlighting the appealing potential for high-throughput analysis of samples with complex matrices.

Optimized Solid-Phase Mesh-Enhanced Sorption from Headspace (SPMESH) for Rapid Sub-ng/kg Measurements of 3-Isobutyl-2-methoxypyrazine (IBMP) in Grapes

Parallel extraction of headspace volatiles from multiwell plates using sorbent sheets (HS-SPMESH) followed by direct analysis in real-time high-resolution mass spectrometry (DART-HRMS) can be used as a rapid alternative to solid-phase micro-extraction (SPME) gas-chromatography mass-spectrometry (GC-MS) for trace level volatile analyses. However, an earlier validation study of SPMESH-DART-MS using 3-isobutyl-2-methoxypyrazine (IBMP) in grape juice showed poor correlation between SPMESH-DART-MS and a gold standard SPME-GC-MS around the compound’s odor detection threshold (<10 ng/kg) in grape juice, and lacked sufficient sensitivity to detect IBMP at this concentration in grape homogenate. In this work, we report on the development and validation of an improved SPMESH extraction approach that lowers the limit of detection (LOD < 0.5 ng/kg), and regulates crosstalk between wells (<0.5%) over a calibration range of 0.5−100 ng/kg. The optimized SPMESH-DART-MS method was validated using Cabernet Sauvignon and Merlot grape samples harvested from commercial vineyards in the central valley of California (n = 302) and achieved good correlation and agreement with SPME-GC-MS (R2 = 0.84) over the native range of IBMP (<0.5−20 ng/kg). Coupling of SPMESH to a lower resolution triple quadrupole (QqQ)-MS via a new JumpShot-HTS DART source also achieved low ng/kg detection limits, and throughput was improved through positioning stage optimizations which reduced time spent on intra-well SPMESH areas.

Recent advances in proteomics and metabolomics in plants

Over the past decade, systems biology and plant-omics have increasingly become the main stream in plant biology research. New developments in mass spectrometry and bioinformatics tools, and methodological schema to integrate multi-omics data have leveraged recent advances in proteomics and metabolomics. These progresses are driving a rapid evolution in the field of plant research, greatly facilitating our understanding of the mechanistic aspects of plant metabolisms and the interactions of plants with their external environment. Here, we review the recent progresses in MS-based proteomics and metabolomics tools and workflows with a special focus on their applications to plant biology research using several case studies related to mechanistic understanding of stress response, gene/protein function characterization, metabolic and signaling pathways exploration, and natural product discovery. We also present a projection concerning future perspectives in MS-based proteomics and metabolomics development including their applications to and challenges for system biology. This review is intended to provide readers with an overview of how advanced MS technology, and integrated application of proteomics and metabolomics can be used to advance plant system biology research.

Utilization of Machine Learning for the Differentiation of Positional NPS Isomers with Direct Analysis in Real Time Mass Spectrometry

The differentiation of positional isomers is a well established analytical challenge for forensic laboratories. As more novel psychoactive substances (NPSs) are introduced to the illicit drug market, robust yet efficient methods of isomer identification are needed. Although current literature suggests that Direct Analysis in Real Time–Time-of-Flight mass spectrometry (DART-ToF) with in-source collision induced dissociation (is-CID) can be used to differentiate positional isomers, it is currently unclear whether this capability extends to positional isomers whose only structural difference is the precise location of a single substitution on an aromatic ring. The aim of this work was to determine whether chemometric analysis of DART-ToF data could offer forensic laboratories an alternative rapid and robust method of differentiating NPS positional ring isomers. To test the feasibility of this technique, three positional isomer sets (fluoroamphetamine, fluoromethamphetamine, and methylmethcathinone) were analyzed. Using a linear rail for consistent sample introduction, the three isomers of each type were analyzed 96 times over an eight-week timespan. The classification methods investigated included a univariate approach, the Welch t test at each included ion; a multivariate approach, linear discriminant analysis; and a machine learning approach, the Random Forest classifier. For each method, multiple validation techniques were used including restricting the classifier to data that was only generated on one day. Of these classification methods, the Random Forest algorithm was ultimately the most accurate and robust, consistently achieving out-of-bag error rates below 5%. At an inconclusive rate of approximately 5%, a success rate of 100% was obtained for isomer identification when applied to a randomly selected test set. The model was further tested with data acquired as a part of a different batch. The highest classification success rate was 93.9%, and error rates under 5% were consistently achieved.

Tee-Shaped Sample Introduction Device Coupled with Direct Analysis in Real-Time Mass Spectrometry for Gaseous Analytes

Ambient ionization mass spectrometry (AIMS) is simple to operate for analytes adsorbed on the surface of various shaped probes. However, gaseous substances or liquids that are easy to evaporate, diffuse, and escape in the atmosphere are harder to capture. In this work, a Tee-shaped sample introduction device coupled with direct analysis in real time mass spectrometry (DART-MS) is developed. The Tee-shaped device is placed between the DART ion source and the MS inlet with a heated sample transfer tube. Gaseous samples from either a Tedlar sampling bag or liquids evaporated from a graduated syringe were tested. The Tee-shaped device was used for several volatile organic compounds with a wide range of boiling points, and detection limits of ng/mL to fg/mL were obtained. To test the device for real-life samples, puff-by-puff analysis of a complex gaseous mainstream smoke was performed. Individual puffs can be analyzed rapidly, and there is no cross contamination between consecutive puffs. The dynamic changes of chemical components among different puffs for different types of cigarettes can be observed. This work provides a universal Tee-shaped sampling device to enhance AIMS for the analysis of volatile compounds and gases, which is adapted to different sampling modules applicable for various forms of samples. The device enables direct exploration of chemical components in complex gaseous samples without tedious sample preparation and time-consuming LC or GC separation.

Rapid Analysis of Volatile Phenols from Grape Juice by Immersive Sorbent Sheet Extraction Prior to Direct Analysis in Real-Time Mass Spectrometry (DART-MS)

Poly(dimethylsiloxane)-based thin-film sorbent sheets (SPMESH) have previously been used for parallel headspace (HS) extraction prior to direct analysis in real-time mass spectrometry (DART-MS) for rapid quantitation of odorants in complex matrices. However, HS-SPMESH extraction is poorly suited for less volatile odorants, e.g., volatile phenols. This report describes modifications to the previous SPMESH extraction device, which make it amenable to parallel extraction of low-volatility analytes from multiwell plates under direct immersion (DI) conditions. Optimization and validation of the DI-SPMESH-DART-MS approach were performed on four volatile phenols (4-ethylphenol, 4-ethylguaiacol, 4-methylguaiacol, and guaiacol) of relevance to the quality of grape juices. Negative-ion mode DART-MS spectra showed a series of oxygenated adducts [M + nO - H]^- for all analytes, but isobaric interferences could be limited for three of the four analytes by selecting an appropriate MS/MS transition. Signal suppression from nonvolatiles (sugars, acids) could be overcome by a rinse step. DI-SPMESH-DART-MS analysis of 24 samples could be performed in ∼45 min (30 min extraction, 16 min DART analysis) with 0.5-3 μg/L detection limits in aqueous and model juice solutions. In real grape juices (n = 5 cultivars), good accuracy (72-137%) could be achieved for two of the four volatile phenols initially investigated, 4-ethylphenol and 4-ethylguaiacol. However, poor accuracy was observed for guaiacol in some cultivars, and 4-methylguaiacol could not be quantitated due to interferences with other volatile phenols. Despite these limitations, DI-SPMESH-DART-MS/MS may be useful for prescreening a large number of samples prior to more selective conventional analyses.

Rapid fingerprint analysis for herbal polysaccharides using direct analysis in real-time ionization mass spectrometry

RATIONALE

Herbal polysaccharides have various potential medicinal values. Development of reliable analytical method for the fingerprint analysis of polysaccharides is critical for their quality assessment, origin identification, and authenticity evaluation.

METHODS

Mechanochemical extraction (MCE) was used to extract polysaccharide components from different herbal species. Intact polysaccharides were then directly analyzed by direct analysis in real-time mass spectrometry (DART-MS). Standard addition method with isotope-labeled internal standard was used to quantify polysaccharide amounts directly from liquid extract. Multivariate data analysis was further conducted for species classification.

RESULTS

The intact and large polysaccharides were decomposed into small fragment ions less than m/z 350 instantaneously using DART ion source. Different polysaccharides showed distinguished fingerprint DART-MS spectra using both individual and mixed herbal species. The liquid supernatant from MCE was validated to be used as direct sample for DART-MS analysis. Quantitation was successfully achieved for polysaccharide contents in Dendrobium officinale from different locations.

CONCLUSIONS

A rapid fingerprint protocol in combination of MCE and DART-MS for herbal polysaccharides was developed. The whole process could be accomplished within a few minutes, from raw materials to final spectra, without requirements of pre-digestion and additional sample purification.

Forensic applications of DART-MS: A review of recent literature

The need for rapid chemical analyses and new analytical tools in forensic laboratories continues to grow due to case backlogs, difficult-to-analyze cases, and identification of previously unseen materials such as new psychoactive substances. To adapt to these needs, the forensics community has been pursuing the use of ambient ionization mass spectrometry, and more specifically direct analysis in real time mass spectrometry (DART-MS), for a wide range of applications. From the inception of DART-MS forensic applications have been researched with demonstrations ranging from drugs of abuse to inorganic gunshot residue to printer inks to insect identification. This article presents a review of research demonstrating the use of DART-MS for forensically relevant samples over the past five years. To provide more context, background on the technique, sampling approaches, and data analysis methods are presented along with a discussion on the potential future and research needs of the technology.

Analysis of food samples made easy by microextraction technologies directly coupled to mass spectrometry

Because of the complexity and diversity of food matrices, their chemical analysis often entails several analytical challenges to attain accurate and reliable results, especially for multiresidue analysis and ultratrace quantification. Nonetheless, microextraction technology, such as solid-phase microextraction (SPME), has revolutionized the concept of sample preparation for complex matrices because of its nonexhaustive, yet quantitative extraction approach and its amenability to coupling to multiple analytical platforms. In recent years, microextraction devices directly interfaced with mass spectrometry (MS) have redefined the analytical workflow by providing faster screening and quantitative methods for complex matrices. This review will discuss the latest developments in the field of food analysis by means of microextraction approaches directly coupled to MS. One key feature that differentiates SPME-MS approaches from other ambient MS techniques is the use of matrix compatible extraction phases that prevent biofouling, which could drastically affect the ionization process and are still capable of selective extraction of the targeted analytes from the food matrix. Furthermore, the review examines the most significant applications of SPME-MS for various ionization techniques such as direct analysis in real time, dielectric barrier desorption ionization, and some unique SPME geometries, for example, transmission mode SPME and coated blade spray, that facilitate the interface to MS instrumentation.

Polymeric Sorbent Sheets Coupled to Direct Analysis in Real Time Mass Spectrometry for Trace-Level Volatile Analysis-A Multi-Vineyard Evaluation Study

Etched polymeric sorbent sheets (solid-phase mesh-enhanced sorption from headspace (SPMESH) sheets) were recently described as an alternative to solid-phase microextraction (SPME) for rapid, parallel, multi-sample extraction and pre-concentration of headspace volatiles. In this report, a workflow was evaluated based on SPMESH sheet extraction followed by direct analysis in real time-mass spectrometry (DART-MS) using grape samples harvested from multiple commercial vineyards at different maturities. SPMESH sheet-DART-MS(-MS) was performed on two grape-derived odorants related to wine quality: 3-isobutyl-2-methoxypyrazine (IBMP) in Cabernet Sauvignon and Merlot grape homogenate (n = 86 samples) and linalool in Muscat-type grape juice samples (n = 18 samples). As part of the optimization process, an MS-MS method was developed for IBMP and an equilibration procedure prior to extraction was established for homogenate samples. Following optimization, we achieved good correlation between SPMESH sheet-DART-MS and SPME-GC-MS for both IBMP (range by GC-MS = < 2 ng/L to 28 ng/L, R² = 0.70) and linalool (range by GC-MS = 135 to 415 μg/L, R² = 0.66). The results indicate SPMESH sheet-DART-MS is suitable for rapid measurements of trace level volatiles in grapes.

Spatially Resolved Headspace Extractions of Trace-Level Volatiles from Planar Surfaces for High-Throughput Quantitation and Mass Spectral Imaging

The use of headspace thin-film microextraction devices (SPMESH) for parallel extraction of trace-level volatiles prior to direct analysis in real-time mass spectrometry (DART-MS) has been reported previously, in which volatiles were extracted from samples in multi-well plates. In this report, we demonstrate that headspace extraction of volatiles by SPMESH sheets can be performed directly from planar surfaces. When coupled with DART-MS, this approach yields volatile mass spectral images with at least 4 mm resolution. When samples were spotted onto general-purpose silica gel thin-layer chromatography (TLC) plates, the SPMESH extraction could reach equilibrium within 2-4 min and 48 samples could be extracted and analyzed in 14 min. Because volatilization of analytes from TLC plates was very rapid, SPMESH extraction was delayed by the addition of 5% polyethylene glycol. Good linearity was achieved in the microgram per liter to milligram per liter range for four odorants (3-isobutyl-2-methoxypyrazine, linalool, methyl anthranilate, and o-aminoacetophenone) in several matrices (water, 10% ethanol, juice, and grape macerate) using 5 μL sample sizes. Detection limits as low as 50 pg/spot (10 μg/L in grape macerate) could be achieved. In contrast to many reports on headspace solid-phase microextraction, negligible matrix effects were observed for ethanol and grape macerates compared to water. SPMESH can preserve volatile images from planar surfaces, and SPMESH-DART-MS from TLC plates is well-suited for rapid trace volatile analysis, especially with small sample sizes.

High-throughput quantification of drugs of abuse in biofluids via 96-solid-phase microextraction-transmission mode and direct analysis in real time mass spectrometry

RATIONALE

The workload of clinical laboratories has been steadily increasing over the last few years. High-throughput (HT) sample processing allows scientists to spend more time undertaking matters of critical thinking rather than laborious sample processing. Herein we introduce a HT 96-solid-phase microextraction (SPME) transmission mode (TM) system coupled to direct analysis in real time (DART) mass spectrometry (MS).

METHODS

Model compounds (opioids) were extracted from urine and plasma samples using a 96-SPME-TM device. A standard voltage and pressure (SVP) DART source was used for all experiments. Examination of SPME-TM performance was done using high-resolution mass spectrometry (HRMS) in full scan mode (100-500 m/z), whereas quantitation of opioids was performed using triple quadrupole MS in multiple reaction monitoring mode and by using a matrix-matched internal standard correction method.

RESULTS

Thirteen points (0.5 to 200 ng mL^-1 ) were used to establish a calibration curve. Low limits of quantitation (LOQ) were obtained (0.5 to 25 ng mL^-1 ) for matrices used. Acceptable accuracy (71.4-129.4%) and repeatability (1.1-24%) were obtained for validation levels tested (0.5, 30 and 90 ng mL^-1 ). In less than 1.5 hours, 96 samples were extracted, desorbed and processed using the 96-SPME-TM system coupled to DART-MS.

CONCLUSIONS

A rapid HT method for detection of opioids in urine and plasma samples was developed. This study demonstrated that ambient ionization mass spectrometry coupled to robust sample preparation methods such as SPME-TM can rapidly and efficiently screen/quantify target analytes in a HT context.

Dispersive Magnetic Solid-Phase Extraction Coupled to Direct Analysis in Real Time Mass Spectrometry for High-Throughput Analysis of Trace Environmental Contaminants

Coupling dispersive magnetic solid-phase extraction (DMSPE) to direct analysis in real time mass spectrometry (DART-MS) with a newly developed metal iron probe enables high-throughput, sensitive detection of herbicides such as triazine in environmental waters. Magnetic graphene oxide was used as a dispersive sorbent because it increased adsorption capacity in the DMSPE process. The planar structure and excellent thermal conductivity of graphene oxide facilitated the desorption and ionization of target analytes in DART-MS analysis. The iron probe, which is designed to fit into the moving trail of the DART interface, served as the sorbent collector as well as the support for the magnetic graphene oxide after DMSPE, and was put directly into the DART system. The ratio of magnetic core to graphene oxide in the nanoparticles and other key parameters in DMSPE and DART-MS procedures were systematically investigated and optimized. In addition, the presence of water on the sorbent proves to have a significant effect on DART-MS analysis. No organic solvents are used in this method, and the reusable iron probe is of low cost. Under the optimal conditions, limits of detection were found in the range of 1.6-152.1 ng/L for the triazines. Recovery and reproducibility were found to be in the ranges of 87.5-115.0% and 1.9-10.2%, respectively, for the six herbicides studied. The analytical performance of the DMSPE-DART-MS method indicated that applications for trace analysis of other compounds in liquid samples are also possible.

Development, Optimization and Applications of Thin Film Solid Phase Microextraction (TF-SPME) Devices for Thermal Desorption: A Comprehensive Review

Through the development of solid phase microextraction (SPME) technologies, thin film solid phase microextraction (TF-SPME) has been repeatedly validated as a novel sampling device well suited for various applications. These applications, encompassing a wide range of sampling methods such as onsite, in vivo and routine analysis, benefit greatly from the convenience and sensitivity TF-SPME offers. TF-SPME, having both an increased extraction phase volume and surface area to volume ratio compared to conventional microextraction techniques, allows high extraction rates and enhanced capacity, making it a convenient and ideal sampling tool for ultra-trace level analysis. This review provides a comprehensive discussion on the development of TF-SPME and the applications it has provided thus far. Emphasis is given on its application to thermal desorption, with method development and optimization for this desorption method discussed in detail. Moreover, a detailed outlook on the current progress of TF-SPME development and its future is also discussed with emphasis on its applications to environmental, food and fragrance analysis.

Ambient desorption/ionization mass spectrometry: evolution from rapid qualitative screening to accurate quantification tool

In this article, some recent trends and developments in ambient desorption/ionization mass spectrometry (ADI-MS) are reviewed, with a special focus on quantitative analyses with direct, open-air sampling. Accurate quantification with ADI-MS is still not routinely performed, but this aspect is considered of utmost importance for the advancement of the field. In fact, several research groups are devoted to the development of novel and optimized ADI-MS approaches. Some key trends include novel sample introduction strategies for improved reproducibility, tailored sample preparation protocols for removing the matrix and matrix effects, and multimode ionization sources. In addition, there is significant interest in quantitative mass spectrometry imaging. Graphical abstract Conceptual diagram of the ambient desorption/ionization mass spectrometry approach with different desorption/ionization probes.

Analysis of Trace Drugs of Abuse by Direct Analysis in Real Time (DART) Mass Spectrometry

Analysis of trace amounts of drugs of abuse is important in a variety of situations, including forensic casework. Here, a method for the facile, rapid collection of traces of drugs from a variety of porous and nonporous surfaces, including fabrics, is detailed. A small amount of extraction solvent, including an internal standard, is applied to the fabric surface, followed by application of a patterned absorbent disk which resorbs much of the extraction solvent along with dissolved traces of any drug present. Over half of the extraction solvent is recovered in 15 s from many natural and synthetic fabrics, with weights ranging from 64 to 374 mg/in.², by pressing a half-inch diameter patterned glass fiber membrane disk to the wetted area. The patterned disk is then placed in a standard OpenSpot™ holder of a direct analysis in real time (DART) mass spectrometer with a data collection time of 1 or 2 min. Semi-quantitation of low microgram levels of drugs is achieved by comparison of spectra to those from a standard control disk.

Internal Extractive Electrospray Ionization Mass Spectrometry for Quantitative Determination of Fluoroquinolones Captured by Magnetic Molecularly Imprinted Polymers from Raw Milk

Antibiotics contamination in food products is of increasing concern due to their potential threat on human health. Herein solid-phase extraction based on magnetic molecularly imprinted polymers coupled with internal extractive electrospray ionization mass spectrometry (MMIPs-SPE-iEESI-MS) was designed for the quantitative analysis of trace fluoroquinolones (FQs) in raw milk samples. FQs in the raw milk sample (2 mL) were selectively captured by the easily-lab-made magnetic molecularly imprinted polymers (MMIPs), and then directly eluted by 100 µL electrospraying solvent biased with +3.0 kV to produce protonated FQs ions for mass spectrometric characterization. Satisfactory analytical performance was obtained in the quantitative analysis of three kinds of FQs (i.e., norfloxacin, enoxacin, and fleroxacin). For all the samples tested, the established method showed a low limit of detection (LOD ≤ 0.03 µg L⁻¹) and a high analysis speed (≤4 min per sample). The analytical performance for real sample analysis was validated by a nationally standardized protocol using LC-MS, resulting in acceptable relative error values from −5.8% to +6.9% for 6 tested samples. Our results demonstrate that MMIPs-SPE-iEESI-MS is a new strategy for the quantitative analysis of FQs in complex biological mixtures such as raw milk, showing promising applications in food safety control and biofluid sample analysis.

Trace-Level Volatile Quantitation by Direct Analysis in Real Time Mass Spectrometry following Headspace Extraction: Optimization and Validation in Grapes

Ambient ionization mass spectrometric (AI-MS) techniques like direct analysis in real time (DART) offer the potential for rapid quantitative analyses of trace volatiles in food matrices, but performance is generally limited by the lack of preconcentration and extraction steps. The sensitivity and selectivity of AI-MS approaches can be improved through solid-phase microextraction (SPME) with appropriate thin-film geometries, for example, solid-phase mesh-enhanced sorption from headspace (SPMESH). This work improves the SPMESH-DART-MS approach for use in food analyses and validates the approach for trace volatile analysis for two compounds in real samples (grape macerates). SPMESH units prepared with different sorbent coatings were evaluated for their ability to extract a range of odor-active volatiles, with poly(dimethylsiloxane)/divinylbenzene giving the most satisfactory results. In combination with high-resolution mass spectrometry (HRMS), detection limits for SPMESH-DART-MS under 4 ng/L in less than 30 s acquisition times could be achieved for some volatiles [3-isobutyl-2-methoxypyrazine (IBMP) and β-damascenone]. A comparison of SPMESH-DART-MS and SPME-GC-MS quantitation of linalool and IBMP demonstrates excellent agreement between the two methods for real grape samples (r² ≥ 0.90), although linalool measurements appeared to also include isobaric interference.

Towards on-site analysis of complex matrices by solid-phase microextraction-transmission mode coupled to a portable mass spectrometer via direct analysis in real time

On-site analysis of complex matrices by SPME-TM coupled to a portable mass spectrometer via DART.