Showing papers on "Atmospheric-pressure chemical ionization published in 2016"
TL;DR: Calculations indicate that relatively simple quantum chemical methods can predict the sensitivity of an iodide-based CIMS instrument toward most molecules, but higher level calculations were needed to treat some outlier molecules, most notably oxalic acid and methylerythritol.
Abstract: Iodide-based chemical ionization mass spectrometry (CIMS) has been used to detect and measure concentrations of several atmospherically relevant organic and inorganic compounds. The significant electronegativity of iodide and the strong acidity of hydroiodic acid makes electron transfer and proton abstraction essentially negligible, and the soft nature of the adduct formation ionization technique reduces the chances of sample fragmentation. In addition, iodide has a large negative mass defect, which, when combined with the high resolving power of a high resolution time-of-flight chemical ionization mass spectrometer (HR–ToF–CIMS), provides good selectivity. In this work, we use quantum chemical methods to calculate the binding energies, enthalpies and free energies for clusters of an iodide ion with a number of atmospherically relevant organic and inorganic compounds. Systematic configurational sampling of the free molecules and clusters was carried out at the B3LYP/6-31G* level, followed by subsequent ca...
81 citations
TL;DR: A three-step data-processing approach that enables congener group-level resolution of CP mixtures in environmental samples, and it opens up the possibility for quantification of congener groups.
Abstract: We describe and illustrate a three-step data-processing approach that enables individual congener groups of chlorinated paraffins (CPs) to be resolved in mass spectra obtained from either of two soft ionization methods: electron capture negative ionization mass spectrometry (ECNI-MS) or atmospheric pressure chemical ionization mass spectrometry (APCI-MS). In the first step, general fragmentation pathways of CPs are deduced from analysis of mass spectra of individual CP congeners. In the second step, all possible fragment ions in the general fragmentation pathways of CPs with 10 to 20 carbon atoms are enumerated and compared to mass spectra of CP mixture standards, and a deconvolution algorithm is applied to identify fragment ions that are actually observed. In the third step, isotope permutations of the observed fragment ions are calculated and used to identify isobaric overlaps, so that mass intensities of individual CP congener groups can be deconvolved from the unresolved isobaric ion signal intensitie...
68 citations
TL;DR: A new supercritical fluid chromatography-mass spectrometry (SFC-MS) method has been developed for the separation of nine vitamin D metabolites within less than eight minutes, and its potential was applied to human plasma samples from healthy individuals.
66 citations
TL;DR: Though solution basicity of a compound is the main factor initially determining the ESI response of the protonated molecular ion, other factors such as polarity and vaporability become more important under acidic solvent conditions and may nearly outweigh the importance of basicity under these conditions.
Abstract: Over the past decades, electrospray ionization for mass spectrometry (ESI-MS) has become one of the most commonly employed techniques in analytical chemistry, mainly due to its broad applicability to polar and semipolar compounds and the superior selectivity which is achieved in combination with high resolution separation techniques. However, responsiveness of an analytical method also determines its suitability for the quantitation of chemical compounds; and in electrospray ionization for mass spectrometry, it can vary significantly among different analytes with identical solution concentrations. Therefore, we investigated the ESI-response behavior of 56 nitrogen-containing compounds including aromatic amines and pyridines, two compound classes of high importance to both, synthetic organic chemistry as well as to pharmaceutical sciences. These compounds are increasingly analyzed employing ESI mass spectrometry detection due to their polar, basic character. Signal intensities of the peaks from the protonated molecular ion (MH+) were acquired under different conditions and related to compound properties such as basicity, polarity, volatility and molecular size exploring their quantitative impact on ionization efficiency. As a result, we found that though solution basicity of a compound is the main factor initially determining the ESI response of the protonated molecular ion, other factors such as polarity and vaporability become more important under acidic solvent conditions and may nearly outweigh the importance of basicity under these conditions. Moreover, we show that different molecular descriptors may become important when using different types of instruments for such investigations, a fact not detailed so far in the available literature.
64 citations
TL;DR: Developments leading to the discovery of a seemingly magic ionization process that is simple to use, fast, sensitive, robust, and can be directly applied to surface characterization using portable or high performance mass spectrometers are covered.
62 citations
TL;DR: Overall, this study evidences the intrinsic limitations and benefits of each of the three sources, and should provide the fundamental knowledge required to expand the power of crude oil analysis by high-resolution mass spectrometry.
54 citations
TL;DR: A nanoLC/EI-MS method was developed for elucidation of the free fatty acid profile in mussel samples, avoiding a previous derivatization step, required when gas chromatographic analysis is involved.
Abstract: Recently the miniaturization of liquid chromatography (LC) systems and progresses in mass spectrometry instrumentation have enabled direct introduction of the effluent coming from a nanoLC column into the high-vacuum region of an electron ionization source. In the present research, a nanoLC system was directly coupled to an electron ionization mass spectrometer (EI-MS) without any interface or modification of the ion source. The advantage with respect to atmospheric pressure ionization techniques, normally coupled with LC, is major identification power because of a more extensive and reproducible fragmentation pattern, without any matrix effect or mobile-phase interference. In particular, a nanoLC/EI-MS method was developed for elucidation of the free fatty acid profile in mussel samples, avoiding a previous derivatization step, required when gas chromatographic analysis is involved. A total of 20 fatty acids were reliably identified through the comparison with commercial libraries. A quantitative determination was also carried out by using the response factors approach along with the internal standard method, allowing for quantification of 14 fatty acids. Among them, palmitic acid resulted the most abundant, followed by ω6 arachidonic acid. The quantitative data were compared with those obtained by a well-established technique, such as gas chromatography with flame ionization detection (GC-FID). Both nanoLC/EI-MS and GC-FID methods were validated and similar results were obtained in terms of limit of detection and quantification, resulting in the picomole range, and sensitivity as well was not significantly different, as demonstrated by comparing the slope values of the calibration curves (p < 0.05, from a t-test).
54 citations
TL;DR: In this article, a rapid and sensitive ultra-high performance supercritical fluid chromatography-mass spectrometry (UHPSFC-MS) method has been developed and partially validated for the separation of carotenoids within less than 6min.
Abstract: In this study, a rapid and sensitive ultra-high performance supercritical fluid chromatography-mass spectrometry (UHPSFC-MS) method has been developed and partially validated for the separation of carotenoids within less than 6 min. Six columns of orthogonal selectivity were examined, and the best separation was obtained by using a 1-aminoanthracene (1-AA) column. The length of polyene chain as well as the number of hydroxyl groups in the structure of the studied carotenoids determines their differences in the physiochemical properties and thus the separation that is achieved on this column. All of the investigated carotenoids were baseline separated with resolution values greater than 1.5. The effects of gradient program, back pressure, and column temperature were studied with respect to chromatographic properties such as retention and selectivity. Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) were compared in both positive and negative mode, using both direct infusion and hyphenated with UHPSFC. The ESI in positive mode provided the highest response. The coefficient of determination (R
2) for all calibration curves were greater than 0.998. Limit of detection (LOD) was in the range of 2.6 and 25.2 ng/mL for α-carotene and astaxanthin, respectively, whereas limit of quantification (LOQ) was in the range of 7.8 and 58.0 ng/mL for α-carotene and astaxanthin, respectively. Repeatability and intermediate precision of the developed UHPSFC-MS method were determined and found to be RSD < 3 % and RSD < 6 %, respectively. The method was applied in order to determine carotenoids in supercritical fluid extracts of microalgae and rosehip.
51 citations
TL;DR: PetroOrg as mentioned in this paper is a software package used to compare IM-MS data sets recorded with atmospheric solid analysis probe (ASAP) and three other atmospheric pressure ionization sources.
Abstract: Because of its high molecular complexity, ultra high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is used to characterize heavy petroleum distillates. However, high peak capacity can also be obtained with ion mobility-mass spectrometry (IM-MS). In this case, the additional separation dimension allows for the compensation of the lower resolving power of the time-of-flight mass analyzer. The processing and elemental composition assignments from such bidimensional IM-MS data cannot be achieved with conventional software packages. PetroOrg, a new software package, was used to compare IM-MS data sets recorded with atmospheric solid analysis probe (ASAP) and three other atmospheric pressure ionization sources. The choice of the ionization source is indeed very critical as it defines the type of compounds that can be detected from mixtures. Electrospray ionization (ESI) is very specific to polar compounds and yields relatively simple data sets that can be readily attributed t...
50 citations
TL;DR: A new high-pressure photon ionization (HPPI) ion source based on a vacuum ultraviolet (VUV) Kr lamp was developed for time-of-flight mass spectrometry (TOFMS) and successfully identified and quantified several frequently reported VOCs in the breath of healthy volunteers.
Abstract: Photon ionization mass spectrometry (PI-MS) is a widely used technique for the online detection of trace substances in complex matrices. In this work, a new high-pressure photon ionization (HPPI) ion source based on a vacuum ultraviolet (VUV) Kr lamp was developed for time-of-flight mass spectrometry (TOFMS). The detection sensitivity was improved by elevating the ion source pressure to about 700 Pa. A radio frequency (RF)-only quadrupole was employed as the ion guide system following the HPPI source to achieve high ion transmission efficiency. In-source collision induced dissociation (CID) was conducted for accurate chemical identification by varying the voltage between the ion source and the ion guide. The high humidity of the breath air can promote the detection of some compounds with higher ionization potentials (IPs) that could not be well detected by single photon ionization (SPI) at low pressure. Under 100% relative humidity (37 °C), the limits of detection down to 0.015 ppbv (parts per billion by volume) for aliphatic and aromatic hydrocarbons were obtained. This HPPI-TOFMS system was preliminarily applied for online investigations of the exhaled breath from both healthy nonsmoker and smoker subjects, demonstrating its analytical capacity for complicated gases analysis. Subsequently, several frequently reported VOCs in the breath of healthy volunteers, i.e., acetone, isoprene, 2-butanone, ethanol, acetic acid, and isopropanol, were successfully identified and quantified.
48 citations
TL;DR: Due to increased sensitivity and user friendly operation under atmospheric pressure, GC/APCI/MS/MS is a powerful alternative technique that can easily meet the specification of GC/HRMS.
TL;DR: A novel solid-phase extraction procedure was developed and demonstrated that it allowed for good recoveries of the three families of analytes without artifactual oxidation of cholesterol and found that 16 weeks of high-fat diet strongly impacted the hepatic levels of several oxysterols, ceramides, and endocannabinoids.
Abstract: Oxysterols, ceramides, and endocannabinoids are three families of bioactive lipids suggested to be involved in obesity and metabolic syndrome. To facilitate the quantification of these potentially interconnected lipids, we have developed and validated a liquid chromatography coupled to mass spectrometry method allowing for their simultaneous quantification from tissues. Sample purification is of great importance when quantifying oxysterols due to the potential artifactual conversion of cholesterol into oxysterols. Therefore, we developed a novel solid-phase extraction procedure and demonstrated that it allowed for good recoveries of the three families of analytes without artifactual oxidation of cholesterol. The oxysterols, ceramides, and endocannabinoids and their respective internal standards were chromatographically separated by HPLC and ionized using the atmospheric pressure chemical ionization (APCI) source of an LTQ-orbitrap mass spectrometer. The repeatability and bias were within the acceptance limits for all 23 lipids of interest. The sensitivity (limit of detection (LOD) and limit of quantification (LOQ)) and specificity of the method allowed us to quantify all the analytes in the liver and adipose tissue of control and high-fat diet-fed C57BL/6 mice. We found that 16 weeks of high-fat diet strongly impacted the hepatic levels of several oxysterols, ceramides, and endocannabinoids. A partial least-squares discriminant analysis (PLS-DA) based on the variations of the hepatic levels of these 23 bioactive lipids allowed differentiating the lean mice from the obese mice.
TL;DR: A reliable, rapid and sensitive method based on laser diode thermal desorption/atmospheric pressure chemical ionization (LDTD/APCI) coupled with tandem mass spectrometry (MS/MS) has been developed for the quantification of DCF in wastewater and wastewater sludge.
TL;DR: Direct infusion atmospheric pressure chemical ionization mass spectrometry (APCI) shows potential as an alternative of FI-MS in lubricant base oil analysis and the reproducibility of APCI-MS method was found to be substantially better than forFI-MS.
Abstract: Direct infusion atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was compared to field ionization mass spectrometry (FI-MS) for the determination of hydrocarbon class distributions in lubricant base oils. When positive ion mode APCI with oxygen as the ion source gas was employed to ionize saturated hydrocarbon model compounds (M) in hexane, only stable [M – H]+ ions were produced. Ion–molecule reaction studies performed in a linear quadrupole ion trap suggested that fragment ions of ionized hexane can ionize saturated hydrocarbons via hydride abstraction with minimal fragmentation. Hence, APCI-MS shows potential as an alternative of FI-MS in lubricant base oil analysis. Indeed, the APCI-MS method gave similar average molecular weights and hydrocarbon class distributions as FI-MS for three lubricant base oils. However, the reproducibility of APCI-MS method was found to be substantially better than for FI-MS. The paraffinic content determined using the APCI-MS and FI-MS methods for the b...
TL;DR: In this paper, a comprehensive characterization of cluster control and transmission through the Tofwerk atmospheric pressure interface installed on various chemical ionization time-of-flight mass spectrometers using authentic standards is presented.
Abstract: . We present a comprehensive characterization of cluster control and transmission through the Tofwerk atmospheric pressure interface installed on various chemical ionization time-of-flight mass spectrometers using authentic standards. This characterization of the atmospheric pressure interface allows for a detailed investigation of the acetate chemical ionization mechanisms and the impact of controlling these mechanisms on sensitivity, selectivity, and mass spectral ambiguity with the aim of non-targeted analysis. Chemical ionization with acetate reagent ions is controlled by a distribution of reagent ion-neutral clusters that vary with relative humidity and the concentration of the acetic anhydride precursor. Deprotonated carboxylic acids are primarily detected only if sufficient declustering is employed inside the atmospheric pressure interface. The configuration of a high-resolution time-of-flight chemical ionization mass spectrometer (HR-TOF-CIMS) using an acetate chemical ionization source for non-targeted analysis is discussed. Recent approaches and studies characterizing acetate chemical ionization as it applies to the HR-TOF-CIMS are evaluated in light of the work presented herein.
TL;DR: The major ion formation mechanism of CFI-MS was suggested to involve desorption in a steam-distillation-like process, and then, ionization occurred mainly via corona discharge under high voltage.
Abstract: A carbon fiber ionization (CFI) technique was developed for the mass spectrometric analysis of various organic compounds with different polarities. The design of the CFI technique was based on the good compatibility and dispersion of samples and solutions in different solvents on carbon fiber. As a fast, convenient, and versatile ionization method, CFI-MS is especially efficient for analyzing many low/nonpolar organic compounds, such as polycyclic aromatic hydrocarbons, long-chain aliphatic aldehydes, sensitive steroids, terpenoids, and organometallic compounds. Some of these compounds may not be well-analyzed by electrospray ionization or electron ionization mass spectrometry. On the basis of our experimental results, the major ion formation mechanism of CFI-MS was suggested to involve desorption in a steam-distillation-like process, and then, ionization occurred mainly via corona discharge under high voltage. CFI-MS could not only work alone but also be coupled with separation techniques. It works well ...
TL;DR: In this paper, an initial parametric evaluation is performed using caffeine as the test molecule, with a preliminary limit of detection of 5.9 × 10−9 M (43 pg) for 20 μL injections.
Abstract: This laboratory has demonstrated the analytical versatility of the liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source. Demonstrations have included elemental analysis of solutions and laser ablation (LA)-produced aerosols, ambient desorption of small organic molecules on substrates, and direct speciation of organometallic complexes in solution. Here we present initial efforts in mapping the operation space of the device as it applies to obtaining molecular mass spectra from diverse organic molecules. An initial parametric evaluation is performed using caffeine as the test molecule, with a preliminary limit of detection of 5.9 × 10−9 M (43 pg) for 20 μL injections. Conditions optimum for that molecule are applied in assessing the qualitative nature of spectra from caffeine, sinapinic acid, daidzin (a flavonoid), a FITC-labeled lipid tethered ligand, the mass marker Ultramark 1621, and the heme-protein myoglobin. The product spectra for the small molecules are very much like what would be obtained from electrospray and atmospheric pressure chemical ionization sources, predominately the production of the protonated pseudomolecular ion of the form (M + H)+. The mid-range molecules show ion signatures of the thermally stable fragments. Finally, the macromolecules yield mass spectra that are very much like those from electrospray, producing a range of protonated charged states. While much optimization and understanding are needed to best apply the source to such solutes, the fact that the same ion source can be used across the spectrum from elemental/isotopic analysis to perhaps proteomics is totally unique and is worthy of continued development.
TL;DR: Photoionization using acetone as a dopant is distinguished by a significantly higher intensity of signals and the lowest sensitivity to contaminants present in the lignin preparation, and can be considered as preferred for studying the dioxane lign in preparations of woody plants.
Abstract: RATIONALE Mass spectrometry with atmospheric pressure ionization is the most promising method for studying the structure of natural lignin, which is the second most abundant biopolymer in nature. The goal of this study is to compare the efficiency and characteristics of different types of ionization techniques (ESI, APCI, and APPI) in the negative ion mode by the example of softwood lignin. METHODS As the subjects of the study, we selected a preparation of spruce dioxane lignin and several phenols, simulating the basic structural fragments of the lignin macromolecule. High-resolution mass spectra were recorded using an Orbitrap mass spectrometer. Acetone was used as a solvent for samples and a dopant in photoionization mode. The ionization conditions were optimized to achieve the maximum intensity of the mass spectra. RESULTS The formation of deprotonated lignin molecules is characteristic of all the studied types of ionization; partial fragmentation of the biopolymer occurs in all ionization modes. ESI in the presence of ammonia yields low-intensity signals, leads to a significant decrease in ionization efficiency with increasing molecular weight of lignin oligomers, gives high-intensity impurity peaks in the mass spectra, and demonstrates selectivity for more polar structures. The ionization efficiency increases sharply in the order of ESI < APCI < APPI. The two latter methods are characterized by similar mechanisms of ionization; they ensure detection of approximately 1900 spruce lignin oligomers in the range of molecular weights up to 1.8 kDa. The determination of the elemental composition of oligolignols enabled the four main groups of compounds to be distinguished. CONCLUSIONS Photoionization using acetone as a dopant is distinguished by a significantly higher intensity of signals and the lowest sensitivity to contaminants present in the lignin preparation. This ionization method can be considered as preferred for studying the dioxane lignin preparations of woody plants. Copyright © 2016 John Wiley & Sons, Ltd.
TL;DR: The results presented show that the proposed APCI-HRqTOFMS method was comparable and in many cases an improvement on the existing EI-HRMS method.
Abstract: A method to determine halogenated flame retardants was developed that utilizes gas chromatography with atmospheric chemical ionization (APCI) high-resolution quadrupole time-of-flight mass spectrometry (HRqTOFMS). The new GC-APCI-HRqTOFMS method was used to determine the presence of 65 halogenated flame retardants (HFRs) in the United Sates National Institute of Standards and Technology (NIST) organic contaminants in house dust standard reference material (SRM). The accuracy of the measurements was compared to the certified NIST value for polybrominated diphenyl ethers (PBDEs) and had an average accuracy for the 14 certified PBDEs of 109% with subpicogram detection limits (on column) from a single 1 μL injection with a run time of 18 min. SRM2585 extracts were also analyzed by GC electron ionization (EI) high-resolution mass spectrometry (HRMS), and there was an excellent correlation between the two data sets (R2 value of 0.996). The presence of 25 additional HFRs were also screened in the dust standard, ...
TL;DR: This work investigates the underlying ionization mechanisms and reaction pathways for the formation of protonated analyte and proposes a radical-mediated ionization pathway, which proceeds by direct reaction of the ionized plasma gas with the analyte.
TL;DR: In this paper, a numerical method that merges the analytical solution that describes the angle of aperture and the current of an ideal electrospray, with a finite element method was developed to enable the evaluation of complex geometries.
Abstract: The process by which ambient vapors are ionized upon interaction with electrosprays is not fully understood, compromising its optimization and widespread use. In this work we evaluated the different scales associated with the processes involved in secondary electrospray ionization (SESI), and developed a new numerical method that merges the analytical solution that describes the angle of aperture and the current of an ideal electrospray, with a finite element method that enables the evaluation of complex geometries. The numerical method showed that, despite the low ionization efficiency (i.e. ion concentration/neutral vapor concentration ∼10−4), depletion of neutral vapors plays an important role. We used this method to optimize and design a low flow SESI source, which was coupled with a commercial high resolution/high mass accuracy mass spectrometer. The system was designed to be interfaced with virtually any pre-existing atmospheric pressure ionization mass spectrometer. The experimental validation for the detection of ambient vapors confirmed qualitatively the numerical predictions in terms of ionization efficiency as a function of sample flow rate. As a result of the optimization, this prototype showed a 5-fold sensitivity increase against standard SESI. This novel add-on is meant to upgrade mass spectrometers to analyze trace gases in real time by SESI technique.
TL;DR: GC-(APCI)MS/MS has been proved as a suitable alternative to the traditionally accepted confirmation method based on the use of high resolution mass spectrometry and other triple quadrupole tandem mass spectromaetry techniques operating with electron ionization.
TL;DR: The analogous ether cleavages of PBDDs and PXDDs were studied using a gas chromatograph-quadrupole time-of-flight (GC-QTOF) mass spectrometer coupled using APCI, indicating comparable detection limits for the radical cations and negative pseudomolecular ions.
Abstract: Brominated and mixed halogenated dibenzo-p-dioxins (PBDDs and PXDDs) may well be as toxic as 2,3,7,8-tetrachloro-dibenzo-p-dioxin (2378-TCDD), a compound reputed as one of the most toxic chemicals known to exist. However, studies on the occurrence of PXDDs have been hampered by a lack of authentic standards as well as separation techniques capable of resolving the enormous number of potential isomers. Electron ionization (EI) mass spectrometry based methods are of limited value due to the lack of isomer specific fragmentation. Negative ion atmospheric pressure chemical ionization (APCI–) of 2378-TCDD was described in this journal over 30 years ago. Under these conditions, the reaction between O2–• and 2378-TCDD results in structure diagnostic cleavages of the C–O bonds, which can distinguish TCDD isomers on the basis of Cl distribution between the two aromatic rings. In the present study, the analogous ether cleavages of PBDDs and PXDDs were studied using a gas chromatograph-quadrupole time-of-flight (GC-...
TL;DR: The results suggest that the electrolyte degradation is correlated with the formation of a solid electrolyte interphase, which is an important factor in the performance of LIBs.
Abstract: Rationale Improvement of lithium ion batteries (LIBs) in terms of performance and robustness requires good understanding of the reaction processes. The analysis of the individual degradation products in LIB electrolytes and on the surface of the electrodes provides vital information in this regard. In this study, mass spectrometric analytical methods were utilized for the identification of the individual degradation products. Methods The degradation products in the electrolytes recovered from cycle-tested cells were separated by liquid chromatography (LC) and their mass spectrometric analysis was conducted by electrospray ionization mass spectrometry (ESI-MS). For identification of degradation products on the surface of electrodes, atmospheric solid analysis probe (ASAP)-MS analysis was conducted by time-of-flight mass spectrometry with an ASAP probe and an atmospheric pressure chemical ionization source. Results The degradation products in the electrolytes, namely carbonate oligomers and organophosphates, were identified simultaneously by LC/ESI-MS. Their formation mechanisms were estimated, which explain their different compositions at different temperatures. One degradation product was found on the anode surface by ASAP-MS, and its formation mechanism was explained similarly to those in the electrolyte. Conclusions The results suggest that the electrolyte degradation is correlated with the formation of a solid electrolyte interphase, which is an important factor in the performance of LIBs. We expect that further investigation of the degradation products by LC/ESI-MS and ASAP-MS will be helpful for studying their degradation processes in LIBs. Copyright © 2016 John Wiley & Sons, Ltd.
TL;DR: No significant difference was observed between the results obtained by the present method and by a method using the same principle as the CEN-standard i.e. liquid-liquid extraction and post-column zinc reduction with fluorescence detection.
TL;DR: In this article, an innovative method for the characterization of the lipid composition in a complex and unknown vegetable oil: an extract of Kniphofia uvaria seeds; using Supercritical Fluid Chromatography (SFC) coupled to Atmospheric Pressure Chemical Ionization (APCI), High-Resolution Mass Spectrometry (HRMS) and UV detections.
TL;DR: The full chemical complement was for the first time reported for quality evaluation of Pinellia (P.) ternata and pedatisecta species and can be usefully applied for phytochemical analysis of related herbal medicines.
TL;DR: The topography and both the infrared and mass spectral chemical images showed that the valley regions of the thin film surface were comprised primarily of poly(2-vinylpyridine) and hill or plateau regions were primarily poly(methyl methacrylate), and the spatial resolution of the mass spectralchemical images was estimated to be 1.6 μm.
Abstract: In this paper, the use of a hybrid atomic force microscopy/infrared spectroscopy/mass spectrometry imaging platform was demonstrated for the acquisition and correlation of nanoscale sample surface topography and chemical images based on infrared spectroscopy and mass spectrometry. The infrared chemical imaging component of the system utilized photothermal expansion of the sample at the tip of the atomic force microscopy probe recorded at infrared wave numbers specific to the different surface constituents. The mass spectrometry-based chemical imaging component of the system utilized nanothermal analysis probes for thermolytic surface sampling followed by atmospheric pressure chemical ionization of the gas phase species produced with subsequent mass analysis. The basic instrumental setup, operation, and image correlation procedures are discussed, and the multimodal imaging capability and utility are demonstrated using a phase separated poly(2-vinylpyridine)/poly(methyl methacrylate) polymer thin film. The ...
TL;DR: The efficiency of charge exchange in both DA-APPI andDA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied and at increasing flow rate the abundance of chlorobenzene M+.
TL;DR: An in-vacuum plasma ionization source was designed and integrated into the system and an aerodynamic sampling method was developed to facilitate directional sample transfer towards the miniature mass spectrometer in an open environment.
Abstract: Previously, we have reported the development of a miniature mass spectrometer with a continuous atmospheric pressure interface (CAPI), and the use of it for non-volatile sample analysis, such as drugs, peptides and proteins. However due to the diffusion effects in the CAPI, especially stronger for light ions, the instrument shows low detection sensitivities for volatile samples when coupling with an atmosphere pressure chemical ionization (APCI) source (>ppmv). In this study, an in-vacuum plasma ionization source was designed and integrated into the system. By performing ionization in the first vacuum stage, ion transfer loss through the CAPI was minimized and tens of ppbv level detection sensitivities were achieved for volatile samples. Due to its improved sensitivity, chemical source tracing was demonstrated in an indoor environment as a simple proof-of-concept example. Furthermore, an aerodynamic sampling method was developed to facilitate directional sample transfer towards the miniature mass spectrometer in an open environment. By coupling this aerodynamic method with the miniature mass spectrometer, remote chemical source sensing could be achieved at a distance of more than two meters. This aerodynamic sampling method could also be applied to other mass spectrometry instruments for enhanced sample sampling in open environments.