Pressure Electrospray Ionization Research Articles

Profiling Murchison Soluble Organic Matter for New Organic Compounds with APPI- and ESI-FT-ICR MS.

The investigation of the abundant organic matter in primitive meteorite such as carbonaceous chondrites is of major interest in the field of origin of life. In this study, the soluble organic fraction of the Murchison meteorite was analyzed by atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), in both detection modes. Such an approach ensured that we obtained an extensive description of the organic matter of the CM2 meteorite. Indeed, while in total close to 16,000 unique features were assigned, only 4% are common to all analyses, illustrating the complementarity of both the detection modes and the ionization sources. ESI FT-ICR MS analysis, in negative-ion mode, ensured to observe specifically CHOS and CHNOS species, whereas the positive-ion mode is more dedicated to the detection of CHNO and CHN species. Moreover, new organomagnesium components were observed in (+) ESI. Eventually, (+) APPI FT-ICR MS analysis was a preferred method for the detection of less polar or nonpolar species such as polycyclic aromatic hydrocarbons but also heteroatom aromatic species composing the organic matter of Murchison.

Molecular-level investigation of soils contaminated by oil spilled during the Gulf War.

In this study, molecular-level chemical compositions of soils contaminated by oil spilled during the Gulf War were studied. Two soil samples, respectively collected at 0.1 m and between 0.5 and 1 m below the surface from an oil spill site, were extracted with organic solvents and water. The extracts were analyzed via ultrahigh resolution FT-ICR and two-dimensional gas chromatography/high resolution mass spectrometry. The data showed that the spilled oil was significantly affected by vaporization due to high surface temperatures in the desert. The data obtained with (+) atmospheric pressure photo ionization (APPI) and (-) electrospray ionization (ESI) coupled with ultrahigh resolution-mass spectrometry (UHR-MS) indicated that the degradation of aromatic compounds and increase in oxygen-containing classes occurred in the following order: surface soil > below surface soil > crude oil. The oxygenated compounds were confirmed by principal component analysis. The score and loading plots of Ox and SOx showed that they were the major contributors to differentiate the samples. However, a comparison with previously reported oceanic oil spills showed that less significant degradation occurred even after almost 30 years. Our data can provide an information basis for designing a strategy for clean-up and restoration efforts of Gulf War oil spills.

Comparative limitations and benefits of liquid chromatography – mass spectrometry techniques for analysis of sex steroids in tears

Sex steroids impact regulation of the ocular surface tissues and thus influence dry eye. Most tissues in the human body synthesise and metabolise active sex steroids at levels required by the tissue. This is likely to also be the case for humans in ocular surface tissues. This study investigated the presence and quantities of selected sex steroids, in addition to sex steroid precursors and metabolites, in human tears. Detection of sex steroids in tears is challenging due to trace level analyte concentrations and low volumes of available tears. Immunoassays have previously been employed to assess sex steroids in tears, however, this approach only allows a single analyte to be measured and can overestimate concentrations. This study evaluated ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) and tandem mass spectrometry (MS/MS) methods for the concurrent detection and estimation of fourteen sex steroid and metabolite compounds in human tears.Basal tears were collected and pooled from 5 healthy pre-menopausal women (total 100 μL). Following protein precipitation and centrifuging, extract volumes equivalent to 14 μL of pooled tears were analysed.A Thermo Scientific Q Exactive™ Plus MS was used to compare novel high-resolution MS atmospheric pressure chemical ionization (APCI) and electrospray ionisation (ESI) methods for detection of fourteen target sex steroids, including dehydroepiandrosterone–sulphate (DHEAS), testosterone, oestradiol and their metabolites, using standards and pooled tears. The MS was programmed to switch between positive and negative polarity ionization modes at designated times through the UPLC run, in order to detect each analyte at optimal sensitivity. Analytes were analysed using APCI in standard mixtures at concentrations of 0.1, 0.3, 1, 3, 10, 30, 100 and 1000 pg/mL, per component, to determine the limits of detection (LOD) and quantification. Both parallel reaction monitoring (PRM) MS/MS and selected ion monitoring (SIM) MS, were evaluated by plotting narrow range mass-to-charge ratio (m/z) chromatograms for each analyte.An APCI UPLC-MS method to simultaneously measure 14 sex steroids using standards was successfully developed following comparative evaluation of all available LC-MS techniques. Preliminary experiments found APCI to be more sensitive than ESI using standards. Narrow m/z range SIM MS resulted in better sensitivity, in tear samples, than PRM. One sex steroid and two androgen metabolites were detected, with the developed APCI UPLC-MS method, and their concentrations estimated in human tears that had been extracted with a protein crash. Progesterone, androsterone–glucuronide (ADT-G) and 3αDiol-G were successfully detected in the tear extract and their concentrations in the pooled tear sample were estimated (with 95% confidence intervals) to be 0.10 ± 0.03 pg/μL, 30.9 ± 18.3 pg/μL and 9.8 ± 4.3 pg/μL respectively. The concentrations of the remaining 11 sex steroids in the tear sample were below the LODs of the method.This work shows that high mass resolution UPLC-MS can detect certain sex steroids and metabolites in tears, but that sensitivity of the technique and the low available tear volumes limit its application to a broader range of sex steroids. The investigation of sex steroids in tears and ocular surface tissue will aid understanding of the influence of sex steroids on ocular surface tissues facilitating better targeted treatment for dry eye.

Comprehensive Molecular Characterization of Atmospheric Brown Carbon by High Resolution Mass Spectrometry with Electrospray and Atmospheric Pressure Photoionization.

Light-absorbing components of atmospheric organic aerosols, which are collectively termed "brown carbon" (BrC), are ubiquitous in the atmosphere. They affect absorption of solar radiation by aerosols in the atmosphere and human health as some of them have been identified as potential toxins. Understanding the sources, formation, atmospheric evolution, and environmental effects of BrC requires molecular identification and characterization of light-absorption properties of BrC chromophores. Identification of BrC components is challenging due to the complexity of atmospheric aerosols. In this study, we employ two complementary ionization techniques, atmospheric pressure photo ionization (APPI) and electrospray ionization (ESI), to obtain broad coverage of both polar and nonpolar BrC components using high-resolution mass spectrometry (HRMS). These techniques are combined with chromatographic separation of BrC compounds with high performance liquid chromatography (HPLC), characterization of their light absorption with a photodiode array (PDA) detector, and chemical composition with HRMS. We demonstrate that this approach enables more comprehensive characterization of BrC in biomass burning organic aerosols (BBOAs) emitted from test burns of sage brush biofuel. In particular, we found that nonpolar BrC chromophores such as PAHs are only detected using positive mode APPI. Meanwhile, negative mode ESI results in detection of polar compounds such as nitroaromatics, aromatic acids, and phenols. For the BrC material examined in this study, over 40% of the solvent-extractable BrC light absorption is attributed to water insoluble, nonpolar to semipolar compounds such as PAHs and their derivatives, which require APPI for their identification. In contrast, the polar, water-soluble BrC compounds, which are detected in ESI, account for less than 30% of light absorption by BrC.

Aromatic formulas in ambient PM2.5 samples from Hong Kong determined using FT-ICR ultrahigh-resolution mass spectrometry.

Many aromatic compounds (e.g., polycyclic aromatic hydrocarbons (PAHs)) found in atmospheric aerosols are toxic and exist in both unsubstituted and substituted forms. Previous studies have mainly concentrated on investigating unsubstituted PAHs, leaving the substituted compounds largely uncharacterized. This study focuses on detection of both unsubstituted and substituted aromatics in ambient aerosol samples using ultrahigh-resolution mass spectrometry. Aerosol samples collected from roadside, urban, and suburban sites in Hong Kong were characterized by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) coupled with atmospheric pressure photoionization (APPI) or electrospray ionization (ESI). In the APPI+ mode, 166 aromatic CH formulas (i.e., formulas containing C and H only and with a double bond equivalent (DBE) of 4 or higher) were determined through molecular formula calculations based on an accurate m/z determination. Among the determined aromatic CH formulas, 141 are possible alkylated monocyclic aromatic hydrocarbon (MAH) or PAH formulas, and account for ≥ 45% of the total intensity by aromatic CH+ formulas. Both APPI+ and ESI+ are effective in detecting nitroaromatics (i.e., CHO2N1 formulas and DBE ≥ 5). The two ionization modes provide complementary formula coverage, with formulas determined by APPI+ extending to higher DBE and those by ESI+ covering higher carbon numbers. Alkylated nitrobenzene compounds are the most abundant among nitroaromatics, and they, together with alkylated nitro-PAHs, account for > 80% of the total intensity of aromatic CHO2N+ formulas, indicating the importance of these compounds in real aerosol samples. Aromatic CHN+ and CHO+ formulas are also determined, confirming the atmospheric presence of some previously reported O- and N-containing aromatic compounds and revealing new possible formulas. The determination of aromatic organic formulas in this study provides useful guidance for future quantitative analysis of hazardous aromatic compounds. Future work is needed to determine the abundance and to study the toxicity of alkylated MAHs and PAHs outside the 16 US EPA priority PAH compounds. Graphical abstract.

Insight into the molecular distribution of soluble components from Dayan lignite through mass spectrometers with four ionization methods

Dayan lignite (DL) was subjected to thermal dissolution sequentially with cyclohexane, acetone and methanol to obtain three filtrates. The filtrates were characterized by Fourier transform infrared spectroscopy, gas chromatography/mass spectrometry (GC/MS), and time-of-flight mass spectrometry (TOF-MS) equipped with atmospheric pressure photoionization (APPI), electrospray ionization (ESI) or direct analysis in real time (DART) to understand the structural features of DL. Aliphatic hydrocarbons, furans and alcohols were enriched in the filtrate of cyclohexane, acetone and methanol, respectively, according to the data of GC/MS. One ring aromatics was also identified by GC/MS as major species in the three filtrates. Both GC/MS and APPI-MS can well analyze compounds with low polarity, but APPI-TOF-MS in this work successfully characterized polycyclic aromatics and extended the measurement range (molecular weight and ring size) of GC/MS. ESI-TOF-MS is suitable to analyze polar compounds in coal. Data from ESI-TOF-MS indicated that heteroatom compounds including non-aromatics and aromatics with 1-2 rings are the major polar components in DL. As an ambient MS ionization method, DART shortened the analysis time without sample pretreatment and more aromatics over 4 rings were identified by DART-TOF-MS. Characterization of the complex coal filtrates with multiple mass spectrometers provided a full view of the molecular information of DL.

Detailed Compositional Characterization of the 2014 Bangladesh Furnace Oil Released into the World’s Largest Mangrove Forest

On December 9, 2014, ∼94 000 gallons of furnace oil spilled into the Shela River in Bangladesh, a designated World Heritage Site by the United Nations Educational, Scientific and Cultural Organization. It was the largest recorded oil spill in the Sundarbans region. Visually, furnace oil appears similar to heavy fuel oil, but little is known about its composition even though it is heavily utilized worldwide. A shift in global oil production to heavier, less well-known feeds (i.e., heavy oil and bitumen) requires molecular-level knowledge for efficient response, damage assessment, and restoration in the event of any oil spill. However, little is known about the chemical composition of furnace oil in chronic and acute releases. For the first time, we catalog the molecular-level composition of a relatively unknown furnace oil collected immediately after the 2014 Bangladesh spill and compare it to a well-characterized intermediate fuel oil (IFO) spilled in Texas City, Texas (U.S.A.) in March 2014. Through a combined technique approach, we apply comprehensive two-dimensional gas chromatography (GC×GC) analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to contrast the unknown furnace oil to IFO. Combined, these techniques capture the continuum of oil components and access the less volatile, highly complex non-GC amenable compounds. GC×GC analysis provides biomarker signatures that suggest the furnace oil likely originated in the Middle East and is a refined product. We further compared the furnace oil with the Arabian light crude from Middle East origin (WP681) and revealed remarkable similarities between the two oils. Simulated distillation for the furnace oil showed that 42% of the oil mass is not volatile below 478 °C (equivalent to C40; the upper limit for GC-based techniques), whereas the IFO contained 38% of the total mass >C40. Furthermore, FT-ICR MS extends the carbon number range and unlocks the molecular composition of non-GC amenable compounds. Atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) FT-ICR MS resolve and identify tens of thousands of molecular formulas in each oil and report furnace oil composition similar to whole heavy crudes. To the best of our knowledge, this is the first report of the detailed compositional characterization of any furnace oil.

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.

Quantitative Analysis of Bisphenol A in Recycled Paper with a Novel Direct Inlet Probe-Atmospheric Pressure Photoionization–IonTrap-MS

A new ambient ion source was developed and its application to real samples has been demonstrated. This ion source is based on a previously build ion source using chemical ionization under atmospheric pressure and extractive electrospray ionization (DIP-APCI/EESI). To enhance the range of analytes, we added to this ion source a photoionization lamp to enable also photoionization, which allows the possibility to analyze polar (EESI), middle (APCI) and non-polar (APPI) analytes with the same source and with no or only a small change of the setup. In comparison with DIP-APCI, this ion source reaches similar analytical limits but shows better sensitivity for some aromatic and non-polar analytes. The analysis of bisphenol A from extracts of recycled paper demonstrates the use of this ion source for real samples. Quantification was possible by the use of a deuterated internal standard that was added to the papers before extraction. Here atmospheric pressure chemical ionization leads to bad results due to ion suppression, whereas atmospheric pressure photoionization shows results that fit to literature values.

Żółte barwniki organiczne w XIX-wiecznych farbach Jana Matejki – identyfikacja substancji barwiących, nośników oraz wypełniaczy

Natural organic dyes can be found in many objects of cultural heritage. Identification of coloring substances present in historical paints provides relevant information for a wide range of specialists involved in art science. Determination of the composition of paints allows application of appropriate procedures for restoration and conservation of historical works of art. This information enables treatment in accordance with the ideological and esthetic decisions of the authors. The complexity of the chemical composition of art paints, which, apart from organic dyes can also include inorganic pigments, binders and other additives, hinders isolation and identification of its individual components. Nowadays, there are several analytical techniques and methods for extraction and identification of organic dyes, each of them has its limitations, however. For that reason, the development of the universal methodology for the analysis of colorant composition in art paints remains a challenge for chemists. In present work, an analytical protocol for identification of yellow dyes using reversed phase liquid chromatographymass spectrometry with atmospheric pressure electrospray ionization (LC-ESI/ /MS) is presented. The developed method was successfully applied to identification of the main components of Indian Yellow, weld ( Reseda luteola L.), buckthorn berries ( Rhamnus ) and madder lake (madder plant’s root) extracts, in the historical oil paints from tubes of Richard Aines company, formerly Mulard, owned before him by recognizable French art materials supplier Eduard. The recognition of paints composition was broadened by identification of non organic compounds – carriers of the dye: aluminum hydroxide, tin chloride, chalk, as well as filler like silica and or lead white. Researched samples of painting materials belonged to 19th century famous Polish painter Jan Matejko (1839–1893) and will be very helpful in understanding paintings of him and of his contemporaries.

Predicting collision-induced dissociation mass spectra: understanding the role of the mobile proton in small molecule fragmentation.

Intramolecular proton migration has been reported to be required for fragmentation by collision-induced dissociation (CID). If the collision energy is required to provide energy for proton movement to a ‘dissociative’ site, it may be possible to predict the optimal collision energy for fragmentation using quantum computational chemistry software. A greater understanding of the mechanism(s) of proton migration is necessary. The product ion spectra of seven compounds were obtained at collision energies stepped in the range from 5 to 50 eV, with precursor ions being generated in positive ion mode by both atmospheric pressure chemical ionization (APCI) and electrospray ionisation (ESI) (using an ESCi ionisation source with or without corona discharge, respectively). The products ions observed at each collision energy were assessed in terms of structure to ascertain if they were formed as a result of protonation at the initial ionisation site or if the proton had migrated to a dissociative site. Proton migration was shown to be independent of collision energy, stability of the protonated molecule and the distance that the proton moved. Therefore, proton migration is not a barrier to fragmentation as the proton appears to be fully mobile at 5 eV. As proton migration is independent of collision energy for these compounds, whereas fragmentation is energy dependent, protonation at the dissociative site alone is not sufficient to cause bond cleavage. The role of collision energy in bond cleavage may be to increase the vibrational energy of the bond and/or increase the rate of bond cleavage such that it occurs within the residence time of the ion within the collision cell rather than to supply the energy for proton migration. Therefore, quantum chemistry alone cannot predict the collision energies appropriate for fragmentation on the basis of modelling proton movements.

Non-detection of C60 fullerene at two mass extinction horizons

Fullerene (C60) have been reported in a number of geologic samples and, in some cases, attributed to carbonaceous materials delivered during bolide impact events. The extraction and detection of C60 poses significant analytical challenges, and some studies have been called into question due to the possibility of C60 forming in situ. Here, we extracted samples taken from the Permian–Triassic boundary section in Meishan, South China and the Cretaceous–Paleogene boundary exposed at Stevns Klint, Denmark, and analyzed the residues using a fast and reliable method for quantifying C60. Extraction of both whole rock and completely demineralized samples were completed under conditions that previously yielded C60 as well as using an optimized approach based on recent literature reports. These extracts were analyzed using mass spectrometry with the soft-ionization techniques, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), which have not been shown to form fullerenes in-situ. In no case were we able to detect C60, nor could we corroborate previous reports of its occurrence in these sediments, thereby challenging the utility of fullerene as a proxy for bolide impacts or mass extinction events.

Molecular characteristics of a Chinese coal analyzed using mass spectrometry with various ionization modes

Abstract A Xinjiang subbituminous coal was directly oxidized in aqueous sodium hypochlorite and sequentially extracted with diethyl ether and ethyl acetate. The extracts were esterified with diazomethane and the esterified products were analyzed using a high performance liquid chromatograph/mass spectrometer (HPLC/MS) equipped with atmospheric pressure photoionization (APPI) or electrospray ionization (ESI) ion source. Toluene and a toluene/anisole mixture (vol/vol = 95:5) were used as dopant for APPI-MS. The relative of organic species with molecular mass over 500 u detected by ESI-MS is much higher than that identified by APPI-MS with and without dopant. The addition of dopant greatly enhanced the ionization efficiency and toluene induced better ionization effects compared to the mixture in both ion signal intensity and number of detected species. However, according to the ionization mechanism of APPI, a small portion of analytes could be well ionized under direct APPI mode rather than dopant-assisted mode.

Identification and characterization of the Indian Yellow dyestuff and its degradation products in historical oil paint tube by liquid chromatography mass spectrometry

An analytical protocol for identification of dyes using reversed phase liquid chromatography-mass spectrometry with atmospheric pressure electrospray ionization (LC-ESI/MS) is presented.

Enhanced detection of the algal toxin PbTx-2 in marine waters by atmospheric pressure chemical ionization mass spectrometry.

Karenia brevis, a marine dinoflagellate, biosynthesizes a unique class of polyether toxins called brevetoxins that produce significant health, environmental and economic impacts in and along coastal waters. Previous application of liquid chromatography/mass spectrometry for detection of the most common brevetoxin, PbTx-2, has relied almost exclusively upon electrospray ionization (ESI). A different ionization source is proposed in this study with improved sensitivity ultimately leading to lower limit of detection compared to (+) ESI. Brevetoxin standards and samples (PbTx-2) were analyzed by liquid chromatography/mass spectrometry using both (+) atmospheric pressure chemical ionization and (+) electrospray ionization sources. LC/MS with (+) APCI exhibited an order of magnitude improvement in the limit of detection (7.7 × 10(-4) pg mass on-column) compared to the same method using (+) ESI (7.5 × 10(-3) pg mass on-column). The calibration sensitivity of (+) APCI (1.3 × 10(3)) was also five times higher than positive mode (+) ESI (0.26 × 10(3)). Positive mode APCI represents a significant improvement in detection and quantification of PbTx-2 by LC/MS allowing for smaller sample sizes compared to previous studies using (+) ESI. This in turn leads to higher throughput of samples during and after bloom events giving stakeholders detailed information on the fate of this potent marine toxin.

Development of a liquid chromatography-tandem mass spectrometry method for determination of butoconazole nitrate in human plasma and its application to a pharmacokinetic study.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the determination of butoconazole in human plasma. Human plasma samples of 0.2 μL were pretreated by a single step protein precipitation procedure and analyzed using a high performance liquid chromatography (HPLC) electrospray tandem mass spectrometer system. The compounds were eluted isocratically on an Inertsil ODS-SP column (100 mm×2.1 mm, 3 μm), ionized using a positive ion atmospheric pressure electrospray ionization source and analyzed using multiple reaction monitoring (MRM) mode. The ion transitions monitored were m/z 412.8→165.1 for butoconazole and m/z 453.4→230.3 for the internal standard. The chromatographic run time was 3.5 min per injection, with retention time of 2.47 min and 2.15 min for butoconazole and repaglinide, respectively. The method was validated to be linear over the range of 20 to 8000 pg/mL (r>0.999) by using a weighted (1/x(2)) quadratic regression. The mean recovery rate was more than 86.7%, and the intra- and inter-day precision of the quality control samples (QCs) was less than 8.3% and the accuracy ranged from 96.0% to 110.2%, which indicated that the quantitative method was reliable and accurate. The method is simple, rapid, and has been applied successfully to a pharmacokinetics study of butoconazole nitrate suppositories in healthy Chinese females.

New insights into the extraction of uranium(VI) by an N,N-dialkylamide

This paper presents the methodology developed in order to thoroughly characterise a solvent extraction system containing high solute concentrations. The chemical system selected is N,N-(2-ethylhexyl)isobutyramide (DEHiBA) diluted in one alkane with increasing concentration of uranium(VI). Combining experiments with theoretical calculations allowed a deeper understanding of the extraction mechanism. A thermodynamic study was performed by the classical van't Hoff method and also by direct calorimetry to provide the enthalpies of extraction and specific heats. Dedicated methods like vapour pressure osmometry and electrospray ionisation mass spectrometry analysis provide information about the stoichiometry of the extracted species. Spectroscopic investigations with ultraviolet–visible and Fourier transform infrared probed the uranium coordination. Finally, a combination of molecular dynamics simulations, and small and wide-angle X-ray scattering experiments investigated the organisation in the organic phase beyond the molecular scale. It was shown that the high concentrations of uranium extracted have no influence on the stoichiometry of the complexes and the coordination of uranium in the inner sphere. The thermodynamic properties related to the extraction process and obtained with a fine consideration of the activity coefficients showed to be the same as those found with trace concentration. However, an unexpected organisation beyond the molecular scale was observed with an important role of nitrates as bridging ligands which could explain some physico-chemical properties. This approach could be applied to other chemical systems (other N,N-dialkylamides or other cations) to identify the origin of the different affinities between ligands and the difference of selectivity between cations.

Simultaneous determination of volatile and non-volatile nitrosamines in processed meat products by liquid chromatography tandem mass spectrometry using atmospheric pressure chemical ionisation and electrospray ionisation

A sensitive, selective and generic method has been developed for the simultaneous determination of the contents (μgkg−1 range) of both volatile nitrosamines (VNA) and non-volatile nitrosamines (NVNA) in processed meat products. The extraction procedure only requires basic laboratory equipment and a small volume of organic solvent. Separation and quantification were performed by the developed LC–(APCI/ESI)MS/MS method. The method was validated using spiked samples of three different processed meat products. Satisfactory recoveries (50–130%) and precisions (2–23%) were obtained for eight VNA and six NVNAs with LODs generally between 0.2 and 1μgkg−1, though for a few analyte/matrix combinations higher LODs were obtained (3 to 18μgkg−1). The validation results show that results obtained for one meat product is not always valid for other meat products. We were not able to obtain satisfactory results for N-nitrosohydroxyproline (NHPRO), N-nitrosodibenzylamine (NDBzA) and N-nitrosodiphenylamine (NDPhA). Application of the APCI interface improved the sensitivity of the method, because of less matrix interference, and gave the method a wider scope, as some NAs were ionisable only by APCI. However, it was only possible to ionize N-nitroso-thiazolidine-4-carboxylic acid (NTCA) and N-nitroso-2-methyl-thiazolidine-4-carboxylic acid (NMTCA) by ESI. The validated method was applied for the analysis of processed meat products and contents of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosomethylaniline (NMA), N-nitrosoproline (NPRO), NTCA, and NMTCA were found in one or several nitrite cured meat products, whereas none were detected in non-nitrite cured bacon.

Low‐mobility‐pass filter between atmospheric pressure chemical ionization and electrospray ionization sources and a single quadrupole mass spectrometer: computational models and measurements

Mixtures of ions produced in sources at atmospheric pressure, including chemical ionization (APCI) and electrospray ionization (ESI) can be simplified at or near ambient pressure using ion mobility based filters. A low-mobility-pass filter (LMPF) based on a simple mechanical design and simple electronic control was designed, modeled and tested with vapors of 2-hexadecanone in an APCI source and with spray of peptide solutions in an ESI source. The LMPF geometry was planar and small (4 mm wide × 13 mm long) and electric control was through a symmetric waveform in low kHz with amplitude between 0 and 10 V. Computational models established idealized performance for transmission efficiency of ions of several reduced mobility coefficients over the range of amplitudes and were matched by computed values from ion abundances in mass spectra. The filter exhibited a broad response function, equivalent to a Bode Plot in electronic filters, suggesting that ion filtering could be done in blocks ~50 m/z units wide. The benefit of this concept is that discrimination against ions of high mobility is controlled by only a single parameter: waveform amplitude at fixed frequency. The effective removal of high mobility ions, those of low mass-to-charge, can be beneficial for applications with ion-trap-based mass spectrometers to remove excessive levels of solvent or matrix ions.

Quadruple parallel mass spectrometry for analysis of vitamin D and triacylglycerols in a dietary supplement

A “dilute-and-shoot” method for vitamin D and triacylglycerols is demonstrated that employed four mass spectrometers, operating in different ionization modes, for a “quadruple parallel mass spectrometry” analysis, plus three other detectors, for seven detectors overall. Sets of five samples of dietary supplement gelcaps labeled to contain 25.0μg (1000 International Units, IU) vitamin D3 in olive oil were diluted to 100mL and analyzed in triplicate by atmospheric pressure chemical ionization (APCI) mass spectrometry (MS), atmospheric pressure photoionization (APPI) MS and electrospray ionization (ESI) MS, along with an ultraviolet (UV) detector, corona charged aerosol detector (CAD), and an evaporative light scattering detector (ELSD), simultaneously in parallel. UV detection allowed calculation by internal standard (IS), external standard (ES), and response factor (RF) approaches, which gave values of 0.2861±0.0044, 0.2870±0.0059, and 0.2857±0.0042μg/mL, respectively, which were not statistically significantly different. This indicated an average amount of vitamin D3 of 14.5% over the label amount. APCI-MS analysis by selected ion monitoring (SIM) and two transitions of selected reaction monitoring (SRM) provided values of 0.2849±0.0055, 0.2885±0.0090, and 0.2939±0.0097μg/mL, respectively, relative to vitamin D2 as the IS. The triacylglycerol (TAG) composition was determined by APCI-MS, APPI-MS and ESI-MS, and the fatty acid (FA) compositions calculated from the TAG compositions were compared to the FA composition determined by gas chromatography (GC) with flame ionization detection (FID) of the FA methyl esters (FAME). APCI-MS provided the FA composition closest to that determined by GC-FID of the FAME. A previously reported approach to TAG response factor calculation was employed, which brought all TAG compositions into good agreement with each other, and the calculated FA compositions into excellent agreement with the FA composition determined from GC-FID of the FAME.