Pressure Ionization Mass Spectrometry Research Articles

Computational analysis of the proton-bound acetonitrile dimer, (ACN)2 H.

In atmospheric pressure ionization mass spectrometry the theoretical thermodynamic treatment of proton-bound cluster stabilities helps us to understand the prevailing chemical processes. However, such calculations are rather challenging because low-barrier internal rotations and strong anharmonicity of the hydrogen bonds cause the breakdown of the usually applied harmonic approximation. Even the implemented anharmonic treatment in standard ab initio software failed in the case of (ACN)2 H+ . For a case study of the proton-bound acetonitrile dimer, (ACN)2 H+ , we scan the potential energy surface (PES) for the internal rotation and the proton movement in all three spatial directions. We correct the partition functions by treating the internal rotation as a free rotor and by solving the nuclear Schrödinger equation explicitly for the proton movement. An additional PES scan for the dissociation surface further improves the understanding of the cluster behavior. The internal rotation is essentially barrier free (V0 = 2.6 × 10-6 eV) and the proton's movement between the two nitrogen atoms follows a quartic rather than quadratic potential. As a figure of merit we calculate the free dissociation enthalpy of the dimer. Our description significantly improves the standard results from about 118.3 kJ/mol to 99.6 kJ/mol, compared with the experimentally determined value of 92.2 kJ/mol. The dissociation surface reveals strong crosstalk between modes and is essentially responsible for the observed errors. The presented corrections to the partition functions significantly improve their accuracy and are rather easy to implement. In addition, this work stresses the importance of alternative theoretical methods for proton-bound cluster systems besides the standard harmonic approximations.

Combining linear retention index and electron ionization mass spectrometry for a reliable identification in nano liquid chromatography

The present research is focused on the object to improve identification capability in liquid chromatography (LC), by creating a system as similar as possible to gas chromatography (GC), where the combination/complementarity of Linear Retention Index (LRI) and Electron Ionization Mass Spectrometry (EI-MS) data makes the identification process easy, automatic and reliable. Conversely, in LC the untargeted characterization of real-world samples is still a challenge, due to the not repeatable and poorly informative nature of typical atmospheric pressure ionization mass spectrometry, normally hyphenated to LC. In the last decades the miniaturization of LC instrumentation together with the considerable progresses in MS vacuum pump capability has made the LC-EI-MS hyphenation more feasible. In the present work, a prototypal nanoLC-EI-MS system was used for the determination of typically LC-amenable compunds, such as coumarins, furocoumarins and polymethoxyflavones in citrus essential oils. All the compounds provided high quality EI-MS spectra, evaluated by the comparison with thousands of spectra present in commercial EI-MS libraries. Spectral similarities major than 80% were achieved.Furthermore, an LRI system, based on the use of an alkyl aryl ketone homologue reference series, was proposed as additional filter to achieve a univocal identification. Then, a novel dual-filter LRI/EI-MS library was built and resulted very helpful in the case of isomeric compounds characterized by identical EI-MS spectrum, but different retention behaviour. The very low inter-day variability attained for each LRI value, together with the satisfactory chromatographic resolution of the developed method, led to a 100% reliability of the identification process based on LRI.

Atmospheric pressure mass spectrometric imaging of bio-tissue specimen using electrospray-assisted CW laser desorption and ionization source.

When a tissue slice pretreated with gold nanoparticles is irradiated with a focused 532-nm continuous wave laser, desorption is observed to be uniform and stable, and its shape is sharp and steep. However, since the desorbed molecules are still electrically neutral particles in atmospheric pressure (AP), additional procedure of ionizing them is necessary for AP mass spectrometry (AP-MS) analysis. Therefore, the authors have combined an electrospray device with a simple chamber connected to the airflow-assisted particle transport equipment mounted at the mass spectrometer inlet. Subsequent ionization processes using an electrospray device enable the detection of several types of diacylglycerol molecules above 500 Da, which cannot be detected with the use of AP plasma jets. The authors also developed a remote AP-MS using a long and flexible sampling probe and a fiber laser with a slight modification of the proposed AP desorption and ionization method.

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.

Considerations for uranium isotope ratio analysis by atmospheric pressure ionization mass spectrometry.

The accurate measurement of uranium isotope ratios from trace samples lies at the foundation of achieving nuclear nonproliferation. These challenging measurements necessitate both the continued characterization and evaluation of evolving mass spectrometric technologies as well as the propagation of sound measurement approaches. For the first time in this work, we present the analysis of uranium isotope ratio measurements from discrete liquid injections with an ultra-high-resolution hybrid quadrupole time-of-flight mass spectrometer. Also presented are important measurement considerations for evaluating the performance of this type and other atmospheric pressure and ambient ionization mass spectrometers for uranium isotope analysis. Specifically, as the goal of achieving isotope ratios from as little as a single picogram of solid material is approached, factors such as mass spectral sampling rate, collision induced dissociation (CID) potentials, and mass resolution can dramatically alter the measured isotope ratio as a function of mass loading. We present the ability to accurately measure 235UO2+/238UO2+ down to 10s of picograms of solubilized uranium oxide through a proper consideration of mass spectral parameters while identifying limitations and opportunities for pushing this limit further.

Single Layer Graphene Assisted Transmission Mode Continuous Wave Laser Desorption for Micrometer Spatial Resolution Atmospheric Pressure Mass Spectrometry Imaging

Single Layer Graphene Assisted Transmission Mode Continuous Wave Laser Desorption for Micrometer Spatial Resolution Atmospheric Pressure Mass Spectrometry Imaging

Degradation of the Neonicotinoid Pesticides in the Atmospheric Pressure Ionization Source.

During the analysis of neonicotinoid pesticide standards (thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid) by mass spectrometry, the degradation of these pesticides (M-C=N-R is degraded into M-C=O, M is the skeleton moiety, and R is NO2 or CN) was observed in the atmospheric pressure ionization interfaces (ESI and APCI). In APCI, the degradation of all the five neonicotinoid pesticides studied took place, and the primary mechanism was in-source ion/molecule reaction, in which a molecule of water (confirmed by use of H218O) attacked the carbon of the imine group accompanying with loss of NH2R (R=NO2, CN). For the nitroguanidine neonicotinoid pesticides (R=NO2, including thiamethoxam, clothianidin, and imidacloprid), higher auxiliary gas heater temperature also contributed to their degradation in APCI due to in-source pyrolysis. The degradation of the five neonicotinoid pesticides studied in ESI was not significant. In ESI, only the nitroguanidine neonicotinoid pesticides could generate the degradation products through in-source fragmentation mechanism. The degradation of cyanoamidine neonicotinoid pesticides (R=CN, including acetamiprid and thiacloprid) in ESI was not observed. The degradation of neonicotinoid pesticides in the ion source of mass spectrometer renders some adverse consequences, such as difficulty interpreting the full-scan mass spectrum, reducing the sensitivity and accuracy of quantitative analysis, and misleading whether these pesticides have degraded in the real samples. Therefore, a clear understanding of these unusual degradation reactions should facilitate the analysis of neonicotinoid pesticides by atmospheric pressure ionization mass spectrometry. Graphical Abstract.

Direct olive oil analysis by mass spectrometry: A comparison of different ambient ionization methods

Analytical methods based on ambient ionization mass spectrometry (AIMS) combine the classic outstanding performance of mass spectrometry in terms of sensitivity and selectivity along with convenient features related to the lack of sample workup required. In this work, the performance of different mass spectrometry-based methods has been assessed for the direct analyses of virgin olive oil for quality purposes. Two sets of experiments have been setup: (1) direct analysis of untreated olive oil using AIMS methods such as Low-Temperature Plasma Mass Spectrometry (LTP-MS) or paper spray mass spectrometry (PS-MS); or alternatively (2) the use of atmospheric pressure ionization (API) mass spectrometry by direct infusion of a diluted sample through either atmospheric pressure chemical ionization (APCI) or electrospray (ESI) ionization sources. The second strategy involved a minimum sample work-up consisting of a simple olive oil dilution (from 1:10 to 1:1000) with appropriate solvents, which originated critical carry over effects in ESI, making unreliable its use in routine; thus, ESI required the use of a liquid-liquid extraction to shift the measurement towards a specific part of the composition of the edible oil (i.e. polyphenol rich fraction or lipid/fatty acid profile). On the other hand, LTP-MS enabled direct undiluted mass analysis of olive oil. The use of PS-MS provided additional advantages such as an extended ionization coverage/molecular weight range (compared to LTP-MS) and the possibility to increase the ionization efficiency towards nonpolar compounds such as squalene through the formation of Ag+ adducts with carbon-carbon double bounds, an attractive feature to discriminate between oils with different degree of unsaturation.

Effects of liquid post-column addition in electrospray ionization performance in supercritical fluid chromatography–mass spectrometry

In supercritical fluid chromatography coupled to atmospheric pressure ionization mass spectrometry (SFC-MS), the use of a make-up post-column is almost mandatory to avoid analyte precipitation, especially when using low percentage of modifier (<5%) in the mobile phase. Due to the specific nature of gaseous CO2, the tuning of the make-up conditions in electrospray becomes an important factor and can be used to tune analyte sensitivity. Neither a dilution effect (loss of signal) nor a relevant degradation of chromatographic performances is observed with the addition of a make-up at various flow-rates, up to 0.7mL/min. From supercritical conditions (1mL/min 40°C, 150bar) to gaseous state (room temperature, atmospheric pressure), the CO2 expands around 430 times, contributing to almost 5% of the nebulizing process. In positive mode, the presence of ammonium ions either in the mobile phase or in the make-up did significantly increase the MS signal, even at basic apparent pH. The ionization performance of electrospray is influenced by the acidic buffer power of the carbon dioxide, and was found to be restricted in the apparent pH range of 3.8–7.2 in the various conditions investigated. This may challenge sensitive detection in negative mode, as illustrated for bosentan. The use of DMSO as make-up additive (up to 30%) showed a simplification of the full scan spectrum regarding the adducts. Finally, the optimization of make-up composition leads to an enhancement up to a factor of 69 on the electrospray MS response signal, for the SFC-SRM/MS analysis of HIV protease inhibitors in plasma extracted from Dried Plasma Spots.

Coupling supercritical fluid chromatography to positive ion atmospheric pressure ionization mass spectrometry: Ionization optimization of halogenated environmental contaminants

Currently used analytical techniques for halogenated aromatic environmental contaminants such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs), also known as legacy persistent organic pollutants, are based on gas chromatographic separation of target analytes and detection by mass spectrometry. The coupling of packed column supercritical fluid chromatography (SFC) to atmospheric pressure ionization mass spectrometry (API/MS) could allow for the concurrent analysis of thermally labile and legacy halogenated environmental contaminants if ionization can be sufficiently optimized. The evaluation of positive ion atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) as well as possible charge transfer dopants for the generation of molecular ion isotopomeric clusters of halogenated environmental contaminants with minimal fragmentation has been completed. Using the investigated parameters, positive ion APPI was found to be the more sensitive technique. Of the aromatic and cycloalkane dopants investigated, only fluorobenzene and trifluorotoluene were found to be effective dopants for the halogenated aromatic target analytes (PCDDs, PCDFs, and PCBs). Experiments involving deuterated dopants confirmed that reactive species generated by cycloalkanes were quenched by the SFC eluent rendering them unusable in conjunction with the investigated separation technique. Alternatively, aromatic dopants were found to be less susceptible to quenching by the SFC eluent and fluorobenzene was determined to be the most effective charge transfer dopant for PCDDs, PCDFs, and PCBs. To demonstrate the applicability of the optimized ionization conditions, SFC-API/MS has been used for the concurrent analysis of legacy halogenated aromatic environmental contaminants (PCDDs, PCDFs, and PCBs) and thermally labile analytes (α, β, and γ isomers of hexabromocyclododecane).

Abstract 4647: Mass spectrometric analysis of oncometabolite 2-hydroxyglutarate in clinical gliomas with the isocitrate dehydrogenase-1 mutation

Abstract Introduction: Mutations of the isocitrate dehydrogenase (IDH)-1/2 genes frequently occur in certain malignancies, including gliomas. Mutant IDH-1/2 proteins gain a new ability to produce oncometabolite 2-hydroxiglutarate (2HG), which results in a different clinical impact on gliomas in comparison to those with a wild-type IDH. The status of IDH mutations has been determined by immunohistochemistry (IHC) using the IDH1-R132H antibody or through the DNA sequencing of IDH1-R132C/R132S; however, its practical applications are still under discussion, and the significance of the oncometabolite 2HG evaluation is not clear. In this study, we analyzed the serum and tissue levels of 2HG in clinical gliomas using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and the matrix assisted laser desorption and ionization mass spectrometry imaging (MALDI-MSI) system. Method: Glioma samples (n = 78, matched pairs of serum and flash frozen tissue) were obtained between October 2007 to January 2015 at the National Cancer Center Hospital, Japan. High performance liquid chromatography (Nexera X2, Shimadzu) and triple quad mass spectrometry (QTRAP4500, AB SCIEX) were used for LC-MS/MS analysis. The two MALDI-MSI systems, quadrupole ion trap time-to-flight mass spectrometry imaging (iMScope, Shimadzu), and high-resolution atmospheric pressure mass spectrometry imaging (AP-SMALDI, TransMIT; Q-Exactive, Thermo Fisher Scientific) were used for analyzing the 2HG tissue distribution after coating with 9-aminoacridine or 2,5-dihydroxybenzoic acid. The IDH mutation was determined by direct sequencing and IHC. Results: The median 2HG concentration in serum was 21.43 ng/mL (range: 9.58 to 62.51) in this study, and no significant correlation was observed between the IDH mutation and the wild type status (mutation, n = 28, median 20.2 ng/mL, range 9.58 to 62.51 vs. wild type, n = 50, median 22.88 ng/mL, range 11.51 to 40.32; Wilcoxon test p = 0.1597). The median of the 2HG tissue concentration in the entire group was 0.16 ng/μg, and a significant difference was seen between the IDH mutant and wild type groups (mutation, median 4.86 ng/μg, range 0.51 to 49.86 vs. wild type, median 0.09 ng/μg, range 0.02 to 0.45; Wilcoxon test p = &amp;lt;0.0001). In the MALDI-MSI analysis, the average 2HG ion intensities were 381.62/mm2 in the IDH mutation and 8.25/mm2 in the wild-type IDH tissues (Wilcoxon test p = 0.016), which showed a positive correlation with the 2HG tissue concentration by LC-MSMS analyses (Spearman ρ = 0.87, p = 0.0003). The MSI results indicate a possible link between the 2HG tissue distributions and the histology of IDH mutant sections. Conclusion: Tissue 2HG measurement using mass spectrometric analyses may be a useful alternative in determining IDH mutations. Further research may provide a biological perspective and help gain some insights on the clinical significance of 2HG. Citation Format: Mitsuhiro Hayashi, Hiroaki Aikawa, Makoto Ohno, Koichi Ichimura, Yuko Matsushita, Mayu Ohuchi, Mariko Mizui, Akihiko Yoshida, Yoshitaka Narita, Akinobu Hamada. Mass spectrometric analysis of oncometabolite 2-hydroxyglutarate in clinical gliomas with the isocitrate dehydrogenase-1 mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4647. doi:10.1158/1538-7445.AM2017-4647

Rapid sample classification using an open port sampling interface coupled with liquid introduction atmospheric pressure ionization mass spectrometry.

An "Open Access"-like mass spectrometric platform to fully utilize the simplicity of the manual open port sampling interface for rapid characterization of unprocessed samples by liquid introduction atmospheric pressure ionization mass spectrometry has been lacking. The in-house developed integrated software with a simple, small and relatively low-cost mass spectrometry system introduced here fills this void. Software was developed to operate the mass spectrometer, to collect and process mass spectrometric data files, to build a database and to classify samples using such a database. These tasks were accomplished via the vendor-provided software libraries. Sample classification based on spectral comparison utilized the spectral contrast angle method. Using the developed software platform near real-time sample classification is exemplified using a series of commercially available blue ink rollerball pens and vegetable oils. In the case of the inks, full scan positive and negative ion ESI mass spectra were both used for database generation and sample classification. For the vegetable oils, full scan positive ion mode APCI mass spectra were recorded. The overall accuracy of the employed spectral contrast angle statistical model was 95.3% and 98% in case of the inks and oils, respectively, using leave-one-out cross-validation. This work illustrates that an open port sampling interface/mass spectrometer combination, with appropriate instrument control and data processing software, is a viable direct liquid extraction sampling and analysis system suitable for the non-expert user and near real-time sample classification via database matching. Published in 2016. This article is a U.S. Government work and is in the public domain in the USA.

Super-atmospheric pressure ionization mass spectrometry and its application to ultrafast online protein digestion analysis.

Pressure is a key parameter for an ionization source. In this Special Feature article, Lee Chuin Chen and colleagues review super-atmospheric pressure ionization MS with electrospray, corona-discharge-based chemical ionization, and field desorption. They routinely run their mass spectrometer with ion source pressures ranging from several to several tens of atmospheres. A number of strategies have been used to preserve the high vacuum of the instrument while working with a high-pressure (HP) ion source. A recent prototype uses a booster pump with variable pumping speed added to the first pumping stage of the mass spectrometer to regulate a constant vacuum pressure. Further, a new HP-ESI source allowing rapid (a few seconds) online protein digestion MS is also reported. Dr. Lee Chuin Chen is Associate Professor in the Department of Interdisciplinary Research at the University of Yamanashi (Yamanashi, Japan). His main research interest is the development of novel mass spectrometric methods for in-situ medical diagnosis.

Super-atmospheric pressure ionization mass spectrometry and its application to ultrafast online protein digestion analysis.

Ion source pressure plays a significant role in the process of ionization and the subsequent ion transmission inside a mass spectrometer. Pressurizing the ion source to a gas pressure greater than atmospheric pressure is a relatively new approach that aims to further improve the performance of atmospheric pressure ionization sources. For example, under a super-atmospheric pressure environment, a stable electrospray can be sustained for liquid with high surface tension such as pure water, because of the suppression of electric discharge. Even for nano-electrospray ionization (nano-ESI), which is known to work with aqueous solution, its stability and sensitivity can also be enhanced, particularly in the negative mode when the ion source is pressurized. A brief review on the development of super-atmospheric pressure ion sources, including high-pressure electrospray, field desorption and superheated ESI, and the strategies to interface these ion sources to a mass spectrometer will be given. Using a recent ESI prototype with an operating temperature at 220 °C under 27 atm, we also demonstrate that it is possible to achieve an online Asp-specific protein digestion analysis in which the whole processes of digestion, ionization and MS acquisition could be completed on the order of a few seconds. This method is fast, and the reaction can even be monitored on a near-real-time basis. Copyright © 2016 John Wiley & Sons, Ltd.

An open port sampling interface for liquid introduction atmospheric pressure ionization mass spectrometry.

A simple method to introduce unprocessed samples into a solvent for rapid characterization by liquid introduction atmospheric pressure ionization mass spectrometry has been lacking. The continuous flow, self-cleaning open port sampling interface introduced here fills this void. The open port sampling interface used a vertically aligned, co-axial tube arrangement enabling solvent delivery to the sampling end of the device through the tubing annulus and solvent aspiration down the center tube and into the ionization source of the mass spectrometer via the commercial APCI emitter probe. The solvent delivery rate to the interface was set to exceed the aspiration rate, creating a continuous sampling interface along with a constant, self-cleaning spillover of solvent from the top of the probe. Using the open port sampling interface with positive ion mode APCI and a hybrid quadrupole time-of-flight mass spectrometer, rapid, direct sampling and analysis possibilities are exemplified with plastics, ballpoint and felt tip ink pens, skin, and vegetable oils. These results demonstrated that the open port sampling interface could be used as a simple, versatile and self-cleaning system to rapidly introduce multiple types of unprocessed, sometimes highly concentrated and complex, samples into a solvent flow stream for subsequent ionization and analysis by mass spectrometry. The basic setup presented here could be incorporated with any self-aspirating liquid introduction ionization source (e.g., ESI, APCI, APPI, ICP, etc.) or any type of atmospheric pressure sampling-ready mass spectrometer system. The open port sampling interface provides a means to introduce and quickly analyze unprocessed solid or liquid samples with the liquid introduction atmospheric pressure ionization source without fear of sampling interface or ionization source contamination.

Mixed copper–platinum complex formation could explain synergistic antiproliferative effect exhibited by binary mixtures of cisplatin and copper-1,10-phenanthroline compounds: An ESI–MS study

Cisplatin, cis-diammineplatinum(II) dichloride, is a metal complex used in clinical practice for the treatment of cancer. Despite its great efficacy, it causes adverse reactions and most patients develop a resistance to cisplatin. To overcome these issues, a multi-drug therapy was introduced as a modern approach to exploit the drug synergy. A synergistic effect had been previously found when testing binary combinations of cisplatin and three copper complexes in vitro, namely, Cu(phen)(OH2)2(OClO3)2, [Cu(phen)2(OH2)](ClO4)2 and [Cu(phen)2(H2dit)](ClO4)2,(phen=1,10-phenanthroline, H2dit=imidazolidine-2-thione), against the human acute T-lymphoblastic leukaemia cell line (CCRF-CEM). In this work [Cu(phen)2(OH2)](ClO4)2 was also tested in combination with cisplatin against cisplatin-resistant sublines of CCRF-CEM (CCRF-CEM-res) and ovarian (A2780-res) cancer cell lines. The tested combinations show a synergistic effect against both the types of resistant cells. The possibility that this effect was caused by the formation of new adducts was considered and mass spectra of solutions containing cisplatin and one of the three copper complexes at a time were measured using electrospray ionisation at atmospheric-pressure mass spectrometry (ESI–MS). A mixed complex was detected and its stoichiometry was assessed on the basis of the isotopic pattern and the results of tandem mass spectrometry experiments. The formed complex was found to be [Cu(phen)(OH)μ-(Cl)2Pt(NH3)(H2O)]+.

Pyroelectricity Assisted Infrared-Laser Desorption Ionization (PAI-LDI) for Atmospheric Pressure Mass Spectrometry.

A new atmospheric pressure ionization method termed pyroelectricity-assisted infrared laser desorption ionization (PAI-LDI) was developed in this study. The pyroelectric material served as both sample target plate and enhancing ionization substrate, and an IR laser with wavelength of 1064 nm was employed to realize direct desorption and ionization of the analytes. The mass spectra of various compounds obtained on pyroelectric material were compared with those of other substrates. For the five standard substances tested in this work, LiNbO3 substrate produced the highest ion yield and the signal intensity was about 10 times higher than that when copper was used as substrate. For 1-adamantylamine, as low as 20 pg (132.2 fmol) was successfully detected. The active ingredient in (Compound Paracetamol and 1-Adamantylamine Hydrochloride Capsules), 1-adamantylamine, can be sensitively detected at an amount as low as 150 pg, when the medicine stock solution was diluted with urine. Monosaccharide and oligosaccharides in Allium Cepa L. juice was also successfully identified with PAI-LDI. The method did not require matrix-assisted external high voltage or other extra facility-assisted set-ups for desorption/ionization. This study suggested exciting application prospect of pyroelectric materials in matrix- and electricity-free atmospheric pressure mass spectrometry research.

Electrospray ionization for determination of non-polar polyaromatic hydrocarbons and polyaromatic heterocycles in heavy crude oil asphaltenes.

Electrospray ionization (ESI) is the most common ionization method in atmospheric pressure ionization mass spectrometry because of its easy use and handling and because a diverse range of components can be effectively ionized from high to medium polarity. Usually, ESI is not employed for the analysis of non-polar hydrocarbons, but under some circumstances, they are effectively ionized. Polyaromatic hydrocarbons and aromatic heterocycles can form radical ions and protonated molecules after ESI, which were detected by Fourier transform ion cyclotron resonance mass spectrometry. The highly condensed aromatic structures are obtained from a heavy crude oil, and the results show class distribution from pure hydrocarbons up to more non-basic nitrogen-containing species. By using different solvent compositions [toluene/methanol (50/50 v/v), dichloromethane/methanol (50/50 v/v), dichloromethane/acetonitrile (50/50 v/v) and chloroform], the results show that the lack of proton donor agent helps to preserve the radical formation that was created at the metal/solution interface inside the electrospray capillary. The results demonstrate that with an appropriate selection of solvent and capillary voltage, the ratio between the detected radical ion and protonated molecule form can be manipulated. Therefore, ESI can be expanded for the investigation of asphaltene and other polyaromatic systems beyond the polar constituents as non-polar hydrocarbons can be efficiently analyzed.

Plasma ionization source for atmospheric pressure mass spectrometry imaging using near-field optical laser ablation.

Mass spectrometry imaging (MSI) at ambient pressures with submicrometer resolution is challenging, due to the very low amount of material available for mass spectrometric analysis. In this work, we present the development and characterization of a method for MSI based on pulsed laser ablation via a scanning near-field optical microscopy (SNOM) aperture tip. SNOM allows laser ablation of material from surfaces with submicrometer spatial resolution, which can be ionized for further chemical analysis with MS. Efficient ionization is realized here with a custom-built capillary plasma ionization source. We show the applicability of this setup for mass spectrometric analysis of three common MALDI matrices, α-4-hydroxycyanocinnamic acid, 3-aminobenzoic acid, and 2,5-dihydroxybenzoic acid. Although the ultimate goal has been to optimize sensitivity for detecting material ablated from submicrometer diameter craters, the effective lateral resolution is currently limited by the sensitivity of the MS detection system. In our case, the sensitivity of the MS was about 1 fmol, which allowed us to achieve a spatial resolution of 2 μm. We also characterize the analytical figures of merit of our method. In particular, we demonstrate good reproducibility, a repetition rate in the range of only a few seconds, and we determined the amount of substance required to achieve optimal resolution and sensitivity. Moreover, the sample topography is available from SNOM scans, a parameter that is missing in common MSI methods.

Analytical Performance of LC-MS/MS Method for Simultaneous Determination of Five Steroids in Serum

The accurate measurement of steroid hormones is the fulcrum of modern endocrinology. Our aim was to develop a mass spectrometry coupled with a liquid chromatographic method for 17-hydroxyprogesterone, androstenedione, 11-desoxycortisol, 21-desoxycortisol and cortisol serum quantification simultaneously. The samples were submitted to isotopic internal standards addition, protein precipitation and two dimensional liquid chromatography consisting of trapping column and reverse-phase C18 analytical column following atmospheric pressure chemical ionization and mass spectrometry detection. For all compounds tested functional sensitivity was less than 0.5 ng/mL, precision was less than 15%, recovery ranged from 93% to 120%, linearity ranged from 89% to 111%, and accuracy was considered adequate. In conclusion, we developed a suitable, fast and reliable method for simultaneous routine measurement of 17-hydroxyprogesterone, androstenedione, 11-desoxycortisol, 21-desoxycortisol and cortisol in serum.