Pressure Photoionization Mass Spectrometry Research Articles

Direct mass spectrometry analysis of exhaled human breath in real-time.

The molecular composition of exhaled human breath can reflect various physiological and pathological conditions. Considerable progress has been achieved over the past decade in real-time analysis of exhaled human breath using direct mass spectrometry methods, including selected ion flow tube mass spectrometry, proton transfer reaction mass spectrometry, extractive electrospray ionization mass spectrometry, secondary electrospray ionization mass spectrometry, acetone-assisted negative photoionization mass spectrometry, atmospheric pressure photoionization mass spectrometry, and low-pressure photoionization mass spectrometry. Here, recent developments in direct mass spectrometry analysis of exhaled human breath are reviewed with regard to analytical performance (chemical sensitivity, selectivity, quantitative capabilities) and applications of the developed methods in disease diagnosis, targeted molecular detection, and real-time metabolic monitoring.

Positive Effect of Acetylation on Proteomic Analysis Based on Liquid Chromatography with Atmospheric Pressure Chemical Ionization and Photoionization Mass Spectrometry.

A typical bottom-up proteomic workflow comprises sample digestion with trypsin, separation of the hydrolysate using reversed-phase HPLC, and detection of peptides via electrospray ionization (ESI) tandem mass spectrometry. Despite the advantages and wide usage of protein identification and quantification, the procedure has limitations. Some domains or parts of the proteins may remain inadequately described due to inefficient detection of certain peptides. This study presents an alternative approach based on sample acetylation and mass spectrometry with atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI). These ionizations allowed for improved detection of acetylated peptides obtained via chymotrypsin or glutamyl peptidase I (Glu-C) digestion. APCI and APPI spectra of acetylated peptides often provided sequence information already at the full scan level, while fragmentation spectra of protonated molecules and sodium adducts were easy to interpret. As demonstrated for bovine serum albumin, acetylation improved proteomic analysis. Compared to ESI, gas-phase ionizations APCI and APPI made it possible to detect more peptides and provide better sequence coverages in most cases. Importantly, APCI and APPI detected many peptides which passed unnoticed in the ESI source. Therefore, analytical methods based on chymotrypsin or Glu-C digestion, acetylation, and APPI or APCI provide data complementary to classical bottom-up proteomics.

Two Rings Around One Ball: Stability and Charge Localization of [1 : 1] and [2 : 1] Complex Ions of [10]CPP and C60/70 [ *

We investigate the gas-phase chemistry of noncovalent complexes of [10]cycloparaphenylene ([10]CPP) with C60 and C70 by means of atmospheric pressure photoionization and electrospray ionization mass spectrometry. The literature-known [1 : 1] complexes, namely [10]CPP⊃C60 and [10]CPP⊃C70 , are observed as radical cations and anions. Their stability and charge distribution are studied using energy-resolved collision-induced dissociation (ER-CID). These measurements reveal that complexes with a C70 core exhibit a greater stability and, on the other hand, that the radical cations are more stable than the respective radical anions. Regarding the charge distribution, in anionic complexes charges are exclusively located on C60 or C70 , while the charges reside on [10]CPP in the case of cationic complexes. [2 : 1] complexes of the ([10]CPP2 ⊃C60/70 )+ ⋅/- ⋅ type are observed for the first time as isolated solitary gas-phase species. Here, C60 -based [2 : 1] complexes are less stable than the respective C70 analogues. By virtue of the high stability of cationic [1 : 1] complexes, [2 : 1] complexes show a strongly reduced stability of the radical cations. DFT analyses of the minimum geometries as well as molecular dynamics calculations support the experimental data. Furthermore, our novel gas-phase [2 : 1] complexes are also found in 1,2-dichlorobenzene. Insights into the thermodynamic parameters of the binding process as well as the species distribution are derived from isothermal titration calorimetry (ITC) measurements.

Solvent and Flow Rate Effects on the Observed Compositional Profiles and the Relative Intensities of Radical and Protonated Species in Atmospheric Pressure Photoionization Mass Spectrometry.

Sample preparation and instrument parameters have regularly been demonstrated to impact upon the observed results in atmospheric pressure photoionization, mass spectrometry (MS), and analytical techniques in general but may be overlooked when such methods are applied to the characterization of real-world samples. An initial investigation into different solvent systems demonstrated that the inclusion of ethyl acetate inverted the ratio of relative intensities of radical and protonated species (R/P). Design of experiments was performed and indicated that the injection flow rate is also a significant factor. The impact of the solvent system and flow rate on signal intensity, the observed compositional profile, and R/P of selected molecular groups is demonstrated further. An inversion of R/P is observed at higher flow rates in solvent systems commonly used in petroleomics studies, effecting a loss of molecular speciation. The findings presented reiterate the critical importance in considering experimental parameters when interpreting the results of analytical procedures.

Paper spray-atmospheric pressure photoionization-high resolution mass spectrometry for the direct analysis of neutral fluorinated compounds in waterproof impregnation sprays

In this work, paper spray (PS) is combined with atmospheric pressure photoionization-mass spectrometry (PS-APPI-MS) for the determination of non-polar and low polar compounds, such as the neutral per- and polyfluorinated alkyl substances (PFAS). The proposed PS-APPI-MS method has been developed for the analysis of fluorotelomer alcohols (FTOHs), fluoroctanesulfonamides (FOSAs) and fluorooctane sulfonamido-ethanols (FOSEs), using both negative ion mode and high-resolution mass spectrometry (HRMS). The most critical working parameters (i.e., UV-krypton lamp position, sample drying time, spray dopant solvent and spray voltage) have been evaluated to study both the ionization behaviour and ionization efficiency. The best results were achieved using dopant-assisted PS-APPI-HRMS with toluene as dopant solvent. The most intense ions observed in the mass spectra, [M‒H]‒ for FOSAs and [M+O2]‒• for FTOHs and FOSEs, were selected and proposed for fast screening and quantitative analysis of target compounds in waterproof impregnation sprays samples using internal standard calibration method and being able to detect down to μg L−1 levels. The satisfactory values of the method quality parameters (detection capability, repeatability, trueness and linearity) demonstrated the good performance of the PS-APPI-HRMS method and allowed the identification and quantitation of some FTOHs (6:2 FTOH, 7-Me-6:2 FTOH, 8:2 FTOH, 10:2 FTOH) and N-MeFOSE at mg L−1 in some of the waterproof impregnation spray products analyzed. This low-cost PS-APPI-HRMS method allows a fast screening, with minimum sample preparation, of non-polar and low polar compounds simultaneously, which can significantly improve the throughput on routine laboratories.

Quantitative analysis of Phthalate Esters by in-situ thermal desorption atmospheric pressure photoionization mass spectrometry using a dopant as the internal standard

Phthalate Esters (PAEs) are a group of chemicals widely used in plastic products, and they are also known as endocrine disruptors that can adversely affect the hormonal balance in humans. Since many food-contacting items, such as lunch boxes, fresh keeping film, disposable cups, are made of plastic, the PAEs can easily enter the human body through the polluted foods or drinks. Traditional analytical techniques involve laborious sample pretreatment and low-throughput analysis, so it is necessary to develop techniques that can rapidly and quantitatively detect these compounds. In this article, a miniaturized ion trap mass spectrometer (ITMS) was established firstly, then, an in-situ thermal desorption atmospheric pressure photoionization (in-situ TD-APPI) was designed, and the dopant was explored using for improving the sensitivity and as internal standard (IS) simultaneously in the analytical process. The in-situ TD-APPI presents good performance: (1) More than 20 times improvement in sensitivity compared with Nano-ESI for PAEs; (2) 12 kinds of phthalates were quantified with using acetone as the IS, and the LODs and LOQs ranges were found to be 0.02–1 μg/mL and 0.02–100 μg/mL, respectively. The technique was also applied to the quantification of mixed solutions, and the results were validated by LC/MS. Finally, six categories of food-contacting items containing PAEs were analyzed with superficial content (ng/cm2) ranging from 0 to 6.20 ng/cm2. These results demonstrate the potential of rapid quantification of analysis of PAEs in practical plastic food-contacting items by in-situ TD-APPI.

Mass Spectrometry Imaging of Arabidopsis thaliana Leaves at the Single-Cell Level by Infrared Laser Ablation Atmospheric Pressure Photoionization (LAAPPI).

In this study, we show that infrared laser ablation atmospheric pressure photoionization mass spectrometry (LAAPPI-MS) imaging with 70 μm lateral resolution allows for the analysis of Arabidopsis thaliana (A. thaliana) leaf substructures ranging from single-cell trichomes and the interveinal leaf lamina to primary, secondary, and tertiary veins. The method also showed its potential for depth profiling analysis for the first time by mapping analytes at the different depths of the leaf and spatially resolving the topmost trichomes and cuticular wax layer from the underlying tissues. Negative ion LAAPPI-MS detected many different flavonol glycosides, fatty acids, fatty acid esters, galactolipids, and glycosphingolipids, whose distributions varied significantly between the different substructures of A. thaliana leaves. The results show that LAAPPI-MS provides a highly promising new tool to study the role of metabolites in plants.

Lipid composition of the stratum corneum in different regions of the body of Kuhl's pipistrelle from the Negev Desert, Israel

The most superficial epidermal layer in endotherms is the stratum corneum (SC), which is composed of dead corneocytes embedded in a lipid matrix with free fatty acids, cholesterol, ceramides, and cerebrosides; the lipid composition of the SC determines its permeability to water vapor. Lipids that are more polar, have longer hydrocarbon chains, and are less bulky are often packed in more ordered phase states to slow cutaneous evaporative water loss (CEWL); these lipids also resist transitions to more disordered phases at high ambient temperatures (Ta). In bats, wing and tail membranes (wing patagia and tail uropatagium, respectively) allow powered flight, but increase surface area, and hence CEWL, with implications for survival in arid environments. We captured Pipistrellus kuhlii from an arid habitat and measured the lipid composition of the SC of the plagiopatagium in the wing, the uropatagium, and the non-membranous region (NMR) of the body using thin layer chromatography and reversed phase high performance liquid chromatography coupled with atmospheric pressure photoionization mass spectrometry. The patagia contained more cholesterol and shorter-chained ceramides, and fewer cerebrosides than the NMR, indicating that the lipid phase transition temperature in the patagia is lower than in the NMR. Thus, at moderate Ta the lipids in the SC in all body regions will remain in an ordered phase state, allowing water conservation; but as Ta increases, the lipids in the SC of the patagia will more easily transition into a disordered phase, resulting in increased CEWL from the patagia facilitating efficient heat dissipation in hot environments.

Sub-100 μm Spatial Resolution Ambient Mass Spectrometry Imaging of Rodent Brain with Laser Ablation Atmospheric Pressure Photoionization (LAAPPI) and Laser Ablation Electrospray Ionization (LAESI).

In this study, we applied a new IR laser-beam-focusing technique to enable sub-100 μm spatial resolution in laser ablation atmospheric pressure photoionization (LAAPPI) and laser ablation electrospray ionization (LAESI) mass spectrometry imaging (MSI). After optimization of operational parameters, both LAAPPI- and LAESI-MSI with a spatial resolution of 70 μm produced high-quality MS images, which allowed accurate localization of metabolites and lipids in the mouse and rat brain. Negative and positive ion LAAPPI- and LAESI-MS detected many of the same metabolites and lipids in the brain. Many compounds were also detected either by LAAPPI- or LAESI-MS, indicating that LAAPPI and LAESI are more complementary than alternative methods.

Rapid and highly sensitive measurement of trimethylamine in seawater using dynamic purge-release and dopant-assisted atmospheric pressure photoionization mass spectrometry

Trimethylamine (TMA) is ubiquitous in the marine systems and may affect atmospheric chemistry as a precursor and strong stabilizer of atmospheric secondary aerosol, influencing cloud formation. Rapid and accurate measurement of the concentration of TMA in seawater is challenging due to their polarity, aqueous solubility, volatility and existence at low concentrations in marine environments. In this study, a dopant-assisted atmospheric pressure photoionization time-of-flight mass spectrometry (DA-APPI-TOFMS) coupled with a dynamic purge-release method was developed for rapid and sensitive analysis of TMA in seawater. A novel three-zones ionization source has been developed for improving the ionization efficiency of analyte molecules and minimizing the influence of high-humidity of the sample gas, which allowed direct analysis of high-humidity (RH> 90%) gas samples from microbubble purging process by the mass spectrometer. At atmospheric pressure, the three-zones ionization source allows the use of high-speed purge gas to quickly purge all organic amines dissolved in the water into the gas phase, ensuring quantitative accuracy. The limit of quantification (LOQ) for TMA down to 0.1 μg L−1 was obtained in less than 2 min by consuming only 2 mL seawater sample. This method was applied for the determination of the concentrations of TMA in the coastal seawater to validate its practicability and reliability for analysis of trace amines in marine environments.

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.

Analysis of linoleoyl and oleoyl macrogolglycerides by high performance liquid chromatography coupled to the atmospheric pressure photoionization mass spectrometry

Linoleoyl macrogolglyceride (LM) and oleoyl macrogolglyceride (OM) are pharmaceutical ingredients, obtained from corn and apricot kernel oils respectively. This study aims to know the detailed chemical composition of LM and OM, in order to understand their roles in pharmaceutical formulations. These two products were analyzed by non-aqueous reversed phase high-performance liquid chromatography (NARP-HPLC), using Vintage Series KR C18 column (250 × 4.6 mm, 5 µm) and non-aqueous acetonitrile/acetone mixture as mobile phase. The ionization source used was atmospheric pressure photoionization (APPI) and the analyzer was LTQ-Orbitrap® (hybrid analyzer: double linear ion trap coupled to a Fourier transform orbital trap). LM and OM consist of complex mixtures, constituted of mono-(MG), di-(DG) and triglycerides (TG) and mono-(MPEGE) and di PEG-6 esters (DPEGE) of linoleic acid (18:2) for LM and of oleic acid (18:1) for OM. NARP-HPLC-APPI method allowed the separation and the identification of the glyceride classes (MGs, DGs and TGs) and the PEG esters of different chain lengths (PEG-chain lengths of fatty acid moieties and number of units of ethylene oxide), at the same time and in one single run, for both products LM and OM. The comparative study between LM and OM showed that, a higher presence of linoleic esters for LM, and a higher presence of oleic esters for OM.

In Situ Atmospheric Pressure Photoionization Mass Spectrometric Monitoring of Initial Pyrolysis Products of Biomass in Real Time.

Knowledge on the initial and intermediate pyrolysis products of biomass is essential for the mechanistic investigation of biomass pyrolysis and further optimization of upgrading processes. The conventional method can only detect the final products, which do not resemble the initial or intermediate pyrolysis products. Here, we introduce a direct orifice sampling combined with atmospheric pressure photoionization mass spectrometry (APPI-MS) for in situ online analysis of the evolved volatile initial products from the pyrolysis of biomass. Pyrolysis experiments of both dimeric model compound (guaiacylglycerol-β-guaiacyl ether, GGGE) and poplar wood were carried out to validate the generality of the method. Generally, secondary reactions can be reduced by shortening the distance between the sample and sampling orifice. Large molecular-weight initial products up to trimers were detected during the pyrolysis of poplar wood, and no initial products larger than trimers were detected. It is inferred that in situ APPI immediately after sample extraction ensures efficient and effective product detection. Furthermore, the present work offers a promising feasible method for online tracing of reaction intermediates not only in pyrolysis but also in various reactive processes (e.g., catalytic reaction, oxidation) under operando conditions.

Characterization of polycyclic aromatic hydrocarbons and their phenanthroperylene quinone precursors in fossil crinoids using liquid chromatography–atmospheric pressure photoionization mass spectrometry

The distribution and origin of diagenetic products of polycyclic quinone pigments in fossil crinoids was investigated using high-performance liquid chromatography–diode array detection–atmospheric pressure photoionization mass spectrometry (HPLC–DAD–APPI-MS). A number of characteristic higher-molecular-weight polycyclic aromatic hydrocarbons (PAHs) were identified in toluene extracts of diverse crinoid samples, with 1,2,3,4,5,6-hexahydrophenanthro[1,10,9,8-opqra]perylene as the main compound. Moreover, phenanthro[1,10,9,8-opqra]perylene-7,14-dione (PPQ) and further derivatives were detected for the first time in the fossil record, representing intermediates between hydroxylated phenanthroperylene quinone pigments such as fringelite F and phenanthroperylene PAHs. The widespread presence of PPQ, its derivatives and related PAHs in fossil crinoids which contain phenanthroperylene quinone pigments confirms the diagenetic formation of specific PAHs by reductive degradation of quinone pigments.

Thermogravimetry coupled to an atmospheric pressure photo ionization quadrupole mass spectrometry for the product control of pharmaceutical formulations and the analysis of plasticizers in polymers

The development of a thermogravimetry coupled to an atmospheric pressure photoionization mass spectrometry (TG-APPI-MS) with a high temperature and flexible transfer line is presented. A method was developed to analyze plasticizers in solution which consist of a solvent evaporation step and subsequent evaporation of the analyte. These solutions of dibutyl phthalate (DBP) in hexane were used to investigate the repeatability (RSD: 3.6%) and linearity (R2: 0.9995) of the new developed system. With the new device the detection of different phthalates in a standardized PVC (polyvinyl chloride) polymer is shown. On the example of ASA, the degradation of a pharmaceutical drug is investigated. The dimerization and the possible trimerization of ASA during the thermal degradation is shown. Ten tablets of different ASA manufacturers were analyzed with the new developed analysis platform. The active substance was found in every tablet. Differences in mass spectral data as well as the studying of the pack insert were used to assign the tablets to companies and their subsidiaries. A unique formulation of ASA was found to have a different mass pattern when analyzed with TG-APPI-qMS. The developed device is a promising tool for the product control and the identification of falsified drugs.

Atmospheric Pressure Photoionization Mass Spectrometry: New Capabilities for the Determination of the Numbers of Components in Complex Mixtures and Their Identification

The atmospheric pressure photoionization and photochemical ionization mass spectrometry (APPI/APPCI−MS) makes it possible to compare the number of peaks in a mass spectrum with the number of components in the test mixture because of the measurements of the mass spectra of individual compounds, which mainly consist of the peaks of a molecular ion (M+) or a protonated molecule (MH+). The capabilities of gas chromatography–electron ionization (EI) and atmospheric pressure ionization mass spectrometry for the identification of trace components of complex mixtures are considered. The advantages of APPI/APPCI−MS, which makes it possible to increase the reliability of the detection of components in the complex mixtures of organic compounds, over EI mass spectrometry are shown. The work was performed at the Department of Analytical Chemistry, Faculty of Chemistry, Moscow State University.

Direct and rapid analysis of trace levels steroids in water by thermal desorption atmospheric pressure photoionization mass spectrometry

A novel TD-APPI technique for steroid analysis at trace levels from a 10 μL water sample without derivatization and chromatographic separation.

Molecular Characterization of Ketones in a Petroleum Source Rock

A comprehensive investigation of oil composition is important for the petroleum industry as well as the understanding of natural science. Ketones commonly exist in petroleum; however, as a result of the low concentrations and limitations inherent in the analytical technique, the molecular composition of these compounds is rarely studied. In this study, ketones in a source rock were characterized by gas chromatography–mass spectrometry, Fourier transform ion cyclotron resonance mass spectrometry, and Orbitrap mass spectrometry. Ketones were derivatized with the Girard T reagent under weakly acidic conditions to enhance their detectability by electrospray ionization mass spectrometry (ESI MS) analysis. Atmospheric pressure photoionization mass spectrometry (APPI MS) was also used for the molecular characterization of ketones without chemical derivatization. The characterization techniques were complementary to each other, and the results were consistent in general. The chemical derivatization followed by po...

Carotenoids: Experimental Ionization Energies and Capacity at Inhibiting Lipid Peroxidation in a Chemical Model of Dietary Oxidative Stress.

Carotenoids are important natural pigments and micronutrients contributing to health prevention by several mechanisms, including their electron-donating (antioxidant) activity. In this work, a large series of carotenoids, including 11 carotenes and 14 xanthophylls, have been investigated by wavelength-resolved atmospheric pressure photoionization mass spectrometry (DISCO line of SOLEIL synchrotron), thus allowing the experimental determination of their ionization energy (IE) for the first time. On the other hand, the carotenoids have been also investigated for their ability to inhibit the heme iron-induced peroxidation of linoleic acid in mildly acidic micelles, a simple but relevant chemical model of oxidative stress in the gastric compartment. Thus, the carotenoids can be easily classified from IC50 concentrations deduced from the time dependence of the lipid hydroperoxide concentration. With a selection of two carotenes and three xanthophylls a quantitative analysis is also provided to extract stoichio-kinetic parameters. The influence of the carotenoid structure (number of conjugated carbon-carbon double bonds, presence of terminal six-membered rings, hydroxyl, keto, and/or epoxy groups) on the IE, IC50, and stoichio-kinetic parameters is discussed in details. The data show that the antioxidant activity of carotenes is well correlated to their electron-donating capacity, which itself largely depends on the length of the conjugated polyene chain. By contrast, the IE of xanthophylls is poorly correlated to the polyene chain length because of the strong, and sometimes unexpected, electronic effects of the O-atoms. Although IE remains an approximate predictor of the antioxidant activity of xanthophylls, other factors (interaction with the aqueous phase, competing radical-scavenging mechanisms, the residual activity of the antioxidant's oxidation products) probably play a significant role.

Solvent composition dependent signal reduction of molecular ions generated from aromatic compounds in (+) atmospheric pressure photoionization mass spectrometry.

The ionization process is essential for successful mass spectrometric (MS) analysis because of its influence on selectivity and sensitivity. In particular, certain solvents reduce the ionization of the analyte, thereby reducing the overall sensitivity in atmospheric pressure photoionization (APPI). Since the sensitivity varies greatly depending on the solvents, a fundamental understanding of the mechanism is required. Standard solutions were analyzed using a (+)-APPI Q Exactive ion trap mass spectrometer (Thermo Scientific). Each solution was infused directly into the APPI source at a flow rate of 100μL/min and the APPI source temperature was 300°C. Other operating mass spectrometric parameters were maintained under the same conditions. Quantum mechanical calculations were carried out using the Gaussian 09 suite program. Density functional theory was used to calculate the reaction enthalpies (∆H) of the reactions between toluene and other solvents. The experimental and theoretical results showed good agreement. The abundances of analyte ions were well correlated with the calculated ∆H values. Therefore, the results strongly support the suggested signal reduction mechanism. In addition, linear correlations between the abundance of toluene and analyte molecular ions were observed, which also supports the suggested mechanism. A solvent composition dependent signal reduction mechanism was suggested and evaluated for the (+)-APPI-MS analysis of polyaromatic hydrocarbons (PAHs) generating mainly molecular ions. Overall, the evidence provided in this work suggests that reactions between solvent cluster(s) and toluene molecular ions are responsible for the observed reductions in signal.