Ambient sampling/ionization mass spectrometry: applications and current trends

Protein analysis by desorption electrospray ionization mass spectrometry

This review presents progress made in the ambient analysis of proteins, in particular by desorption electrospray ionization-mass spectrometry (DESI-MS). Related ambient ionization techniques are discussed in comparison to DESI-MS only to illustrate the larger context of protein analysis by ambient ionization mass spectrometry. The review describes early and current approaches for the analysis of undigested proteins, native proteins, tryptic digests, and indirect protein determination through reporter molecules. Applications to mass spectrometry imaging for protein spatial distributions, the identification of posttranslational modifications, determination of binding stoichiometries, and enzymatic transformations are discussed. The analytical capabilities of other ambient ionization techniques such as LESA and nano-DESI currently exceed those of DESI-MS for in situ surface sampling of intact proteins from tissues. This review shows, however, that despite its many limitations, DESI-MS is making valuable contributions to protein analysis. The challenges in sensitivity, spatial resolution, and mass range are surmountable obstacles and further development and improvements to DESI-MS is justified.

Recent developments and applications of ambient mass spectrometry imaging in pharmaceutical research: an overview

The application of ambient mass spectrometry imaging "MSI" is expanding in the areas of fundamental research on drug delivery and multiple phases of the process of identifying and developing drugs. Precise monitoring of a drug's pharmacological workflows, such as intake, distribution, metabolism, and discharge, is made easier by MSI's ability to determine the concentrations of the initiating drug and its metabolites across dosed samples without losing spatial data. Lipids, glycans, and proteins are just a few of the many phenotypes that MSI may be used to concurrently examine. Each of these substances has a particular distribution pattern and biological function throughout the body. MSI offers the perfect analytical tool for examining a drug's pharmacological features, especially in vitro and in vivo effectiveness, security, probable toxic effects, and putative molecular pathways, because of its high responsiveness in chemical and physical environments. The utilization of MSI in the field of pharmacy has further extended from the traditional tissue examination to the early stages of drug discovery and development, including examining the structure-function connection, high-throughput capabilities in vitro examination, and ex vivo research on individual cells or tumor spheroids. Additionally, an enormous array of endogenous substances that may function as tissue diagnostics can be scanned simultaneously, giving the specimen a highly thorough characterization. Ambient MSI techniques are soft enough to allow for easy examination of the native sample to gather data on exterior chemical compositions. This paper provides a scientific and methodological overview of ambient MSI utilization in research on pharmaceuticals.

Recent Developments in the Detection of Organic Contaminants Using Molecularly Imprinted Polymers Combined with Various Analytical Techniques

Molecularly imprinted polymers (MIPs) encompass a diverse array of polymeric matrices that exhibit the unique capacity to selectively identify a designated template molecule through specific chemical moieties. Thanks to their pivotal attributes, including exceptional selectivity, extended shelf stability, and other distinct characteristics, this class of compounds has garnered interest in the development of highly responsive sensor systems. As a result, the incorporation of MIPs in crafting distinctive sensors and analytical procedures tailored for specific analytes across various domains has increasingly become a common practice within contemporary analytical chemistry. Furthermore, the range of polymers amenable to MIP formulation significantly influences the potential utilization of both conventional and innovative analytical methodologies. This versatility expands the array of possibilities in which MIP-based sensing can be employed in recognition systems. The following review summarizes the notable progress achieved within the preceding seven-year period in employing MIP-based sensing techniques for analyte determination.

Surface-Coated Acupuncture Needles as Solid-Phase Microextraction Probes for In Vivo Analysis of Bioactive Molecules in Living Plants by Mass Spectrometry

In this work, we report the coupling of solid-phase microextraction (SPME) enabled by surface-coated acupuncture needles with nano-electrospray mass spectrometry (nanoESI-MS) for the analysis of bioactive molecules in living plants. The needle tip was oxidized by a mixture of nitric acid and hydrogen peroxide solution and then subject to surface coating via carbonization of paraffin. A combination of oxidation and surface coating resulted in a thin coating of carbon film, whereby the significantly increased surface area promoted both analyte enrichment and ionization for MS analysis. The analytical performances were evaluated through the characterization of small molecules, peptides and proteins. Compared with conventional nanoESI, our new strategy of employing surface-coated needles had a high salt tolerance. The streamlined experimental workflow could be completed within one minute. The linear dynamic ranges for L-histidine and L-lysine, as two representatives, were over two orders of magnitude with a limit of detection (LOD) of 3.0~5.0 ng/mL. A mark is made on the needle at 2 mm from the tip, the needle is then kept in the sample for 30 s. In vivo sampling and identification of α-tomatine and organic acids from the stem of a living tomato plant were demonstrated as a practical application, while the physiological activities of the plant were not disrupted due to the minimally invasive sampling. We anticipate that the developed strategy may be of potential use for real-time clinical and other on-site analyses.

Influence of host-guest interactions on analytical performance of direct analysis in real-time mass spectrometry

To systematically study the influence of host-guest interactions on the analytical performance of direct analysis in real time mass spectrometry (DART-MS), the interactions between cyclodextrins (CDs) and different Sudan dyes were investigated. The results showed that the host-guest interaction between CDs and Sudan dyes did not affect qualitative analysis of the target compounds, but led to a lower signal intensity for Sudan dyes, thus affecting quantitative analysis of the target compounds. The stronger the host-guest interaction, the weaker the signal intensity of target compound on DART-MS. The results also show that both in solution and in solid-phase microextraction (SPME), the addition of organic solvents can weaken the host-guest interaction between CDs and Sudan dyes, thus improving the signal intensity in DART-MS. In SPME, adding organic solvents has a certain practical value and can improve the efficiency of Sudan dye analysis. This study suggests that appropriate sample pretreatment is needed to weaken noncovalent interactions prior to DART-MS analysis to obtain more accurate quantitative results. The data provide some insight into the effects of other noncovalent interactions on the efficiency of DART-MS as an analytical tool, as well as the potential to study intermolecular interactions with DART-MS.

In vitro: Anti-coccidia activity of Calotropis procera leaf extract on Eimeria papillata oocysts sporulation and sporozoite

Natural products play an important role as environmentally friendly agents that can be used against parasitic diseases. Many Eimeria species cause eimeriosis in poultry. The negative effects of synthetic anti-coccidiosis medications necessitate the quest for alternative treatments derived from medicinal plants in the treatment of eimeriosis. The study was conducted to evaluate the effects of Calotropis procera leaf extract (CPLE) (Madar) on the sporulation of Eimeria oocysts and sporozoites that affect mammalian jejunum and to obtain the best concentration for sporulation inhibition and infection prevention. Extracts were tested in vitro to prevent oocyst sporulation, wall deformity, and anti-sporozoite activity with Eimeria papillata. The plant-chemical compounds analysis of CPLE some active compounds were shown as well as CPLE in vitro effects at various concentrations (200, 100, 50, 25,12.5, and 6.25 mg/mL), while potassium dichromate solution 2.5% and Toltrazuril 25 mg/mL were administered as the control groups. C. procera leaf extract showed the highest inhibitory percentage on E. papillata oocyst at 200 mg/mL of extract, approximately 91%. In addition, CPLE showed the sporozoite highest viability inhibitory percentage on E. papillata at 200 mg/mL of extract, approximately 88%, and the lowest efficacy was 5% at 6.25 mg/mL. Also, we noticed the deformation and destruction of the oocyst wall based on the concentration rate. Sporulation inhibition rate is significantly affected by incubation time and treatment concentration ratio. The results showed that Madar has an effective, inhibitory potential, and protective effect on coccidian oocyst sporulation and sporozoites of E. papillata.

Deeper Understanding of Solvent-Based Ambient Ionization Mass Spectrometry: Are Molecular Profiles Primarily Dictated by Extraction Mechanisms?

Solvent-based ambient ionization mass spectrometry (MS) techniques provide a powerful approach for direct chemical analysis and molecular profiling of biological tissues. While molecular profiling of tissues has been widely used for disease diagnosis, little is understood about how the interplay among solvent properties, matrix effects, and ion suppression can influence the detection of biological molecules. Here, we perform a systematic investigation of the extraction processes of lipids using an ambient ionization droplet microsampling platform to investigate how the physicochemical properties of the solvent systems and extraction time influence molecular extraction and detection. Direct molecular profiling and quantitative liquid chromatography-mass spectrometry (LC-MS) of discrete solvent droplets after surface sampling were investigated to provide insights into extraction and ionization mechanisms. The results of this study suggest that intermolecular interactions such as hydrogen bonding play a major role in extraction and detection of lipids using solvent-based ambient ionization techniques. In addition, extraction time was observed to impact the molecular profiles obtained, suggesting optimization of this parameter can be performed to favor detection of specific analytes.

Ambient Ionization Mass Spectrometry: Application and Prospective

Mass spectrometry (MS) is a formidable analytical tool for the analysis of non-polar to polar compounds individually and/or from mixtures, providing information on the molecular weights and chemical structures of the analytes. During the last more than one-decade, ambient ionization mass spectrometry (AIMS) has developed quickly, producing a wide range of platforms and proving scientific improvements in a variety of domains, from biological imaging to quick quality control. These methods have made it possible to detect target analytes in real time without sample preparation in an open environment, and they can be connected to any MS system with an atmospheric pressure interface. They also have the ability to analyze explosives, illicit drugs, disease diagnostics, drugs in biological samples, adulterants in food and agricultural products, reaction progress, and environmental monitoring. The development of novel ambient ionization techniques, such as probe electrospray ionization, paper spray ionization, and fiber spray ionization, employed even at picolitre to femtolitre solution levels to provide femtogram to attogram levels of the target analytes. The special characteristic of this ambient ion source, which has been extensively used, is the noninvasive property of PESI of examination of biological real samples. The results in the current review supports the idea that AIMS has emerged as a pioneer in MS-based approaches and that methods will continue to be developed along with improvements to existing ones in the near future.

Using an insulating fiber as the sampling probe and ionization substrate for ambient ionization-mass spectrometric analysis of volatile, semi-volatile, and polar analytes

A sharp metal needle used as the ionization emitter in conventional atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) is usually required for analyte ionization through corona discharge (i.e., gas discharge). Nevertheless, we herein demonstrate that an insulating fiber (tip diameter: 10-60 µm; length: ~ 1 cm) made of glass or bamboo can function as an APCI-like ionization emitter. Although no direct electric contact is made on the fiber, the ionization of volatiles and semi-volatiles occurs when the fiber is placed close (~ 1 mm) to the inlet of the mass spectrometer. No analyte ion signals can be observed without placing the insulating fiber in front of the mass spectrometer. The generation of ion species mainly relies on the electric field provided by the mass spectrometer. Presumably, owing to the high electric field provided by the mass spectrometer, the dielectric breakdown voltages of gas molecules in the air and the fiber are overcome, leading to the ionization of analytes in gas phase. In addition, the insulating fiber can function as a holder for sample solutions. Electrospray ionization-like processes derived from polar analytes such as amino acids, peptides, and proteins can readily occur when the insulating fiber deposited with a sample droplet is placed close to the inlet of the mass spectrometer. The feasibility of using the current approach for the detection of nonpolar and polar analytes from complex fetal bovine serum samples without tedious sample pretreatment is demonstrated in this work. The main advantage of using the suggested fiber is that the fiber can be used as the sampling probe to pick up samples and placed in front of a mass spectrometer for direct MS analysis. The application of using a robust, insulating, and disposable probe to pick up samples from real samples such as onion, honey, and pork samples followed by direct MS analysis is also demonstrated.

Contemporary Research Progress on the Detection of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are a class of the most common and widespread contaminants. The accumulation of PAHs has made a certain impact on the environment and is seriously threatening human health. Numerous general analytical methods suitable for PAHs were developed. With the development of economy, the environmental problems of PAHs in modern society are more extensive and prominent, and attract more attention from environmental scientists and analysts. Deeper understanding of the properties of PAHs depends on the advent of detection methods, which can also be more conducive to promoting the protection of the environment. Till now, more sensitive, more high-speed and more high-throughput analytical tools are being invented and have played important roles in the research of PAHs. In this short review article, we focused mainly on the contemporary analytical methods about PAHs. We started with a brief review on the hazards, migration, distribution and traditional analysis methods of PAHs in recent years, including liquid chromatography, gas chromatography, surface enhanced Raman spectroscopy and so on. We also presented the applications of the modern ambient mass spectrometry, especially microwave plasma torch mass spectrometry, in the detection of PAHs, as well as the far out novel results in our lab by using microwave plasma torch (MPT) mass spectrometry; for example, some new insights about Birch reduction, regular hydrogen addition and the robustness of molecular structure. These studies have demonstrated the versatility of MPT MS as a platform in the research of PAHs.

Molecular Pathological Diagnosis of Thyroid Tumors Using Spatially Resolved Metabolomics

The pathological diagnosis of benign and malignant follicular thyroid tumors remains a major challenge using the current histopathological technique. To improve diagnosis accuracy, spatially resolved metabolomics analysis based on air flow-assisted desorption electrospray ionization mass spectrometry imaging (AFADESI-MSI) technique was used to establish a molecular diagnostic strategy for discriminating four pathological types of thyroid tumor. Without any specific labels, numerous metabolite features with their spatial distribution information can be acquired by AFADESI-MSI. The underlying metabolic heterogeneity can be visualized in line with the cellular heterogeneity in native tumor tissue. Through micro-regional feature extraction and in situ metabolomics analysis, three sets of metabolic biomarkers for the visual discrimination of benign follicular adenoma and differentiated thyroid carcinomas were discovered. Additionally, the automated prediction of tumor foci was supported by a diagnostic model based on the metabolic profile of 65 thyroid nodules. The model prediction accuracy was 83.3% when a test set of 12 independent samples was used. This diagnostic strategy presents a new way of performing in situ pathological examinations using small molecular biomarkers and provides a model diagnosis for clinically indeterminate thyroid tumor cases.

Recent advances in nanomaterials for prostate cancer detection and diagnosis

Despite the significant progress in the discovery of biomarkers and the exploitation of technologies for prostate cancer (PCa) detection and diagnosis, the initial screening of these PCa-related biomarkers using current...

Ionization of Volatile Organics and Nonvolatile Biomolecules Directly from a Titanium Slab for Mass Spectrometric Analysis

Atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) and electrospray ionization (ESI)-MS can cover the analysis of analytes from low to high polarities. Thus, an ion source that possesses these two ionization functions is useful. Atmospheric surface-assisted ionization (ASAI), which can be used to ionize polar and nonpolar analytes in vapor, liquid, and solid forms, was demonstrated in this study. The ionization of analytes through APCI or ESI was induced from the surface of a metal substrate such as a titanium slab. ASAI is a contactless approach operated at atmospheric pressure. No electric contacts nor any voltages were required to be applied on the metal substrate during ionization. When placing samples with high vapor pressure in condensed phase underneath a titanium slab close to the inlet of the mass spectrometer, analytes can be readily ionized and detected by the mass spectrometer. Furthermore, a sample droplet (~2 μL) containing high-polarity analytes, including polar organics and biomolecules, was ionized using the titanium slab. One titanium slab is sufficient to induce the ionization of analytes occurring in front of a mass spectrometer applied with a high voltage. Moreover, this ionization method can be used to detect high volatile or polar analytes through APCI-like or ESI-like processes, respectively.

Faster, better, and cheaper: harnessing microfluidics and mass spectrometry for biotechnology

High-throughput screening technologies are widely used for elucidating biological activities. These typically require trade-offs in assay specificity and sensitivity to achieve higher throughput. Microfluidic approaches enable rapid manipulation of small volumes and have found a wide range of applications in biotechnology providing improved control of reaction conditions, faster assays, and reduced reagent consumption. The integration of mass spectrometry with microfluidics has the potential to create high-throughput, sensitivity, and specificity assays. This review introduces the widely-used mass spectrometry ionization techniques that have been successfully integrated with microfluidics approaches such as continuous-flow system, microchip electrophoresis, droplet microfluidics, digital microfluidics, centrifugal microfluidics, and paper microfluidics. In addition, we discuss recent applications of microfluidics integrated with mass spectrometry in single-cell analysis, compound screening, and the study of microorganisms. Lastly, we provide future outlooks towards online coupling, improving the sensitivity and integration of multi-omics into a single platform.

A fast and direct determination of bisphenol S in thermal paper samples using paper spray ionization mass spectrometry

Concerns about human health regarding the large use of bisphenol A in thermal papers have led to its replacement by bisphenol S. Analyses of bisphenols require several sample pretreatment steps, which are laborious, expensive, and time-consuming. A paper spray ionization mass spectrometry (PSI-MS) was developed to detect and quantify bisphenol S in three different brands of thermal papers commercially available. Parameters such as paper size, and paper position relative to the mass spectrometer inlet were evaluated. The analyses were performed in selected ion monitoring mode on a linear ion trap mass spectrometer. The developed method presented absolute recovery values ranging from 92.2 to 109.04%, accuracy values from -1.2 to 9.0%, and inter assay precision from 1.8 to 5.6% and enabled LOD as low as 5 ng g^-1. The concentration of bisphenol S in all of the three brands of BPA-free thermal papers evaluated ranged from 1.36 to 6.77 μg g^-1, and the concentrarion of BPA ranged from 6.56 to 16.4 μg g^-1 in all samples of thermal paper evaluated. The PSI-MS method described here was comparable to the conventional ones, such as liquid chromatography coupled with mass spectrometry and gas chromatography coupled with mass spectrometry described in the literature. The present study proved to be practical, fast, and efficient for the direct determination of bisphenol S in thermal papers. Furthermore, the methodology here described showed to be a promising alternative to replace the classical methods for determination of bisphenol S, due to its simplicity, and no needing of any sample pretreatment.

Laser assisted sampling vs direct desorption flowing atmospheric pressure afterglow mass spectrometry of complex polymer samples: Forensic implications for pressure sensitive tape chemical analysis

Flowing atmospheric pressure afterglow (FAPA) mass spectrometry (MS) is an easy-to-use, cost-effective, and potentially portable technique that allows direct desorption/ionization from samples with little-to-no sample preparation for real-time chemical analysis. However, it has limitations regarding analytes with low desorption efficiency, such as polymers. Here, laser assisted sampling (LAS) is developed and coupled to FAPA MS to allow access to a wider range of chemical information from polymer samples. This is achieved through laser-induced pyrolysis conditions that provide a much higher degree of spatio-temporal control compared to typical pyrolysis techniques. LAS FAPA MS, together with direct desorption FAPA MS, is implemented on pressure sensitive adhesive (PSA) tape samples, which are often found at crime scenes and recovered as forensic evidence. Comparative PSA tape examination is typically performed to assess any differences in the comparison of unknown and known samples and provide an evidentiary association between suspects and crime scenes in forensic applications. PSA tape samples from several manufacturers of duct, masking, and electrical tape were analyzed from the adhesive and backing side. Direct desorption FAPA provides top-surface selectivity and the tape mass spectra are dominated by more peaks at lower m/z, many of which correspond to polymer additives. LAS gives access to sampling from all of the tape layers and the FAPA mass spectra is extended to higher m/z, while polymer fragmentation patterns are evident. Principal components analysis (PCA) was implemented to assess the ability of each technique to distinguish and categorize identified tape classes within the sampled population. The complementary nature of the resulting mass spectra from direct desorption vs LAS FAPA was evident from the PCA as different tape brands sub-sets were discriminated by each technique. The differentiation obtained by combining both methods is already competitive, or better, than conventional techniques, with the additional benefits of AMS.

Modernization of Control of Pathogenic Micro-Organisms in the Food-Chain Requires a Durable Role for Immunoaffinity-Based Detection Methodology-A Review

Food microbiology is deluged by a vastly growing plethora of analytical methods. This review endeavors to color the context into which methodology has to fit and underlines the importance of sampling and sample treatment. The context is that the highest risk of food contamination is through the animal and human fecal route with a majority of foodborne infections originating from sources in mass and domestic kitchens at the end of the food-chain. Containment requires easy-to-use, failsafe, single-use tests giving an overall risk score in situ. Conversely, progressive food-safety systems are relying increasingly on early assessment of batches and groups involving risk-based sampling, monitoring environment and herd/flock health status, and (historic) food-chain information. Accordingly, responsible field laboratories prefer specificity, multi-analyte, and high-throughput procedures. Under certain etiological and epidemiological circumstances, indirect antigen immunoaffinity assays outperform the diagnostic sensitivity and diagnostic specificity of e.g., nucleic acid sequence-based assays. The current bulk of testing involves therefore ante- and post-mortem probing of humoral response to several pathogens. In this review, the inclusion of immunoglobulins against additional invasive micro-organisms indicating the level of hygiene and ergo public health risks in tests is advocated. Immunomagnetic separation, immunochromatography, immunosensor, microsphere array, lab-on-a-chip/disc platforms increasingly in combination with nanotechnologies, are discussed. The heuristic development of portable and ambulant microfluidic devices is intriguing and promising. Tant pis, many new platforms seem unattainable as the industry standard. Comparability of results with those of reference methods hinders the implementation of new technologies. Whatever the scientific and technological excellence and incentives, the decision-maker determines this implementation after weighing mainly costs and business risks.

Rapid Evaporative Ionization Mass Spectrometry: A Review on Its Application to the Red Meat Industry with an Australian Context

The red meat supply chain is a complex network transferring product from producers to consumers in a safe and secure way. There can be times when fragmentation can arise within the supply chain, which could be exploited. This risk needs reduction so that meat products enter the market with the desired attributes. Rapid Evaporative Ionisation Mass Spectrometry (REIMS) is a novel ambient mass spectrometry technique originally developed for rapid and accurate classification of biological tissue which is now being considered for use in a range of additional applications. It has subsequently shown promise for a range of food provenance, quality and safety applications with its ability to conduct ex vivo and in situ analysis. These are regarded as critical characteristics for technologies which can enable real-time decision making in meat processing plants and more broadly throughout the sector. This review presents an overview of the REIMS technology, and its application to the areas of provenance, quality and safety to the red meat industry, particularly in an Australian context.

Helium-Plasma-Ionization Mass Spectrometry of Metallocenes and Their Derivatives

Ferrocene and its derivatives and nickelocene undergo facile ionization when exposed directly to the ionizing plasma of a helium-plasma ionization (HePI) source. Mass spectra recorded from such samples under ambient positive-ion-generating conditions show intense peaks for the respective molecular ions [M^+•] and protonated species [(M + H)⁺]. The protonation process occurs most efficiently when traces of water are present in the heated nitrogen used as the "heating gas." In fact, the relative population of the two categories of ions generated in this way can be manipulated by regulating the heating-gas flow. Moreover, rapid and highly efficient gas-phase hydrogen-deuterium exchange (HDX) reactions can be performed in the ion source by passing the heating gas through a vial with D₂O before it reaches the HePI source. Moreover, the ionized species generated in this way can be subjected to in-source CID fragmentation in the QDa-HePI source very efficiently by varying the sampling-cone voltage. By this procedure, ions generated from ferrocene and nickelocene could be stripped so far as to ultimately generate the bare-metal cation. Other typical fragment-ions produced from protonated metallocenes included the M(cp)₁⁺ ions (M = Fe or Ni), by elimination of a cyclopentadiene molecule, or the molecular cation, by loss of a H^• radical. Moreover, H/D exchanges and subsequent tandem mass spectrometric analysis indicated that the central metal core participates in the initial protonation process of ferrocene under HePI conditions. However, in compounds such as ferrocene carboxaldehyde and ferrocene boronic acid, the protonation takes place at the peripheral functional group.

Accelerated nucleophilic substitution reactions of dansyl chloride with aniline under ambient conditions via dual-tip reactive paper spray

Paper spray ionization (PSI) mass spectrometry (MS) is an emerging tool for ambient reaction monitoring via microdroplet reaction acceleration. PSI-MS was used to accelerate and monitor the time course of the reaction of dansyl chloride with aniline, in acetonitrile, to produce dansyl aniline. Three distinct PSI arrangements were explored in this study representing alternative approaches for sample loading and interaction; conventional single tip as well as two novel setups, a dual-tip and a co-axial arrangement were designed so as to limit any on-paper interaction between reagents. The effect on product abundance was investigated using these different paper configurations as it relates to the time course and distance of microdroplet travel. It was observed that product yield increases at a given distance and then decreases thereafter for all PSI configurations. The fluorescent property of the product (dansyl aniline) was used to visually inspect the reaction progress on the paper substrate during the spraying process. Amongst the variety of sample loading methods the novel dual-tip arrangement showed an increased product yield and microdroplet density, whilst avoiding any on-paper interaction between the reagents.

Solvent-free, Noncontact Electrostatic Sampling for Rapid Analysis with Mass Spectrometry: Application to Drugs and Explosives

A hand-held Van de Graaf generator is used to apply a high voltage, negligible current electrostatic potential to a wire mesh positioned in close proximity to a particle-laden surface in order to collect those particles for analysis. The electrostatic field effects transfer particles to the mesh without a requirement for mechanical contact between mesh and surface. Analysis of chemicals present in the sampled particles is completed by thermal desorption electrospray ionization. The utility of the method for noncontact sampling is demonstrated using solid drug powder samples, and inorganic explosives dispersed either on solid surfaces or in sand/soil in order to simulate common interfering matrices that might be encountered in the forensic environment. A metal mesh sampling substrate is utilized instead of traditional polymer-based swabs in order to permit thermal desorption at higher temperatures. The method leaves no visible trace of sampling leaving details such as a fingerprint image unperturbed, as demonstrated using fluorescence photography. Direct sampling of trace particles from hard surfaces and skin documents flexibility in the choice of sampling substrates, desorption temperatures, and sampling times. The potential of the device for use in forensic analyses is detailed.

Ambient (desorption/ionization) mass spectrometry methods for pesticide testing in food: a review

Ambient mass spectrometry refers to the family of techniques that allows ions to be generated from condensed phase samples under ambient conditions and then, collected and analysed by mass spectrometry. One of their key advantages relies on their ability to allow the analysis of samples with minimal to no sample workup. This feature maps well to the requirements of food safety testing, in particular, those related to the fast determination of pesticide residues in foods. This review discusses the application of different ambient ionization methods for the qualitative and (semi)quantitative determination of pesticides in foods, with the focus on different specific methods used and their ionization mechanisms. More popular techniques used are those commercially available including desorption electrospray ionization (DESI-MS), direct analysis on real time (DART-MS), paper spray (PS-MS) and low-temperature plasma (LTP-MS). Several applications described with ambient MS have reported limits of quantitation approaching those of reference methods, typically based on LC-MS and generic sample extraction procedures. Some of them have been combined with portable mass spectrometers thus allowing "in situ" analysis. In addition, these techniques have the ability to map surfaces (ambient MS imaging) to unravel the distribution of agrochemicals on crops.

Evaluating bioanalytical capabilities of paper spray ionization for abiraterone drug quantification in patient plasma

Paper spray ionization (PSI) is a direct, fast, and low-cost ambient ionization technique which may have clinical utility for qualitative and quantitative analysis of therapeutic drugs and metabolites from patient specimens. We developed and validated a PSI-mass spectrometry (PSI-MS/MS) method according to the US-FDA guidelines for bioanalytical studies to measure the prostate cancer drug abiraterone directly from patient plasma. The established linearity range was 3.1-156.8 ng/mL with a precision (%CV) and an accuracy (%) range of 0.5-10.7 and 93.5-103.2, respectively. The mean internal standard normalized matrix factor for abiraterone was just below 1 with highest %CV of 10.2 at the low-level quality control. In benchmarking the performance of this assay against a published LC-MS/MS assay, we showed they were mostly equivalent, with the exception of accuracy with clinical samples. We found the quantitative values observed for abiraterone measured directly from patient plasma using PSI-MS/MS showed positive bias. Upon investigation, we concluded the increased values were due to summed quantitation of isomeric abiraterone conjugates and metabolites which are separable by LC-MS/MS, but not with the current PSI-MS/MS configuration. Despite demonstrating the utility of PSI-MS/MS for rapid bioanalysis, this study also highlighted a limitation encountered with the direct analysis of abiraterone in clinical samples.

MASS SPECTROMETRY ANALYSIS OF DRUGS OF ABUSE: CHALLENGES AND EMERGING STRATEGIES

Mass spectrometry has been the "gold standard" for drugs of abuse (DoA) analysis for many decades because of the selectivity and sensitivity it affords. Recent progress in all aspects of mass spectrometry has seen significant developments in the field of DoA analysis. Mass spectrometry is particularly well suited to address the rapidly proliferating number of very high potency, novel psychoactive substances that are causing an alarming number of fatalities worldwide. This review surveys advancements in the areas of sample preparation, gas and liquid chromatography-mass spectrometry, as well as the rapidly emerging field of ambient ionization mass spectrometry. We have predominantly targeted literature progress over the past ten years and present our outlook for the future. © 2020 Periodicals, Inc. Mass Spec Rev.

Simple and rapid nicotine analysis using a disposable silica nanochannel-assisted electrochemiluminescence sensor

Nicotine analysis is essential to medicine, toxicology and the tobacco industry. However, no simple, portable and disposable method was developed to meet their demands. Here, we report a simple, rapid and disposable silica nanochannel (SAN)-based electrochemiluminescence (ECL) sensor for nicotine analysis by simply assembling a SAN electrode with a paper cover. The sensing principle of the disposable sensor is based on the size exclusion effect and charge selectivity, which obviously prolong the sensor service time. We find that the sensor exhibits good specificity to nicotine, and most of the complex matrices are unlikely to impact the detection. The performance of the disposable sensor in cigarettes, e-cigarettes, nicotine gums, and lozenges is fully validated, showing satisfactory linearity, sensitivity (a limit of detection of 27.82 nM), and accuracy (a recovery between 96.00% and 106.51%). The disposable sensor can be potentially applied for on-site nicotine analysis.

Wire Desorption Combined with Electrospray Ionization Mass Spectrometry: Direct Analysis of Small Organic and Large Biological Compounds

A novel atmospheric pressure ionization mass spectrometry based on wire desorption and electrospray ionization (WD-ESI) for direct analysis was developed to characterize chemical compounds with different polarities and thermal stabilities at atmospheric pressure. This technique is a variant of the thermal desorption electrospray ion source developed by Shiea et al. One large improvement is that the heating speed (>500 °C/s) of the thermal desorption in this work is extremely fast, using a self-heating metal wire, with which sample solution can splash from the surface to form small droplets and thus the analytes can be protected from thermal decomposition. With this feature, we have successfully achieved soft ionization of highly polar organic and biological compounds such as aflatoxin, small peptides, and even large proteins from complex matrices. The simple structure and self-cleaning capability of the WD-ESI source make it ideal for on-site screening in various applications such as food safety and biodrug testing, especially when coupled with a transportable mass spectrometer.

Recent advances of ambient ionization mass spectrometry imaging in clinical research

The structural information and spatial distribution of molecules in biological tissues are closely related to the potential molecular mechanisms of disease origin, transfer, and classification. Ambient ionization mass spectrometry imaging is an effective tool that provides molecular images while describing in situ information of biomolecules in complex samples, in which ionization occurs at atmospheric pressure with the samples being analyzed in the native state. Ambient ionization mass spectrometry imaging can directly analyze tissue samples at a fairly high resolution to obtain molecules in situ information on the tissue surface to identify pathological features associated with a disease, resulting in the wide applications in pharmacy, food science, botanical research, and especially clinical research. Herein, novel ambient ionization techniques, such as techniques based on spray and solid-liquid extraction, techniques based on plasma desorption, techniques based on laser desorption ablation, and techniques based on acoustic desorption were introduced, and the data processing of ambient ionization mass spectrometry imaging was briefly reviewed. Besides, we also highlight recent applications of this imaging technology in clinical researches and discuss the challenges in this imaging technology and the perspectives on the future of the clinical research.

Analysis of non-conjugated steroids in water using paper spray mass spectrometry

A novel strategy for the direct analysis of non-conjugated steroids in water using paper spray mass spectrometry (PS-MS) has been developed. PS-MS was used in the identification and quantification of non-conjugated (free) steroids in fish tank water samples. Data shown herein indicates that individual amounts of free steroids can be detected in aqua as low as; 0.17 ng/µL, 0.039 ng/µL, 0.43 ng/µL, 0.0076 ng/µL for aldosterone, corticosterone, cortisol, and β-estrone, respectively, and with an average relative standard deviation of ca. < 10% in the positive ion mode using PS-MS/MS. Direct detection of free steroids in a raw water mixture, from aquaculture, without prior sample preparation is demonstrated. The presence of free steroids released in fish water samples was confirmed via tandem mass spectrometry using collision-induced dissociation. This approach shows promise for rapid and direct water quality monitoring to provide a holistic assessment of non-conjugated steroids in aqua.

Rapid determination of chemical composition in the particulate matter of cigarette mainstream smoke

Particulate matter from mainstream smoke (MSS) is significantly hazardous when inhaled into the human body. An ambient ionization mass spectrometric method, direct analysis in real time mass spectrometry (DART-MS), was applied to rapidly and simultaneously measure multiple particulate components in MSS. A variety of compounds were obtained in seconds, where different types of cigarettes and different solvent extracts generated distinct chemical constituents as validated by principle component analysis. Chemical formula assignment and compound identification were based on accurate m/z values with mass errors <10 ppm. Quantitation of nicotine was achieved using an isotope internal standard with DART-MS. Method validation with chromatographic-MS analysis further proved the advantages of DART-MS with respect to analysis speed and operational simplicity for the direct evaluation of complex samples. DART-MS is feasible for the rapid acquisition of cigarette fingerprints for quality control as well as for quantitative assessment of carcinogens for harm reduction.

Rapid quantification of acetaminophen in plasma using solid-phase microextraction coupled with thermal desorption electrospray ionization mass spectrometry

RATIONALE

Solid-phase microextraction coupled with thermal desorption electrospray ionization tandem mass spectrometry (SPME-TD-ESI-MS/MS) is proposed as a novel method for the rapid quantification of acetaminophen in plasma samples from a pharmacokinetics (PK) study.

METHODS

Traces of acetaminophen were concentrated on commercial fused-silica fibers coated with a polar polyacrylate (PA) polymer using direct immersion SPME. No agitation, heating, addition of salt, or adjustment of the pH of the sample solution was applied during the extraction. Any acetaminophen absorbed on the SPME fibers was subsequently desorbed and detected by TD-ESI-MS/MS.

RESULTS

Parameters of the absorption, sensitivity, reproducibility, and linearity for the SPME-TD-ESI-MS/MS method were evaluated. The time required to complete a TD-ESI-MS/MS analysis was less than 30 seconds. Matrix-matching calibration was performed to calculate the concentration of acetaminophen in the sample. A linear calibration curve with a concentration range of 100-10,000 ng/mL was constructed to calculate the quantity of acetaminophen. The SPME-TD-ESI-MS quantification results for acetaminophen in plasma were in good agreement with those obtained by the conventional LC/MS/MS method.

CONCLUSIONS

With the proposed method, a 10-min SPME time was enough to achieve the lower limit of quantitation (i.e. 100 ng/mL) and for a complete PK profiling of acetaminophen. A shorter extraction time could be achieved by applying agitation, heating, adding salt, or adjusting the pH of the sample solution to enhance analyte absorption efficiency. The time required to detect acetaminophen on the SPME fiber was less than 30 s, allowing the rapid quantification of acetaminophen in plasma with good accuracy.

Study on properties of wooden capillary electrospray ionization mass spectrometry

RATIONALE

In view of the unique properties of wooden materials as electrospray emitters, a novel wooden capillary electrospray ionization (WC-ESI) device was fabricated. The performance of a wooden capillary as an electrospray emitter was investigated by using a wooden capillary instead of the metal emitter of commercial ESI sources.

METHODS

The mass spectrometric measurement of baicalein, emodin and myoglobin was carried out by using wooden capillary (WC) and metal capillary (MC) ESI sources. Contrasting analysis of signal intensity between WC and MC electrospray ionization mass spectrometry (ESI-MS) was implemented at different sample flow rates. The effect of WC-ESI-MS and MC-ESI-MS was evaluated experimentally with electrospray solutions in different solvent ratios.

RESULTS

Generally, the signal generated by WC-ESI-MS was much stronger than that obtained by MC-ESI-MS. In particular, the MS signal in negative ion mode was very strong, which may solve the long-standing problem of low MS signals in negative ion mode, and fully improve the detection efficiency of ESI-MS.

CONCLUSIONS

The signal intensity produced by WC-ESI-MS is significantly higher than that from MC-ESI-MS, and polymerization and electrolysis are reduced; therefore, the spectra become simpler. In addition, it is also tolerant to high flow rates and high aqueous phase samples.

Mass spectrometry as a tool to advance polymer science

In contrast to natural polymers, which have existed for billions of years, the first well-understood synthetic polymers date back to just over one century ago. Nevertheless, this relatively short period has seen vast progress in synthetic polymer chemistry, which can now afford diverse macromolecules with varying structural complexities. To keep pace with this synthetic progress, there have been commensurate developments in analytical chemistry, where mass spectrometry has emerged as the pre-eminent technique for polymer analysis. This Perspective describes present challenges associated with the mass-spectrometric analysis of synthetic polymers, in particular the desorption, ionization and structural interrogation of high-molar-mass macromolecules, as well as strategies to lower spectral complexity. We critically evaluate recent advances in technology in the context of these challenges and suggest how to push the field beyond its current limitations. In this context, the increasingly important role of high-resolution mass spectrometry is emphasized because of its unrivalled ability to describe unique species within polymer ensembles, rather than to report the average properties of the ensemble.

Large-Area Triboelectric Nanogenerator Mass Spectrometry: Expanded Coverage, Double-Bond Pinpointing, and Supercharging

Efficient ionization is a necessary condition for mass spectrometric analysis, but many compounds fail to ionize well enough to yield sufficient detection limits. Triboelectric nanogenerators (TENG) coupled to nanoelectrospray ionization (nanoESI) mass spectrometry (MS) are a highly effective approach to high sensitivity MS analysis. Here, we report on new, large-area TENG that constructively leverage the relationship between electrode size, created charges, and open-circuit voltage, leading to wider chemical coverage. Large-area TENG were found to also promote electrospray gas-phase oxidation reactions that enabled double bond position pinpointing for unsaturated lipids and species-specific lipid quantitation. Furthermore, large-area TENG MS of proteins was observed to yield higher charge state distributions (i.e., supercharging) without the need for high surface tension additives.

Exploiting the native inspiratory ability of a mass spectrometer to improve analysis efficiency

In this study, a new approach to perform self-aspirating sampling in mass spectrometry (MS) analysis was developed by using the native inspiratory ability of a mass spectrometer. Specifically, the inspiratory channel and sampling inlet of the MS instrument were integrated into a single pathway through a sealed ionization chamber to facilitate analyte delivery and improve sample utilization. Based on this approach, combined with structural simplification and optimization, a versatile electrospray ionization (ESI) source has been constructed and characterized using different mass spectrometers. In addition to the self-aspirating ability, this source configuration can provide sub-ambient pressure (SAP) conditions for ionization, which were conducive to suppressing the background ions generated from some air-involved reactions. Moreover, it can also be used directly for electrospray-driven extraction ionization. With the SAP-ESI source, a conventional mass spectrometer enables rapid analysis of both volatiles and solutions via secondary electrospray ionization and coaxial electrospray ionization, respectively. As the compact gas pathway of the source will promote the efficient transfer and ionization of the sampled substances, the total consumption of the analyte for each analysis can be reduced to subnanogram level and a subppbv limit detection is achieved. Other demonstrated features such as the versatility, easy operation as well as simple assembly will likely contribute to the prevalence of the proposed sampling and ionization strategy.

In this study, a new approach to perform self-aspirating sampling in mass spectrometry (MS) analysis was developed by using the native inspiratory ability of a mass spectrometer.

Potential of Recent Ambient Ionization Techniques for Future Food Contaminant Analysis Using (Trans)Portable Mass Spectrometry

In food analysis, a trend towards on-site testing of quality and safety parameters is emerging. So far, on-site testing has been mainly explored by miniaturized optical spectroscopy and ligand-binding assay approaches such as lateral flow immunoassays and biosensors. However, for the analysis of multiple parameters at regulatory levels, mass spectrometry (MS) is the method of choice in food testing laboratories. Thanks to recent developments in ambient ionization and upcoming miniaturization of mass analyzers, (trans)portable mass spectrometry may be added to the toolkit for on-site testing and eventually compete with multiplex immunoassays in mixture analysis. In this study, we preliminary evaluated a selection of recent ambient ionization techniques for their potential in simplified testing of selected food contaminants such as pesticides, veterinary drugs, and natural toxins, aiming for a minimum in sample preparation while maintaining acceptable sensitivity and robustness. Matrix-assisted inlet ionization (MAI), handheld desorption atmospheric pressure chemical ionization (DAPCI), transmission-mode direct analysis in real time (TM-DART), and coated blade spray (CBS) were coupled to both benchtop Orbitrap and compact quadrupole single-stage mass analyzers, while CBS was also briefly studied on a benchtop triple-quadrupole MS. From the results, it can be concluded that for solid and liquid sample transmission configurations provide the highest sensitivity while upon addition of a stationary phase, such as in CBS, even low μg/L levels in urine samples can be achieved provided the additional selectivity of tandem mass spectrometry is exploited.

Tissue classification by rapid evaporative ionization mass spectrometry (REIMS): comparison between a diathermic knife and CO2 laser sampling on classification performance

The increasing need for rapid, in situ, and robust tissue profiling approaches in the context of intraoperative diagnostics has led to the development of a large number of ambient ionization-based surface sampling strategies. This paper compares the performances of a diathermic knife and a CO2 laser handpiece, both clinically approved, coupled to a rapid evaporative ionization mass spectrometry (REIMS) source for quasi-instantaneous tissue classification. Several fresh meat samples (muscle, liver, bone, bone marrow, cartilage, skin, fat) were obtained from different animals. Overall, the laser produced cleaner cuts and more reproducible and higher spectral quality signals when compared with the diathermic knife (CV laser = 9-12%, CV diathermic = 14-23%). The molecular profiles were subsequently entered into a database and PCA/LDA classification/prediction models were built to assess if the data generated with one sampling modality can be employed to classify the data generated with the other handpiece. We demonstrate that the correct classification rate of the models increases (+ 25%) with the introduction of a model based on peak lists that are tissue-specific and common to the two handpieces, compared with considering solely the whole molecular profile. This renders it possible to use a unique and universal database for quasi-instantaneous tissue recognition which would provide similar classification results independent of the handpiece used. Furthermore, the laser was able to generate aerosols rich in lipids from hard tissues such as bone, bone marrow, and cartilage. Combined, these results demonstrate that REIMS is a valuable and versatile tool for instantaneous identification/classification of hard tissue and coupling to different aerosol-generating handpieces expands its field of application. Graphical abstract.

1,4-Benzoquinone as a Highly Efficient Dopant for Enhanced Ionization and Detection of Nitramine Explosives on a Single-Quadrupole Mass Spectrometer Fitted with a Helium-Plasma Ionization (HePI) Source

Previous investigations have evaluated the efficacy of anions such as NO₃^-, Cl^-_, Br^-, CH₃COO^-, and CF₃COO^- as additives to generate or enhance mass spectrometric signals from explosives under plasma ionization conditions. The results of this study demonstrate that for detecting nitramine-class explosives, such as 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX), 1,4-benzoquinone (BQ) is a highly effective and efficient dopant. When used in conjunction with ambient-pressure negative-ion helium-plasma ionization (HePI), 1,4-benzoquinone readily captures an electron, forming an abundant molecular anion (m/z 108), which upon exposure to vapors of RDX and HMX generates adduct ions of m/z 330 and 404, respectively. The signal level recorded for RDX upon adduction to the radical anion of 1,4-benzoquinone under our experimental conditions was significantly higher than that realized by chloride adduction using dichloromethane (DCM) as the dopant.

Ion Manipulation in Open Air Using 3D-Printed Electrodes

Ambient ionization techniques provide a way to sample materials via creation of ions in the air. However, transferring and focusing of these ions is typically done in the reduced pressure environment of the mass spectrometer. Spray-based ambient ionization sources require relatively large distances between the source and mass spectrometer inlet for effective desolvation, resulting in a small fraction of the ions being collected. To increase the efficiency of ion transfer from atmosphere to vacuum, 3D-printed focusing devices made of conductive carbon nanotube doped polymers have been designed and evaluated for ion focusing in air. Three main classes of electrodes are considered: (i) conic section electrodes (conical, ellipsoidal, and cylindrical), (ii) simple conductive and non-conductive apertures, and (iii) electrodes with complex geometries (straight, chicane, and curved). Simulations of ion trajectories performed using the statistical diffusion simulation (SDS) model in SIMION showed a measure of agreement with experiment. Cross-sectional images of ion beams were captured using an ion detecting charge-coupled device (IonCCD). After optimization, the best arrangements of electrodes were coupled to an Agilent Ultivo triple quadrupole to record mass spectra. Observations suggest that electrode geometry strongly influences ion trajectories in air. Non-conductive electrodes also assisted in focusing, due to charge buildup from ion deposition. We also observed minimal spreading of the ion packet after exiting the focusing electrodes indicating that atmospheric collisions do not reduce collimation of the beam. The study suggests that high pressures need not be viewed as a hindrance to ion transport, but as a potentially useful force.

Tools for the Quality Control of Pharmaceutical Heparin

Heparin is a vital pharmaceutical anticoagulant drug and remains one of the few naturally sourced pharmaceutical agents used clinically. Heparin possesses a structural order with up to four levels of complexity. These levels are subject to change based on the animal or even tissue sources that they are extracted from, while higher levels are believed to be entirely dynamic and a product of their surrounding environments, including bound proteins and associated cations. In 2008, heparin sources were subject to a major contamination with a deadly compound-an over-sulphated chondroitin sulphate polysaccharide-that resulted in excess of 100 deaths within North America alone. In consideration of this, an arsenal of methods to screen for heparin contamination have been applied, based primarily on the detection of over-sulphated chondroitin sulphate. The targeted nature of these screening methods, for this specific contaminant, may leave contamination by other entities poorly protected against, but novel approaches, including library-based chemometric analysis in concert with a variety of spectroscopic methods, could be of great importance in combating future, potential threats.