Effect of internal and external conditions on ionization processes in the FAPA ambient desorption/ionization source

Quantitative analysis of biopolymers in lignocellulosic biomass feedstocks via laser-assisted micro-pyrolysis flowing atmospheric-pressure afterglow high-resolution ambient mass spectrometry

Herein, a diode laser-assisted micro-pyrolysis (LAMP) technique coupled with FAPA high resolution mass spectrometry (HRMS) is demonstrated for fast chemical characterization of lignocellulosic biomass feedstocks. The solid lignocellulosic biomass can be analyzed directly with minimal sample preparation. The mass spectra of the pyrolysis products are interpreted with the aid of data visualization tools such as Kendrick mass defect (KMD) plots and van Krevelen plots. Furthermore, quantitation of lignin/cellulose/hemicellulose, sugar contents of glucan/xylan/galactan/arabinan and lignin monomeric unit S/G is achieved with good accuracy and precision, through multivariate analysis methods, including partial least squares regression (PLSR) and support vector regression (SVR).

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.

Instantaneous Differentiation of Functional Isomers via Reactive Flowing Atmospheric Pressure Afterglow Mass Spectrometry

Ambient mass spectrometry (AMS) allows direct desorption and ionization of analytes in real time with minimal-to-no sample preparation. However, it may present inadequate capabilities for differentiating isomers. Here, a reactive flowing atmospheric-pressure afterglow (reactive-FAPA) AMS source is developed for rapid isomer differentiation by derivatization of analytes in real time. The effects of the reactive-FAPA operating conditions on the reagent and product ions were studied and optimized for highly volatile and non-volatile model compounds with different carbonyl functional groups. In addition, two functional isomers of valproic acid (VPA) metabolites, 4-ene VPA and γ-valprolactone, are successfully differentiated for the first time by incorporating methylamine (MA) reagent vapor into the plasma effluent used for desorption/ionization. Reactive-FAPAMS for 4-ene VPA shows only detectable peaks of the protonated acylation product [M + MA-H₂O + H]⁺, while for γ-valprolactone, it shows detectable peaks for both protonated acylation product [M + MA-H₂O + H]⁺ and protonated intermediate [M + MA + H]⁺. A method for quantitative characterization of mixtures of 4-ene VPA and γ-valprolactone is also developed and validated. In addition, reactive-FAPAMS also shows better detection sensitivity compared to nonreactive-FAPAMS for some larger analyte types, such as UV filters and steroids. The limit of detection (LOD) of pregnenolone acetate in reactive-FAPAMS is 310 ng/mL, which is about 10 times better than its LOD in nonreactive-FAPA.

Interpretation of Ionization Mechanism Responsible for Reagent Ion and Analyte Formation in Microwave-Induced Plasma Desorption Ionization Mass Spectrometry

Ambient desorption/ionization (ADI) sources coupled to mass spectrometer have gained increasing interest in the field of analytical chemistry for its fast and direct analysis of samples. Among many ADI sources, plasma-based ADI sources are an important branch. Despite its extensive use in mass spectrometry analysis, the ionization mechanism of these sources still remain uncertain. The study on ionization mechanism is of great significance to optimize the design of ion sources and to improve ionization efficiency. In this study, targeted research on a better understanding of afterglow distance effects on ionization process was conducted. Based on the quantified signal expression of reagent ions in mass spectrum, the concept that optimal atmospheric analysis distance of plasma ADI source is defined for the first time. From the perspective of mutual restriction effect between atmospheric components, the formation progress of reagent ions was visually revealed in detail, which involved the initial step of forming precursor reagent ions, the clusters reaction for increasing production of reagent ions, and the matrix effect results in reagent ion depletion. The formation mechanism of reagent ions further clarified the explicit reason for abundant reagent ions generated at an optimal distance. Most importantly, the analyte analysis results verified the significant impact of appropriate distance on ionization efficiency in afterglow region. It was confirmed that the quantity and type of reagent ions intimately influenced the status of analyte ions in mass spectrum.

Plasma-Based Ambient Desorption/Ionization Mass Spectrometry for the Analysis of Liquid Crystals Employed in Display Devices

Liquid-crystal displays (LCDs) are the most frequently used display technology worldwide these days. Due to the rather complex manufacturing process and purity requirements for the chemicals used, quality control and display failure analysis are important analytical tasks. Currently, the state-of-the-art techniques (e.g., high-performance liquid chromatography (HPLC), gas chromatography (GC) coupled to mass spectrometry (MS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), or high-resolution microscopy) are costly and time-consuming. Hence, a new pathway to precisely analyze liquid-crystalline materials and LCDs in their native state is reported. A new approach for direct analysis via plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) offers an inexpensive and faster alternative. In this study, direct analysis in real time (DART), the low-temperature plasma (LTP) probe, and flowing atmospheric-pressure afterglow (FAPA) ADI sources coupled to high-resolution mass spectrometry (HR-MS) are compared based on their capabilities and performance for liquid-crystal analysis. These sources enable direct analyte desorption from a sample surface at ambient conditions and ionize the vaporized analyte molecules in a subsequent step. Primarily, the ionization capabilities of the three ADI sources are compared for individual liquid-crystal standards, mixtures of liquid crystals (LCs), and complex liquid crystal/additive mixtures applied in commercially available LCDs. Furthermore, direct surface analysis from a glass substrate is also performed with ADI-MS to compare their applicability to this type of sample matrix.

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.

Exploration and performance evaluation of microwave-induced plasma with different discharge gases for ambient desorption/ionization mass spectrometry

RATIONALE

Microwave-induced plasma (MIP) with different discharge gases of argon or helium provides significant plasma-based ambient desorption/ionization sources, which have potential applicability in direct analysis of complex samples without any sample pre-treatment. In this study, experiments were conducted to better understand microwave-induced plasma desorption/ionization (MIPDI) sources and the corresponding ionization mechanisms.

METHODS

Emission spectra of microwave-induced argon (MIP-Ar) and helium (MIP-He) plasmas were obtained from the plasma tail flame of a MIP source. Compounds including L-phenylalanine, L-serine, L-valine, urea, 4-acetaminophen, gallic acid and L-ascorbic acid were analyzed using both sources. Polyethylene glycol 400 (PEG400) oligomers were detected by MIP-Ar and MIP-He mass spectrometry at different microwave powers. Mass spectra of higher molecular weight PEGs (including PEG800, PEG1000 and PEG2000) were also acquired using both sources.

RESULTS

In the emission spectra, N₂ , H-I and O-I species were observed by MIP-Ar/He. In addition, SiO₂ , Na-I, Si-I and Si-II species were generated by MIP-He. In the mass spectra of compounds, [M+H]⁺ , [2M+H]⁺ , [M+O+H]⁺ , [M+2O-H]⁺ and fragment ions were observed. In the mass spectra of PEG400 obtained by MIP-Ar/He at different microwave powers, higher molecular weight oligomers could only be observed with higher microwave power. PEGs with molecular weights as high as 1000 Da were also successfully analyzed by MIPDI.

CONCLUSIONS

According to the different natures of the samples, either MIP-Ar or MIP-He can be chosen as a working ion source for mass spectrometry. The MIPDI source is potentially applicable to the analysis of compounds with high molecular weights, especially polymers with high degree of polymerization (such as PEG2000), which is a challenging issue for the traditional ambient ionization sources. Copyright © 2017 John Wiley & Sons, Ltd.

A flowing atmospheric pressure afterglow as an ion source coupled to a differential mobility analyzer for volatile organic compound detection

A FAPA is a good alternative to traditional ion mobility ionization sources.

Real-Time Analysis of Ambient Organic Aerosols Using Aerosol Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (AeroFAPA-MS)

Organic compounds contribute to a major fraction of atmospheric aerosols and have significant impacts on climate and human health. However, because of their chemical complexity, their measurement remains a major challenge for analytical instrumentation. Here we present the development and characterization of a new soft ionization technique that allows mass spectrometric real-time detection of organic compounds in aerosols. The aerosol flowing atmospheric-pressure afterglow (AeroFAPA) ion source is based on a helium glow discharge plasma, which generates excited helium species and primary reagent ions. Ionization of the analytes occurs in the afterglow region after thermal desorption and produces mainly intact quasimolecular ions, facilitating the interpretation of the acquired mass spectra. We illustrate that changes in aerosol composition and concentration are detected on the time scale of seconds and in the ng m(-3) range. Additionally, the successful application of AeroFAPA-MS during a field study in a mixed forest region is presented. In general, the observed compounds are in agreement with previous offline studies; however, the acquisition of chemical information and compound identification is much faster. The results demonstrate that AeroFAPA-MS is a suitable tool for organic aerosol analysis and reveal the potential of this technique to enable new insights into aerosol formation, growth, and transformation in the atmosphere.