Search

We extend our previous work on the energetics and mechanisms of fragmentation in the mass spectrometry of triacylglycerols (TAGs). Previously, we proposed viable mechanisms for the collision-induced fragmentation of lithiated tripropionylglycerol using triple-quadrupole mass spectrometry. In this work, we used a QqLIT mass spectrometer to study both double- and triple-stage spectra from a range of TAGs having acid chains of types AAA (identical acid chains), AAB, ABA, and ABC, with chain lengths of 6-18 carbon atoms; we also studied some TAGs having a single double bond in the Δ-9 position. Detailed computations on fragmentation pathways were carried out on lithiated trihexanoylglycerol and on a limited number of longer chain ions. Second-stage fragmentations led to the formation of a lithiated ion after the loss of a neutral acid. With a further input of energy, this ion could rearrange into two other ions, one being formed more easily than the other. In a triple-stage fragmentation, these three ions give a defined series of product ions, some of which are characteristic of the substitution pattern on the glycerol core of the TAG. Computed reaction energies for product ion formation showed comparable trends to the relative intensities of the observed product ion spectra. These results have enabled us to propose unified mechanisms for the double- and triple-stage fragmentation of lithiated TAGs. The mechanisms have reasonable energetics, and all ions, as well as saddle points, have viable geometries. In addition, the fragmentation mechanisms are in accord with all the published experimental mass spectra.

Many methods, often depending on tandem mass spectrometry, have been developed for analysis of complex mixtures of triacylglycerols (TAGs), especially in clinical diagnostics and food authentication. Understanding the fragmentation mechanisms of cationized TAGs has proved problematic. To obtain a better understanding of viable mechanisms, detailed studies including double- and triple-stage tandem mass spectrometry were made using electrospray ionization on lithiated and sodiated tripropanoyl- and trihexanoylglycerols. Density functional theory computations, including a functional parameterized for van der Waals interactions, were used to correlate computed energies with mass spectra. Losses of both a neutral salt and a neutral acid corresponding to a glycerol side chain were observed as major product ions in MS 2 experiments. Signal intensities at low collision energies correlated well with computed energies. However, an important difference between the lithiated and sodiated ions was the appearance of the sodium cation as a major fragmentation product. Computations on the product ions resulting from the loss of a neutral acid indicated multiple structures for the lithiated ions but mainly a single structure for the sodiated ions. The lithiated product ions could be fragmented further (pseudo-MS 3 ) to give additional structural information, whereas the sodiated ions gave only m/z 23. The longer chain TAG, while giving a much less intense mass spectrum than the shorter chain TAG, gave comparable MS 2 and MS 3 product ion spectra. Taken together, the spectral and computational work described herein offer a new and detailed pathway for collision-induced fragmentation of lithiated and sodiated saturated TAGs.

Analysis of triacylglycerols (TAGs), found as complex mixtures in living organisms, is typically accomplished using liquid chromatography, often coupled to mass spectrometry. TAGs, weak bases not protonated using electrospray ionization, are usually ionized by adduct formation with a cation, including those present in the solvent (e.g., Na(+)). There are relatively few reports on the binding of TAGs with cations or on the mechanisms by which cationized TAGs fragment. This work examines binding efficiencies, determined by mass spectrometry and computations, for the complexation of TAGs to a range of cations (Na(+), Li(+), K(+), Ag(+), NH4(+)). While most cations bind to oxygen, Ag(+) binding to unsaturation in the acid side chains is significant. The importance of dimer formation, [2TAG + M](+) was demonstrated using several different types of mass spectrometers. From breakdown curves, it became apparent that two or three acid side chains must be attached to glycerol for strong cationization. Possible mechanisms for fragmentation of lithiated TAGs were modeled by computations on tripropionylglycerol. Viable pathways were found for losses of neutral acids and lithium salts of acids from different positions on the glycerol moiety. Novel lactone structures were proposed for the loss of a neutral acid from one position of the glycerol moiety. These were studied further using triple-stage mass spectrometry (MS(3)). These lactones can account for all the major product ions in the MS(3) spectra in both this work and the literature, which should allow for new insights into the challenging analytical methods needed for naturally occurring TAGs.

Reversed-phase high performance liquid chromatography (RP-HPLC), followed by post-column addition of lithium salts and electrospray ionisation triple-stage mass spectrometry (ESI-MS(3)) of lithiated TAG adducts, is shown to provide a useful method for the positional analysis of triacylglycerols (TAGs) in fish oils containing eicosapentaenoic (EPA, 20:5) and docosahexaenoic acids (DHA, 22:6). One prominent fragmentation pathway in the ESI-MS(3) of these adduct ions involves the loss of a fatty acid from the sn-1/3 position in the first step followed by the loss of an α,β-unsaturated fatty acid from the sn-2 position in the second. Regioisomeric TAGs of the type ABA and AAB produced abundant product ions - [ABA+Li-RACOOH-R'BCHCHCOOH](+) and [AAB+Li-RACOOH-R'ACHCHCOOH](+) - the relative intensities of which were dependent on the position of acyl substituents. Standard solutions of TAGs containing different ratios of the regioisomeric pairs MME/MEM, PPE/PEP, PPD/PDP, EEP/EPE and DDP/DPD (M=14:0, P=16:0, E=20:5, D=22:6) were analysed by ESI-MS(3) with a quadrupole linear ion trap instrument. Methodology developed on the standards was applied to quantifying the relative isomeric abundances of EPA and DHA in several fish oil samples. DHA was preferentially located at the sn-2 position in both DHA-containing TAGs studied, while EPA was either observed at near equal levels in all positions, or predominantly at the sn-1 and -3 positions in some cases. The analysis protocol allows for quantification of the designated regioisomers in one simple, rapid chromatographic procedure using a single column and has the advantage of specificity over other methods for the positional analysis of TAGs, since it eliminates interferences associated with co-eluting TAGs of the same molecular weight that yield isobaric diacylglycerol-like product ions., (Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.)

Rationale: Regioisomeric analysis of triacylglycerols is important in understanding lipid biochemistry and the involvement of lipids in disease and nutrition. The use of calibration plots employing fractional abundances provides a simple and rapid method for such analyses. These plots are believed to be linear, but evidence exists for non-linearity. The behavior of such plots needs to be understood to allow for proper interpretation of regioisomeric data., Methods: Solutions of five regioisomer pairs were prepared from pure standards and used to construct calibration plots using triple-stage tandem mass spectrometry (MS(3) ) with electrospray ionization (ESIMS(3) ) and cationization by lithium ions. The data were taken by direct infusion with an AB SCIEX QTRAP 2000 QqLIT mass spectrometer., Results: Non-linear calibration plots were observed for the four isomer pairs containing the polyunsaturated eicosapentaenoic (20:5) and docosahexaenoic (22:6) acids paired with palmitic acid (16:0) or myristic acid (14:0), while the pair including palmitic and stearic (18:0) acids provided a linear plot. A non-linear model was developed for these plots and then verified experimentally., Conclusions: The fractional abundance calibration plots used in regioisomeric analysis of triacylglycerols are intrinsically non-linear, but may appear linear if the scatter in data points obscures the curvature, if the curvature is slight, or if the response factors for the two isomers in the regioisomer pair are similar. Therefore, linearity should not be assumed for these types of measurements until confirmed experimentally., (Copyright © 2013 John Wiley & Sons, Ltd.)

Polycyclic aromatic sulfur-containing compounds (PASHs) are commonly found in fossil fuels and are of considerable importance in environmental studies. This work presents detailed studies on the fragmentation patterns of radical cations formed from four representative PASHs, benzo[b]thiophene, dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene, using tandem atmospheric pressure chemical ionization mass spectrometry (APCI-MS/MS). Understanding these fragmentation patterns can be a useful aid in the analysis of PASHs employing APCI or electron ionization (EI-MS/MS), either alone or in conjunction with liquid or gas chromatography., (John Wiley & Sons, Ltd)

The behavior in atmospheric pressure chemical ionization of selected model polycyclic aromatic compounds, pyrene, dibenzothiophene, carbazole, and fluorenone, was studied in the solvents acetonitrile, methanol, and toluene. Relative ionization efficiency and sensitivity were highest in toluene and lowest in methanol, a mixture of molecular ions and protonated molecules was observed in most instances, and interferences between analytes were detected at higher concentrations. Such interferences were assumed to be caused by a competition among analyte molecules for a limited number of reagent ions in the plasma. The presence of both molecular ions and protonated analyte molecules can be attributed to charge-transfer from solvent radical cations and proton transfer from protonated solvent molecules, respectively. The order of ionization efficiency could be explained by incorporating the effect of solvation in the ionization reactions. Thermodynamic data, both experimental and calculated theoretically, are presented to support the proposed ionization mechanisms. The analytical implications of the results are that using acetonitrile (compared with methanol) as solvent will provide better sensitivity with fewer interferences (at low concentrations), except for analytes having high gas-phase basicities.

Software, available at no cost on the Internet, is described which uses polynomial expansion algorithms to calculate the isotope patterns for precursor ion, neutral loss, and MSn product ion tandem mass spectra. Such information is useful for determining product ion and neutral loss composition, identification of analytes in complex samples, deconvolution of overlapping spectra, and correction of peak heights or areas in quantitative analysis. The effect of less than unit mass resolution on the isotope patterns is described and experimental examples of the use of the software are presented.

Palytoxin (PlTX) is one of the most toxic non-protein molecules extracted from soft corals, posing significant risks within the food chain. To mitigate these risks, regulatory agencies prioritize developing reliable analytical techniques for monitoring and risk management of PlTX in marine organisms. The analysis of PlTX using liquid chromatography-tandem mass spectrometry (LC/MS/MS) has become a preferred method due to its high sensitivity and specificity. However, previous studies have reported challenges in achieving sharp peak shapes and adequate resolution in PlTX detection, which can compromise the accuracy and reliability of quantification. Therefore, PlTX monitoring is actively performed using an emerging and enhanced LC/MS/MS method. To ensure accurate quantification of PlTX, which is present in trace amounts in marine organisms, it is essential to optimize chromatographic separation and ionization. In this study, we optimized the separation conditions to improve PlTX quantification through the adjustment of a buffer system, specifically increasing the concentration of ammonium formate using reverse-phase liquid chromatography coupled with multiple reaction-monitoring mass spectrometry (RPLC/MRM-MS). This optimization significantly improved peak sharpness and resolution, enhancing the overall analytical performance of LC–MS/MS for PlTX detection in marine samples. Our findings suggest that the optimized method can serve as a reliable reference for developing standardized protocols aimed at improving PlTX analysis. [ABSTRACT FROM AUTHOR]

Detailed studies have been made using different source gases and solvents in a Micromass Quattro mass spectrometer under positive ion atmospheric pressure chemical ionization conditions. The major background ions from nitrogen, air, or carbon dioxide were investigated by tandem mass spectrometry, followed by similar studies on solvents commonly employed in normal- and reversed-phase high-performance liquid chromatography, namely, water-acetonitrile, acetonitrile, and dichloromethane, with nitrogen, air, or carbon dioxide; hydrocarbon solvents were studied using nitrogen. Spectra were interpreted in terms of the gases, solvents, and their impurities. The acetonitrile spectra provided clear evidence for both charge exchange and proton transfer, the former being facilitated by the introduction of some air into a flow of nitrogen. Radical cations of acetonitrile dimers, trimers, and tetramers were observed, as were protonated dimer and trimer species. Examination of the analytical response of four polycyclic aromatic hydrocarbons in various hydrocarbon solvents, with nitrogen gas, showed that the sensitivity of detection for an analyte and its ionization mechanism are dependent on both the analyte structure and the solvent, with pyrene showing the highest sensitivity, phenanthrene and fluorene being intermediate, and naphthalene having the lowest sensitivity. The degree of protonation followed the same trend. Signal intensity and degree of protonation were dependent on the alkane solvent used, with isooctane providing the best overall sensitivity for the sum of protonated molecules and molecular ions. The ions observed in these studies appeared to be the most stable ions formed under equilibrium conditions in the source.

The response of atmospheric pressure chemical ionization (APCI) mass spectrometry to selected polycyclic aromatic compounds (PACs) was examined in a Micromass Quattro atmospheric pressure ion source as a function of both solvents and source gases. Typical PACs found in petroleum samples were represented by mixtures of naphthalene, fluorene, phenanthrene, pyrene, fluoranthene, chrysene, triphenylene, perylene, carbazole, dibenzothiophene, and 9-phenanthrol. A large range of different gases in the APCI source was studied, with emphasis on nitrogen, air, and carbon dioxide. Solvents used included water-acetonitrile, acetonitrile, dichloromethane, and hexanes. The signal responses were dependent on both the gases and solvents used, as was the ionization mechanism, as indicated by the degree of protonation with respect to the level of charge exchange. The combination of carbon dioxide in the nebulizer gas stream with nitrogen in the other streams gave a three- to fourfold better sensitivity than using nitrogen alone for both test mixtures and for complex samples.

Analysis of triacylglycerol (TG) and phospholipid sn-positional isomers can be divided into two main categories: (a) direct separation by chromatography or other means such as ion mobility mass spectrometry and (b) quantification of regioisomer ratios by structurally informative fragment ions with mass spectrometric methods. Due to long retention times and limited performance, researchers are moving away from direct chromatographic separation of isomers, using mass spectrometry instead. Many established analytical methods are targeting specific isomers of interest instead of untargeted analysis of comprehensive profiles of regioisomers. Challenges remain arising from the large number of isobaric and isomeric lipid species in natural samples, often overlapping chromatographically and sharing structurally informative fragment ions. Further, fragmentation of glycerolipids is influenced by the nature of the attached fatty acids, and the lack of available regiopure standards is still an obstacle for establishing calibration curves required for accurate quantification of regioisomers. Additionally, throughput of many methods is still quite limited. Optimization algorithms and fragmentation models are useful especially for analysis of TG regioisomers, as identification using calibration curves alone without proper separation is difficult with complex samples., (© 2023 The Authors. Mass Spectrometry Reviews published by John Wiley & Sons Ltd.)

Thlaspi arvense (Pennycress) is an emerging feedstock for biofuel production because of its high seed oil content enriched in erucic acid. A transcriptomic and a lipidomic study were performed to analyze the dynamics of gene expression, glycerolipid content and acyl-group distribution during seed maturation. Genes involved in fatty acid biosynthesis were expressed at the early stages of seed maturation. Genes encoding enzymes of the Kennedy pathway like diacylglycerol acyltransferase1 (TaDGATl), lysophosphatidic acid acyltransferase (TaLPAT) or glycerol 3-phosphate acyltransferase (TaGPAT) increased their expression with maturation, coinciding with the increase in triacylglycerol species containing 22:1. Positional analysis showed that the most abundant triacylglycerol species contained 18:2 at sn-2 position in all maturation stages, suggesting no specificity of the lysophosphatidic acid acyltransferase for very long chain fatty acids. Diacylglycerol acyltransferase2 (TaDGAT2) mRNA was more abundant at the initial maturation stages, coincident with the rapid incorporation of 22:1 to triacylglycerol, suggesting a coordination between Diacylglycerol acyltransferase enzymes for triacylglycerol biosynthesis. Genes encoding the phospholipid-diacylglycerol acyltransferase (TaPDAT1), lysophosphatidylcholine acyltransferase (TaLPCAT) or phosphatidylcholine diacylglycerolcholine phosphotransferase (TaPDCT), involved in acyl-editing or phosphatidyl-choline (PC)-derived diacylglycerol (DAG) biosynthesis showed also higher expression at the early maturation stages, coinciding with a higher proportion of triacylglycerol containing C18 fatty acids. These results suggested a higher contribution of these two pathways at the early stages of seed maturation. Lipidomic analysis of the content and acyl-group distribution of diacylglycerol and phosphatidyl-choline pools was compatible with the acyl content in triacylglycerol at the different maturation stages. Our data point to a model in which a strong temporal coordination between pathways and isoforms in each pathway, both at the expression and acyl-group incorporation, contribute to high erucic triacylglycerol accumulation in Pennycress. [ABSTRACT FROM AUTHOR]

Online monitoring of dynamic chemical processes involving a wide volatility range of hydrocarbon species is challenging due to long chromatographic measurement times. Mass spectrometry (MS) overcomes chromatographic delays. However, the analysis of n-alkane mixtures by MS is difficult because many fragment ions are formed, which leads to overlapping signals of the homologous series. Atmospheric pressure chemical ionization (APCI) is suitable for the analysis of saturated hydrocarbons and is the subject of current research. Still, although APCI is a "soft ionization" technique, fragmentation is typically inevitable. Moreover, it is usually applied for liquid samples, while an application for online gas-phase monitoring is widely unexplored. Here, we present an automated APCI-MS method for an online gas-phase analysis of volatile and semi-volatile n-alkanes. Mass spectra for n-heptane and n-decane reveal [M-H]+, [M-3H]+ and [M-3H+H2O]+ as abundant ions. While [M-H]+ and [M-3H]+ show an excessive fragmentation pattern to smaller CnH2n+1+ and CnH2n-1+ cations, [M-3H+H2O]+ is the only relevant signal within the CnH2n+1O+ ion group, i.e., no chain cleavage is observed. This makes [M-3H+H2O]+ an analyte-specific ion that is suitable for the quantification of n-alkane mixtures. A calibration confirms the linearity of C7 and C10 signals up to concentrations of ~1000–1500 ppm. Moreover, validated concentration profiles are measured for a binary C7/C10 mixture and a five-alkane C7/C10/C12/C14/C20 mixture. Compared to the 40-min sampling interval of the reference gas chromatograph, MS sampling is performed within 5 min and allows dynamic changes to be monitored. [ABSTRACT FROM AUTHOR]

Natural abundance and isotopically labelled tryptic peptides are routinely employed as standards in quantitative proteomics. The certification of the peptide content is usually carried out by amino acid analysis using isotope dilution mass spectrometry (IDMS) after the acid hydrolysis of the peptide. For the validation and traceability of the amino acid analysis procedure, expensive certified peptides must be employed. In this work we evaluate different IDMS alternatives which will reduce the amount of certified peptide required for validation of the amino acid analysis procedure. In this context, the characterization of both natural and isotopically labelled synthetic angiotensin I peptides was carried out. First, we applied a fast procedure for peptide hydrolysis based on microwave-assisted digestion and employed two certified peptide reference materials SRM 998 angiotensin I and CRM 6901-b C-peptide for validation of the hydrolysis procedure. The amino acids proline, leucine, isoleucine, valine, tyrosine, arginine and phenylalanine were evaluated for their suitability for peptide certification by IDMS by both liquid chromatography with tandem mass spectrometry (LC–MS/MS) and gas chromatography with mass spectrometry (GC)–MS/MS. Then, natural angiotensin I and 13C1-labelled angiotensin I were synthesized in-house and purified by preparative liquid chromatography. The concentration of the 13C1-labelled angiotensin I peptide was established by reverse IDMS in its native form using SRM 998 angiotensin I as reference. The concentration of the natural synthesized peptide was determined by IDMS both using the 13C1-labelled peptide in its native form and by amino acid analysis showing comparable results. Finally, the synthetic naturally abundant angiotensin I peptide was employed as "in-house" standard for the validation of subsequent peptide characterization procedures. Therefore, the novelty of this work relies on, first, the development of a faster hydrolysis procedure assisted by focused microwaves, providing complete hydrolysis in 150 min, and secondly, a validation strategy combining GC–MS and LC–MS/MS that allowed us to certify the purity of an in-house-synthesized peptide standard that can be employed as quality control in further experiments. [ABSTRACT FROM AUTHOR]

Soil is a vital component of the ecosystem that drives the holistic homeostasis of the environment. Directly, soil quality and health by means of sufficient levels of soil nutrients are required for sustainable agricultural practices for ideal crop yield. Among these groups of nutrients, soil carbon is a factor which has a dominating effect on greenhouse carbon phenomena and thereby the climate change rate and its influence on the planet. It influences the fertility of soil and other conditions like enriched nutrient cycling and water retention that forms the basis for modern 'regenerative agriculture'. Implementation of soil sensors would be fundamentally beneficial to characterize the soil parameters in a local as well as global environmental impact standpoint, and electrochemistry as a transduction mode is very apt due to its feasibility and ease of applicability. Organic Matter present in soil (SOM) changes the electroanalytical behavior of moieties present that are carbon-derived. Hence, an electrochemical-based 'bottom-up' approach is evaluated in this study to track soil organic carbon (SOC). As part of this setup, soil as a solid-phase electrolyte as in a standard electrochemical cell and electrode probes functionalized with correlated ionic species on top of the metalized electrodes are utilized. The surficial interface is biased using a square pulsed charge, thereby studying the effect of the polar current as a function of the SOC profile. The sensor formulation composite used is such that materials have higher capacity to interact with organic carbon pools in soil. The proposed sensor platform is then compared against the standard combustion method for SOC analysis and its merit is evaluated as a potential in situ, on-demand electrochemical soil analysis platform. [ABSTRACT FROM AUTHOR]

Abstract—The kinetic laws of Fe3+ ion electroreduction in the KCl–NaCl–CsCl eutectic melt at 823 K are determined. The potentials of metallic iron and dysprosium formation on the inert tungsten electrode in the KCl–NaCl–CsCl molten system are found to differ by approximately 1.5 V. In the case of the combined presence of Fe3+ and Dy3+ ions in the KCl–NaCl–CsCl eutectic melt, a certain depolarization of dysprosium ion electroreduction occurs on the metallic iron preliminary deposited at the tungsten electrode to form iron- and dysprosium-based intermetallic phases of different compositions. The dissolution potentials of the different intermetallic phases DyxFey are determined by open circuit chronopotentiometry. [ABSTRACT FROM AUTHOR]

Four new tremulane sesquiterpenes, named phaeosphaerienols A-D (1-4), and two new pyroglutamate-containing dipeptides, named phaeosphaeratides A-B (5-6), were isolated from the mangrove endophytic fungus Phaeosphaeriopsis sp. P11, together with a new 2-furancarboxylic acid derivative (7). Structurally, pheaosphaerienols A-C (1-3) are rare tremulanes containing a 1,10-epoxide moiety. The structures of these compounds were established by extensive NMR spectroscopic data, single-crystal X-ray diffraction analysis, and Marfey's derivatization method. All the isolates were evaluated for their cytotoxic, antibacterial, and DPPH free radical scavenging effects. However, none of the compounds exhibited obvious activities., (© 2024 Wiley-VHCA AG, Zurich, Switzerland.)

There has been an increased interest in the development of green analytical methods for polycyclic aromatic hydrocarbons in environmental samples due to their toxicity and ubiquitous nature. In this work, the feasibility of on-line supercritical fluid extraction-supercritical fluid chromatography-tandem mass spectrometry was investigated for rapid and automated determination of the 16 United States Environmental Protection Agency priority polycyclic aromatic hydrocarbons in particulate matter samples. Three specialty polycyclic aromatic hydrocarbons columns with different stationary phases were screened and an octadecyl-silica column was selected for method development. Enhanced extraction efficiency was achieved using an extraction program with gradient flow rate and gradient concentration of acetonitrile as a modifier. The method was evaluated by analyzing standard reference materials of urban dust and diesel particulate matter from the National Institute of Standards and Technologies. Possible reasons for the unsatisfactory recoveries with certain polycyclic aromatic hydrocarbons are discussed., (© 2021 Wiley-VCH GmbH.)

Supercritical fluid chromatography (SFC) is a promising alternative to conventional chromatographic methods and has several advantages over them in selectivity, efficiency, speed of separation, and environmental friendliness. Its combination with atmospheric pressure chemical ionization (APCI) mass spectrometric detection is one of the central areas of method development and requires an understanding of the APCI specificity in using carbon dioxide-based mobile phases. In the present study, the composition of negatively charged ions formed under APCI conditions for carbon dioxide–organic modifier (methanol, isopropanol, acetonitrile) systems, and also the influence of the mobile phase and ion source parameters (corona discharge needle voltage, temperature) on it are studied using high-resolution mass spectrometry. The results obtained testify to a significant role of carbon dioxide as a direct precursor for the formation of reaction particles (hydrocarbonate and percarbonate anions, carbonate radical anion) and as a reagent capable of shifting the ion-molecular equilibrium in corona discharge plasma and forming compounds with the organic modifier (alkylcarbonic acid anions in the case of alcohols, adduct with a deprotonated acetonitrile molecule). Ion-molecular equilibria involving carbon dioxide result in the formation of a large number of reactive particles that can take part in the ionization processes of analytes in SFC–APCI-MS. [ABSTRACT FROM AUTHOR]

Dinitrotoluenes (DNTs) and nitrotoluenes (NTs) are found in the environment as metabolites of trinitrotoluene (TNT). When acetone is used as the solvent/eluent in atmospheric pressure chemical ionization‐mass spectrometry (APCI‐MS), the reactant ion is [2Acetone + O2]•− for the negative ion mode. The reactant ion reacts with an analyte to produce M•− and/or [M – H]− under atmospheric pressure. In this study, ionization behaviors of NT (2‐, 3‐, and 4‐NTs) and DNT isomers (2,3‐, 2,4‐, and 2,6‐DNTs) by reactions with [2Acetone + O2]•− were investigated. The energy‐minimized structures of the product ions and their energies were calculated to explain the differences in the ionization behaviors. Typical NT‐ and DNT‐related ions were produced by reactions with [2Acetone + O2]•−; NT•−, [NT – H]−, DNT•−, [DNT – H]−, and [DNT – NO]− ions. The ionization efficiencies of NT‐ and DNT‐related ions increased by increasing the source fragmentor voltage, and those of DNT‐related ions were higher than those of the NT‐related ions owing to the presence of an additional nitro group. The ionization efficiency of 3‐NT•− was higher than that of [NT – H]−, while that of [DNT – H]− was higher than those of DNT•− and [DNT – NO]−. The ionization efficiency order of NT•− was 3‐NT > 4‐NT > 2‐NT, while that of [DNT – H]− was 2,4‐DNT > 2,6‐DNT > 2,3‐DNT. The [NT – H]− and [DNT – H]− ions were stabilized by resonance structures containing nitro groups. The [DNT – NO]− ions were formed through the transition state. [ABSTRACT FROM AUTHOR]

An instrumental neutron activation analysis method in conjunction with Compton suppression spectrometry was developed for the simultaneous determination of nanogram levels of Cl, Br and I in salmon muscle and skin. Several non-chlorinated solvent systems were evaluated for the extraction of lipids containing organohalogens and an acetone-hexane (1:1) system was selected because it gave the highest extraction efficiency with least contamination. An extensive quality assurance program was designed. Lipid fractionation procedures were developed using size exclusion, solid phase extraction and thin layer chromatography followed by characterization using 1H, 13C and 31P nuclear magnetic resonance and mass spectrometry. Results show that both muscle and skin had high levels of triacylglycerols. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of acetonitrile to ethylamine with a high selectivity is a novel approach to manufacture valuable primary amines which are important raw material in organic chemical industry. However, the poor ethylamine Faradic efficiency (FEethylamine) and catalyst stability at the high current density prohibit this method from being practically used. Herein, CuNi alloy ultrafine-nano-particles based on the d-orbital coupling modulation were synthesized through the electrodeposition and their catalytic performance towards acetonitrile reduction reaction (ACNRR) has been systematically studied. The highest FEethylamine (97%) is achieved with the current density of −114 mA cm−2. For practical application, the current density can reach −602.8 mA cm−2 with 82.8% FEethylamine maintained. With the appearance of other organics which co-exist with acetonitrile in the SOHIO process, CuNi can also hydrogenate acetonitrile in it with more than 80% FEethylamine. Our in-situ spectroscopy analysis and DFT calculations towards the acetonitrile hydrogenation behavior reveal that the evenly dispersed Ni in Cu modulates the d-band so as to endow CuNi with the better acetonitrile adsorption, milder binding energy with the reaction intermediates, smaller barrier for *CH3CH2NH2 desorption and higher ability for H2O dissociation to provide *H. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of dysprosium ions, as well as dysprosium and nickel ion co-reduction, on inert tungsten electrodes and active nickel electrodes were studied in the eutectic KCl-NaCl-CsCl melt at a temperature of 823 K using the methods of cyclic and square-wave voltammetry and open circuit chronopotentiometry. The process of Dy3+ ions electroreduction was found to be reversible and to proceed within a single three-electron stage up to the polarization rate of 0.1 V/s. The increase in the polarization rate indicates a slower rate of the charge transfer, which causes the quasi-reversible character of the charge transfer. It is shown that when the KCl-NaCl-CsCl eutectic melt contains both nickel and dysprosium ions, the voltammetry curves at 823 K have a wave of nickel ion reduction at the potentials of −(0.22–0.28) V and a dysprosium ion reduction at the potentials of −(2.175–2.250) V relative to a chlorine-silver reference electrode. Apart from these waves, the voltammograms have two reduction waves at the potentials of −(1.9–1.95) V and −(2.05–2.1) V. These waves are associated with the reduction of dysprosium ions and their depolarization on metallic nickel, which was preliminary deposited on the tungsten electrode, as well as the formation of the intermetallic phases of dysprosium and nickel of various DyxNiy compositions. The (E-t) dependencies of the open circuit chronopotentiometry elucidate plateaus of the potential delay, which correspond to the dissolution of separate dysprosium and nickel intermetallic phases. Based on the results of the voltammetry changes and the chronopotentiometry of the open circuit, a series of electrochemical syntheses were performed in the potentiostatic regime at the potentials of −(1.7–2.1) V. The intermetallic phases of DyNi5, DyNi3 and DyNi2 were obtained at a definite ratio of the dysprosium and nickel chloride concentrations in the KCl-NaCl-CsCl eutectic melt and at a temperature of 823 K. The synthesized intermetallic samples were characterized by X-ray diffraction and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

An interface for coupling a laser Raman spectrometer employing photon counting detection to an on-line programmable calculator or minicomputer is described. The resulting system provides both background and spectral data in digital form that allows data manipulation to be easily performed. In addition online computer control allows the enhancement of the signal-to-noise ratio by signal averaging. The spectrum of gaseous N(2) and O(2) taken with the system illustrates the capability of the interface and computer when coupled with the spectrometer to make precise and sensitive measurements.

Electrochemical methods have been widely applied to measure fundamental data of element ions in molten salts. However, most applications neglected the fundamental premises and assumptions, which could lead to inaccurate results. This study provides a critical review on the methods and examines the limitation of each method in molten salt systems. The important parameters discussed in this work include electron transfer number, diffusion coefficient, formal potential, exchange current density, and charge transfer coefficient. Furthermore, the study discusses good practices to improve and proper applications to obtain accurate data. [ABSTRACT FROM AUTHOR]

This Tutorial is to provide a summary of parameters useful for successful outcomes of laserspray ionization (LSI) and related methods that employ a laser to ablate a matrix:analyte sample to produce highly charged ions. In these methods the purpose of the laser is to transfer matrix‐analyte clusters into the gas phase. Ions are hypothesized to be produced by a thermal process where emitted matrix:analyte gas‐phase particles/clusters are charged and loss of matrix from the charged particles leads to release of the analyte ions into the gas phase. The thermal energy responsible for the charge‐separation process is relatively low and not necessarily supplied by the laser; a heated inlet tube linking atmospheric pressure with the first vacuum stage of a mass spectrometer is sufficient. The inlet becomes the "ion source", and inter alia, pressure, temperature, and the matrix, which can be a solid, liquid, or combinations, become critical parameters. Injecting matrix:analyte into a heated inlet tube using laser ablation, a shockwave, or simply tapping, all produce the similar mass spectra. Applications are provided that showcase new opportunities in the field of mass spectrometry. [ABSTRACT FROM AUTHOR]

Surfactants are surface‐active agents widely used in numerous applications in our daily lives as personal care products, domestic, and industrial detergents. To determine complex mixtures of surfactants and their degradation products, unselective and rather insensitive methods, based on colorimetric and complexometric analyses are no longer employable. Analytical methodologies able to determine low concentration levels of surfactants and closely related compounds in complex matrices are required. The recent introduction of robust, sensitive, and selective mass spectrometry (MS) techniques has led to the rapid expansion of the surfactant research field including complex mixtures of isomers, oligomers, and homologues of surfactants as well as their chemically and biodegradation products at trace levels. In this review, emphasis is given to the state‐of‐the‐art MS‐based analysis of surfactants and their degradation products with an overview of the current research landscape from traditional methods involving hyphenate techniques (gas chromatography‐MS and liquid chromatography‐MS) to the most innovative approaches, based on high‐resolution MS. Finally, we outline a detailed explanation on the utilization of MS for mechanistic purposes, such as the study of micelle formation in different solvents. [ABSTRACT FROM AUTHOR]

Abstract—The electrochemical behavior of neodymium ions and their combined electroreduction with nickel ions at inert tungsten and active nickel electrodes are studied in the KCl–NaCl–CsCl eutectic melt at 823 K using cyclic voltammetry, square-wave voltammetry, chronopotentiometry, and open-circuit chronopotentiometry. The electroreduction of Nd3+ ions occurs reversibly in one three-electron step at polarization rates lower than 0.1 V/s. An increase in the polarization rate makes it possible to reveal that the charge-transfer step is retarded and becomes quasi-reversible. In the presence of both neodymium and nickel ions in the KCl–NaCl–CsCl eutectic melt at 823 K, voltammetry dependences show a nickel ion reduction wave at potentials from –0.18 to –0.23 V and a neodymium ion reduction wave at potentials from –2.16 to –2.22 V vs. silver chloride reference electrode. In addition to these waves, voltammograms have three reduction waves at potentials from –1.65 to –1.75 V, from –1.95 to –2.0 V, and from –2.07 to –2.12 V. These waves appear due to the combined electroreduction of neodymium and nickel ions on metallic nickel preliminary deposited on the tungsten electrode with a certain depolarization and formation of intermetallic phases of neodymium and nickel of various compositions (NdxNiy). Open-circuit chronopotentiometry dependences reveal a potential delay plateau corresponding to the dissolution of individual phases of neodymium and nickel intermetallic compounds. A series of electrochemical syntheses have been conducted in the potentiostatic mode at potentials from –1.8 to –2.2 V on the basis of the results of voltammetry measurements and open-circuit chronopotentiometry. At a certain ratio of concentrations of neodymium and nickel chlorides in the KCl–NaCl–CsCl eutectic melt at 823 K, the intermetallic phases NdNi5, NdNi3, and NdNi2 are formed. The synthesized samples of neodymium and nickel intermetallic compounds are characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy. The emf values of the NdxNiy intermetallic compounds are measured in the two-phase coexisting states at 823 K. The relative partial molar free Gibbs energy and the activity of neodymium in the NdxNiy intermetallic compounds are calculated from the determined values of emf. [ABSTRACT FROM AUTHOR]