Plasma-based ambient mass spectrometry: Recent progress and applications

Ambient mass spectrometry (AMS) has grown as a group of advanced analytical techniques that allow for the direct sampling and ionization of the analytes in different statuses from their native environment without or with minimum sample pretreatments. As a significant category of AMS, plasma-based AMS has gained a lot of attention due to its features that allow rapid, real-time, high-throughput, in vivo, and in situ analysis in various fields, including bioanalysis, pharmaceuticals, forensics, food safety, and mass spectrometry imaging. Tens of new methods have been developed since the introduction of the first plasma-based AMS technique direct analysis in real-time. This review first provides a comprehensive overview of the established plasma-based AMS techniques from their ion source configurations, mechanisms, and developments. Then, the progress of the representative applications in various scientific fields in the past 4 years (January 2017 to January 2021) has been summarized. Finally, we discuss the current challenges and propose the future directions of plasma-based AMS from our perspective.

LASER DESORPTION/ABLATION POSTIONIZATION MASS SPECTROMETRY: RECENT PROGRESS IN BIOANALYTICAL APPLICATIONS

Lasers have long been used in the field of mass spectrometric analysis for characterization of condensed matter. However, emission of neutrals upon laser irradiation surpasses the number of ions. Typically, only one in about one million analytes ejected by laser desorption/ablation is ionized, which has fueled the quest for postionization methods enabling ionization of desorbed neutrals to enhance mass spectrometric detection schemes. The development of postionization techniques can be an endeavor that integrates multiple disciplines involving photon energy transfer, electrochemistry, gas discharge, etc. The combination of lasers of different parameters and diverse ion sources has made laser desorption/ablation postionization (LD/API) a growing and lively research community, including two-step laser mass spectrometry, laser ablation atmospheric pressure photoionization mass spectrometry, and those coupled to ambient mass spectrometry. These hyphenated techniques have shown potentials in bioanalytical applications, with major inroads to be made in simultaneous location and quantification of pharmaceuticals, toxins, and metabolites in complex biomatrixes. This review is intended to provide a timely comprehensive view of the broadening bioanalytical applications of disparate LD/API techniques. We also have attempted to discuss these applications according to the classifications based on the postionization methods and to encapsulate the latest achievements in the field of LD/API by highlighting some of the very best reports in the 21st century. © 2020 John Wiley & Sons Ltd.

Rapid in-situ analysis of phthalates in face masks by desorption corona beam ionization tandem mass spectrometry

Phthalates (PAEs) are known as endocrine disruptors that can have adverse effects on human hormonal balance and development. Due to PAEs being semi-volatile chemical compounds, they can sustainably emit from the surfaces of objects containing PAEs. Face masks are commonly used to safeguard human health especially during periods of high prevalence of infectious diseases. As masks come into direct contact with the human respiratory system, PAEs from masks will enter the human body directly from the respiratory system thus potentially threatening human health. In this study, the desorption corona beam ionization (DCBI)-MS/MS method for the rapid in-situ detection of PAEs in face masks was established, which could perform ultra-fast, high-throughput identification and quantitative analysis on 13 kinds of PAEs, and the limits of detection (LODs) were 0.7 μg m^-2 for DAP, BBP, DBP, DPP, DHXP, DEHP, DINP and DDP, 1.4 μg m^-2 for DMEP, DEP, DPhP, DBEP and DNOP. Compared with the traditional liquid chromatography tandem mass spectrometry, this study shows that the DCBI-MS/MS method has the following advantages: 1) short analysis time, less than 1 min; 2) small solvent consumption, less than 10 μL; 3) the PAEs in face masks can be quickly in-situ screened.

Direct and quantitative in-situ analysis of third-hand smoke in and on various matrices by ambient desorption corona beam ionization mass spectrometry

Third-hand smoke (THS) is composed of surface-deposited remnants resulting from tabacco-smoking. Because THS components have properties of remaining on, re-emitting from and reacting on and with surfaces, in-situ analysis of the components on different surfaces is both in high demand and challenging. The aim of this study is to establish desorption corona beam ionization (DCBI)-MS/MS as an analytical tool for THS research. To this end, an in-situ DCBI-MS/MS approach was developed for the quantitative analysis of typical THS environmental markers, i.e. nicotine and cotinine on different surfaces such as fruits, cotton clothing, glass, and toys etc. The limits of detection of nicotine and cotinine were both 1.4 μg m-2. Low-temperature DCBI-MS/MS was applied to the direct detection of THS on fingers without any skin damage. Smoking-related biomarkers analyses in urine were accomplished, with a 10 s DCBI analysis time. The on-surface tobacco-specific nitrosamines (TSNAs), such as 1-(N-methyl-N-nitrosamino)-1-(3-pyridinyl)-4-butanal) (NNA), 4-(methylnitrosamino)-1-(3-pyridinyl)-1-butanone (NNK), and N-nitroso nornicotine (NNN) were in-situ successfully detected in dust samples.

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.

Ultrathin Homogenous AuNP Monolayers as Tunable Functional Substrates for Surface-Assisted Laser Desorption/Ionization of Small Biomolecules

A series of ultrathin, homogenous gold nanoparticle (AuNP) substrates for surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) were prepared using a simple air/water interface approach. These SALDI substrates enabled soft ionization and provided significant improvements in terms of signal intensities and reduced background levels in comparison to other AuNP morphologies for different analytes such as fatty acids, peptides, amino acids, saccharides, and drugs. Through different microscopic and spectroscopic methods, we determined that the packing homogeneity of the [AuNP]_n substrates played a vital role in the efficiency of the SALDI process. We demonstrated that the signal intensities of the investigated analytes were readily optimized by manipulating the thickness of the [AuNP]_n substrates. The desorption/ionization efficiency increased as a function of the number of layers and then reached a saturation point. The optimized [AuNP]_n substrates not only exhibited high SALDI-MS desorption/ionization efficiencies but also showed excellent reproducibilities of the analyte signals.

Ambient ionization MS for bioanalysis: recent developments and challenges

Ambient ionization MS has become very popular in analytical science and has now evolved as an effective analytical tool in metabolomics, biological tissue imaging, protein and small molecule drug analysis, where biological samples are probed in a rapid and direct fashion with minimal sample preparation at ambient conditions. However, certain inherent challenges continue to hinder the vibrant prospects of these methods for in situ analyses or to replace conventional methods in bioanalysis. This review provides an introduction to the field and its application in bioanalysis, with an emphasis on the most recent developments and applications. Furthermore, ongoing challenges or limitations related to quantitation, sensitivity, selectivity, instrumentation and mass range of these ambient methods will also be discussed.

Plasma-based ambient mass spectrometry techniques: The current status and future prospective

Plasma-based ambient mass spectrometry is emerging as a frontier technology for direct analysis of sample that employs low-energy plasma as the ionization reagent. The versatile sources of ambient mass spectrometry (MS) can be classified according to the plasma formation approaches; namely, corona discharge, glow discharge, dielectric barrier discharge, and microwave-induced discharge. These techniques allow pretreatment-free detection of samples, ranging from biological materials (e.g., flies, bacteria, plants, tissues, peptides, metabolites, and lipids) to pharmaceuticals, food-stuffs, polymers, chemical warfare reagents, and daily-use chemicals. In most cases, plasma-based ambient MS performs well as a qualitative tool and as an analyzer for semi-quantitation. Herein, we provide an overview of the key concepts, mechanisms, and applications of plasma-based ambient MS techniques, and discuss the challenges and outlook.

Direct analysis of quaternary alkaloids by in situ reactive desorption corona beam ionization MS

The direct detection of quaternary alkaloids by atmospheric pressure chemical ionization (APCI)-base ambient MS is difficult because of their poor volatility. In this study, a reactive protocol was developed for the in situ determination of quaternary alkaloids using desorption corona beam ionization (DCBI) mass spectrometry (MS). The model compounds of 8 quaternary alkaloids including sanguinarine, chelerythrine, cyclanoline, nitidine, coptisine, jatrorrhizine, berberine, palmatine and 2 tertiary alkaloids including protopine and allocryptopine were investigated in different states such as on a polytetrafluoroethylene (PTFE) plate, in raw herbal materials, and in silica gel. After various reactive reagents were studied, the mixture of saturated aqueous NaOH solution and CH3OH solvent (3 : 7, v/v) was selected as the optimized reactive reagent for the reactive DCBI-MS detection. All the target molecules can be detected with high sensitivity. On a PTFE plate the limits of detection were 0.0795, 0.1060, 0.4860, 0.9665, 0.8879, 0.3987, 0.5557, 0.4591, 0.0889, and 0.1929 mg L(-1) for sanguinarine, chelerythrine, cyclanoline, nitidine, coptisine, jatrorrhizine, berberine, palmatine, protopine, and allocryptopine, respectively. The reactive protocol was also applied to the direct detection of raw herbal materials and thin layer chromatography successfully.