A mechanism study of positive ionization processes in flowing atmospheric-pressure afterglow (FAPA) ambient ion source with controlled plasma and ambient conditions

Rapid analysis of pharmaceutical and personal care products by soft microwave-based plasma ionization-linear ion trap mass spectrometer (SMPI-LTQ) in natural water

In this study, a soft microwave plasma torch (SMPT) combined with a mass spectrometer (MS) was used for the first time as an analytical method to detect and analyze various pharmaceutical and personal care products (PPCPs) in aquatic environments without the need for sample pretreatment. For this purpose, ambient SMPT was used to generate plasma for ionizing the analyte molecules. Accordingly, nine PPCPs were identified by the SMPT-MS, and their identification was verified by collision-induced dissociation (CID). The technique's performance was verified with known PPCP samples, and the limits of detection (LOD) and quantification (LOQ) obtained over a linear range of 50-1 μg/L were 1.56 to 2.81 and 2.07 to 3.62 μg/L, respectively, with the standard addition recovery rate falling between 87.14 and 115.16%. These results show that the method has excellent sensitivity and selectivity, suggesting that SMPT can rapidly and directly detect PPCPs in environmental water, making it a promising method for rapid water quality inspection.

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.

Increasing DESI-MS Ion Signal by Plasma Treatment

Many studies are focused on using plasma in mass spectrometry as an ionization source or postionization method. In this study, the effect of plasma treatment in the sample preparation step of desorption electrospray ionization (DESI) has been investigated. The plasma treatment of polar samples, including morphine, codeine, captopril, theophylline, fructose, and amphiphilic compounds such as phosphatidylethanolamine (PE) in E. coli bacteria, as well as nonpolar compounds, including thebaine, papaverine, and noscapine, has been followed for ionization efficiency in DESI technique. An atmospheric-pressure glow discharge plasma (GDP) along with the electrospray ionization technique is examined. Plasma treatment before ambient ionization has a dramatic effect on polar and nonpolar sample signals in DESI-TOF mass spectrometry. The intensity of the mass spectrum shows an increase of 1.9-3.4 times for polar compounds, 2.1-2.5 times for nonpolar compounds, and 3.0 times for PE in E. coli bacteria (N = 4). Plasma is a source of reactive atoms, molecules, ions, radicals, and ultraviolet radiation. Plasma surface treatment before DESI analysis by energetic species through momentum/energy transfer yields higher energy surface molecules, leading to more/easier desorption. Under optimal treatment conditions, an improved ion signal intensity is observed without any fragmentation, decomposition, or chemical changes. Ion signals are increased possibly by both increased ionization through protonation of molecules and enhanced subsequent desorption during DESI analysis.

The Electrospray (ESI) and Flowing Atmosphere-Pressure Afterglow (FAPA) Mass Spectrometry Studies of Nitrophenols (Plant Growth Stimulants) Removed Using Strong Base-Functionalized Materials

The functional silica-based materials functionalized with a strong nitrogen base TBD (SiO₂-TBD) deposited via a linker or with a basic poly(amidoamine) dendrimer containing multiple terminal amine groups -NH₂ (SiO₂-EDA) and functional polymers containing a strong phosphazene base (Polymer-Phosphazene) or another basic poly(amidoamine) dendrimer (PMVEAMA-PAMAM) were tested as sorbents dedicated to a mixture of nitrophenols (p-nitrophenol and 2-methoxy-5-nitrophenol), which are analogs of nitrophenols used in plant growth biostimulants. The adsorptive potential of the studied materials reached 0.102, 0.089, 0.140, and 0.074 g of the nitrophenols g⁻¹, for SiO₂-TBD, SiO₂-EDA, polymer-phosphazene, and PMVEAMA-PAMAM, respectively. The sorptive efficiency of the analytes, i.e., their adsorption on the functional materials, the desorption from the obtained [(sorbent)H⁺ − nitrophenolates^–] complexes, and interactions with the used soil, were monitored using mass spectrometry (MS) technique with electrospray (ESI) and flowing atmosphere-pressure afterglow (FAPA) ionizations, for the analysis of the aqueous solutions and the solids, respectively. The results showed that the adsorption/desorption progress is determined by the structures of the terminal basic domains anchored to the materials, which are connected with the strength of the proton exchange between the sorbents and nitrophenols. Moreover, the conducted comprehensive MS analyses, performed for both solid and aqueous samples, gave a broad insight into the interactions of the biostimulants and the presented functional materials.

Methylation in combination with temperature programming enables rapid identification of polysaccharides by ambient micro-fabrication glow discharge plasma (MFGDP) desorption ionization mass spectrometry

Obtaining the fingerprints of polysaccharides was known to be notoriously difficult by ambient mass spectrometry due to their resistance for desorption and ionization. Ambient mass spectrometry technology has recently been recognized as a quick analysis tool for obtaining fingerprints, which is attributed to its characteristics of no sample pretreatment and easy operation under atmospheric pressure. However, it still remains a challenge for accurate identification of the fingerprints of macromolecular polysaccharides by ambient micro-fabrication glow discharge plasma (MFGDP). In this study, a simplified methylation method was introduced to realize rapid analysis of polysaccharide mixture by MFGDP with the assistance of a temperature-programmed system (TPS). At the optimal temperature of TPS, oligosaccharides, plant polysaccharides and polysaccharide mixtures were all well characterized by TPS-MFGDP. In the proposed method, the characteristic [M + NH₄] ⁺ adduct ions of oligosaccharides ions of oligosaccharides that are difficult for other ambient mass spectrometric methods were abundantly produced, making it possible to simultaneously identify a mixture of five or more polysaccharides. In addition, a supervised classification model which based on MS spectra, was used to classify seven typical hypoglycemic polysaccharides with excellent sensitivity, specificity and accuracy, indicating the good classification performance of the RF model constructed. Thus, the proposed mass spectroscopic method provides a cost effective, accurate and high throughput tool for identification and classification of polysaccharides, which is beneficial for studying the biological activity of polysaccharides.

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.