Reactions Of Negative Ions Research Articles

A SIFT Study of Reactions of Positive and Negative Ions With Polyfluoroalkyl (PFAS) Molecules in Dry and Humid Nitrogen at 393 K.

Data are required for SIFT-MS analysis of perfluoroalkyl and polyfluoroalkyl substances (PFAS), which are persistent in the environment and cause adverse health effects. Specifically, the rate coefficients and product ion branching ratios of the reactions of H3O+, NO+, O2 +•, O-•, OH-, O2 -•, NO2 - and NO3 - with PFAS vapours are needed. The dual polarity SIFT-MS instrument (Voice200) was used to generate these eight reagent ions and inject them into the flow tube with N2 carrier gas at a temperature of 393 K. Vapours of pentafluoropropionic acid, heptafluorobutyric acid, nonafluoro-1-hexanol, perfluoro-2-methyl-2-pentene, perfluorohexanoic acid, perfluoro(2-methyl-3-oxahexanoic) acid, tridecafluoro-1-octanol and nonafluorobutane-1-sulfonic acid were introduced in dry and humid air. Full-scan mass spectra were collected for all reagents at variable PFAS concentrations and analysed numerically. Rate coefficients were determined for 64 reactions, for which 55 positive and 71 negative product ions were identified. The branching ratios for the primary reaction channels were extracted from the data, and the secondary chemistry with H2O molecules was qualitatively assessed. The thermochemical data were calculated for the H3O+ reactions using density functional theory (DFT). An important observation is that secondary reactions with water molecules remove the positive product ions, making them unsuitable for practical SIFT-MS analysis of PFAS vapours. In contrast, most negative reaction product ions are not significantly affected by humidity and are thus preferred for the SIFT-MS analyses of PFAS substances in various gaseous matrices.

Chemical ionization of carboxylic acids and esters in negative mode selected ion flow tube – Mass spectrometry (SIFT-MS)

Chemical ionization of carboxylic acids and esters in negative mode selected ion flow tube – Mass spectrometry (SIFT-MS)

Development and validation of a bioanalytical method of analyzing 3′- and 6′-sialyllactose using liquid chromatography–tandem mass spectrometry in minipig plasma and its application in a pharmacokinetic study

Development and validation of a bioanalytical method of analyzing 3′- and 6′-sialyllactose using liquid chromatography–tandem mass spectrometry in minipig plasma and its application in a pharmacokinetic study

Experimental observation of the effect of electron attachment and detachment reactions on the electron energy distribution in an inductive oxygen discharge

Electron energy distribution functions (EEDFs) are measured with varying radio-frequency (RF) power in an oxygen inductive discharge. At a pressure of 10 mTorr, the EEDF has a Maxwellian distribution, and the low-energy (1–5 eV) electron temperature, Te,low, monotonically decreases with RF power. However, at a pressure of 100 mTorr, Te,low increases at low RF power (80–150 W) and decreases at high RF power (150–300 W), and the EEDF has a Druyvesteyn-like distribution. These changes in Te,low are attributed to electron attachment and detachment reactions, which are the main creation and loss reactions of negative ions. To investigate this relationship between Te,low and collisional reactions, the reaction coefficients of several reactions are calculated, and the electronegativity (α) is measured with varying RF power. The EEDF is modified by electron attachment and detachment reactions, which lead to a change in Te,low; this modification of EEDF is supported by calculated reaction coefficients and measured α.

Multiple dehydrogenation reactions of negative ions in low pressure silane plasma chemistry

Micro-particle formation in low pressure silane (SiH4) plasmas has been of technical interest and concern for at least 40 years. Negative ion plasma chemistry is a candidate for the initial nucleation, which has been extensively studied both experimentally and theoretically. Nevertheless, the nature and mechanisms of anion-neutral reactions remain uncertain in models of nucleation. In the pure silane, 0.1 mbar plasma of this work, silicon hydride anion mass spectra are interpreted in terms of iterative anion–silane reactions, involving release of one, or two, hydrogen molecules. Such ‘multiple dehydrogenation’ has been directly observed by Operti et al [2006 Rapid Commun. Mass Spectrom. 20 2696], where triple dehydrogenation also occurred. A statistical model, defined uniquely by a branching ratio of 68% for single hydrogenation, and 32% for double dehydrogenation, gives an accurate fit to the hydrogen distribution for all heavy silicon hydride anions (abbreviated here by ‘silanions’), up to at least 800 atomic mass units. Most theoretical models of silanion-neutral nucleation consider dehydrogenation where no more than one H2 molecule is released. It is suggested that multiple dehydrogenation could improve the comparison of theory with experiments.

Negative ion relaxation and reactions in a cryogenic storage ring

An overview of recent experimental results of studies of negative atomic and molecular ions in the Double ElectroStatic Ion-Ring ExpEriment, DESIREE is given. Metastable level lifetimes in atomic negative ions have been measured by time-dependent laser photodetachment. Rotational relaxation of diatomic anions is studied by near-threshold photodetachment. Spontaneous decays of small metal cluster anions by electron emission and fragmentation is studied with decay-channel specificity. Finally, mutual neutralisation of pairs of negative and positive ions has been investigated with initial and final state selectivity.

Direct analysis of aldehydes and carboxylic acids in the gas phase by negative ionization selected ion flow tube mass spectrometry: Quantification and modelling of ion-molecule reactions.

The concentrations of aldehydes and volatile fatty acids have to be controlled because of their potential harmfulness in indoor air or relationship with the organoleptic properties of agri-food products. Although several specific analytical methods are currently used, the simultaneous analysis of these compounds in a complex matrix remains a challenge. The combination of positive and negative ionization selected ion flow tube mass spectrometry (SIFT-MS) allows the accurate, sensitive and high-frequency analysis of complex gas mixtures of these compounds. The ion-molecule reactions of negative precursor ions (OH- , O•- , O2 •- , NO2 - and NO3 - ) with five aldehydes and four carboxylic acids were investigated in order to provide product ions and rate constants for the quantification of these compounds by negative ion SIFT-MS. The results were compared with those obtained by conventional analysis methods and/or with already implemented SIFT-MS positive ionization methods. The modelling of hydroxide ion (OH- )/molecule reaction paths by ab-initio calculation allowed a better understanding of these gas-phase reactions. Deprotonation systematically occurs by reaction between negative ions and aldehydes or acids, leading to the formation of [M - H]- primary ions. Ab-initio calculations demonstrated the α-CH deprotonation of aldehydes and the acidic proton abstraction for fatty acids. For aldehydes, the presence of water in the flow tube leads to the formation of hydrated ions, [M - H]- .H2 O. With the NO2 - precursor ion, a second reaction channel results in ion-molecule association with the formation of M.NO2 - ions. Except for formaldehyde, all the studied compounds can be quantified by negative ion SIFT-MS with significant rate constants. In addition to positive ion SIFT-MS with H3 O+ , O2 + and NO+ precursor ions, negative ionization with O•- , O2 •- , OH- , NO2 - and NO3 - extends the range of analysis of aldehydes and carboxylic acids in air without a preparation or separation step. This methodology was illustrated by the simultaneous quantification in single-scan experiments of seven aldehydes and six carboxylic acids released by building materials.

Determination of kaurenoic acid in rat plasma using UPLC-MS/MS and its application to a pharmacokinetic study

Determination of kaurenoic acid in rat plasma using UPLC-MS/MS and its application to a pharmacokinetic study

D-region ion–neutral coupled chemistry (Sodankylä Ion Chemistry, SIC) within the Whole Atmosphere Community Climate Model (WACCM 4) – WACCM-SIC and WACCM-rSIC

Abstract. This study presents a new ion–neutral chemical model coupled into the Whole Atmosphere Community Climate Model (WACCM). The ionospheric D-region (altitudes ∼ 50–90 km) chemistry is based on the Sodankylä Ion Chemistry (SIC) model, a one-dimensional model containing 307 ion–neutral and ion recombination, 16 photodissociation and 7 photoionization reactions of neutral species, positive and negative ions, and electrons. The SIC mechanism was reduced using the simulation error minimization connectivity method (SEM-CM) to produce a reaction scheme of 181 ion–molecule reactions of 181 ion–molecule reactions of 27 positive and 18 negative ions. This scheme describes the concentration profiles at altitudes between 20 km and 120 km of a set of major neutral species (HNO3, O3, H2O2, NO, NO2, HO2, OH, N2O5) and ions (O2+, O4+, NO+, NO+(H2O), O2+(H2O), H+(H2O), H+(H2O)2, H+(H2O)3, H+(H2O)4, O3−, NO2−, O−, O2, OH−, O2−(H2O), O2−(H2O)2, O4−, CO3−, CO3−(H2O), CO4−, HCO3−, NO2−, NO3−, NO3−(H2O), NO3−(H2O)2, NO3−(HNO3), NO3−(HNO3)2, Cl−, ClO−), which agree with the full SIC mechanism within a 5 % tolerance. Four 3-D model simulations were then performed, using the impact of the January 2005 solar proton event (SPE) on D-region HOx and NOx chemistry as a test case of four different model versions: the standard WACCM (no negative ions and a very limited set of positive ions); WACCM-SIC (standard WACCM with the full SIC chemistry of positive and negative ions); WACCM-D (standard WACCM with a heuristic reduction of the SIC chemistry, recently used to examine HNO3 formation following an SPE); and WACCM-rSIC (standard WACCM with a reduction of SIC chemistry using the SEM-CM method). The standard WACCM misses the HNO3 enhancement during the SPE, while the full and reduced model versions predict significant NOx, HOx and HNO3 enhancements in the mesosphere during solar proton events. The SEM-CM reduction also identifies the important ion–molecule reactions that affect the partitioning of odd nitrogen (NOx), odd hydrogen (HOx) and O3 in the stratosphere and mesosphere.

Development of two step liquid-liquid extraction tandem UHPLC-MS/MS method for the simultaneous determination of Ginkgo flavonoids, terpene lactones and nimodipine in rat plasma: Application to the pharmacokinetic study of the combination of Ginkgo biloba dispersible tablets and Nimodipine tablets.

Development of two step liquid-liquid extraction tandem UHPLC-MS/MS method for the simultaneous determination of Ginkgo flavonoids, terpene lactones and nimodipine in rat plasma: Application to the pharmacokinetic study of the combination of Ginkgo biloba dispersible tablets and Nimodipine tablets.

A rapid and sensitive liquid chromatography-tandem mass spectrometry method for the quantitation of S-phenylmercapturic acid in human urine

A rapid, sensitive and robust method based on high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the quantitation of S-phenylmercapturic acid (S-PMA), a metabolite of benzene, in human urine. Urine samples to which S-phenylmercapturic acid-d2 (S-PMA-d2) had been added as an internal standard (I.S.) were subjected to liquid–liquid extraction (LLE) with ethyl acetate in an acidic environment. S-PMA and the I.S. were separated on a C18 column and detected in negative ion and multiple reaction monitoring mode within 1.8 min. The assay was fully validated and exhibited good linearity in the concentration range of 0.2–200 ng mL−1, with a lower limit of quantitation of 0.2 ng mL−1. The intra- and inter-day precisions were <8.1%, with a relative error <6.9%. The short run time coupled with the efficient one-step LLE sample preparation procedure makes the proposed method a promising strategy for the high-throughput and cost-effective analysis of urinary S-PMA levels, which is required to evaluate the health risk of exposure to benzene or cigarette smoking.

On the dynamics of chemical reactions of negative ions

This review discusses the dynamics of negative ion reactions with neutral molecules in the gas phase. Most anion–molecule reactions proceed via a qualitatively different interaction potential than cationic or neutral reactions. It has been and still is the goal of many experiments to understand these reaction dynamics and the different reaction mechanisms they lead to. We will show how rate coefficients and cross-sections for anion–molecule reactions are measured and interpreted to yield information on the underlying dynamics. We will also present more detailed approaches that study either the transient reaction complex or the energy- and angle-resolved scattering of negative ions with neutral molecules. With the help of these different techniques many aspects of anion–molecule reaction dynamics have been unravelled in the last few years. However, we are still far from a complete understanding of the complex molecular interplay that is at work during a negative ion reaction.

Reactions of Negative Ions with ClN3 at 300 K

The reactivity of ClN(3) with 17 negative ions has been investigated at 300 K. The electron affinity (EA) of ClN(3) was bracketed to be between that of NO(2) and N(3), giving EA(ClN(3)) = 2.48 +/- 0.20 eV, in agreement with an electronic structure calculation. Reaction rate constants and product ion branching ratios were measured. In nearly all cases the major product of the reaction was chloride ions. Charge transfer, N(3)(-) production, and O atom incorporation is also observed. DFT calculations of stable complexes and transition states are presented for two typical ions. Mechanistic details are discussed in terms of reaction coordinate diagrams.

Ion Chemistry of VX Surrogates and Ion Energetics Properties of VX: New Suggestions for VX Chemical Ionization Mass Spectrometry Detection

Room temperature rate constants and product ion branching ratios have been measured for the reactions of numerous positive and negative ions with VX chemical warfare agent surrogates representing the amine (triethylamine) and organophosphonate (diethyl methythiomethylphosphonate (DEMTMP)) portions of VX. The measurements have been supplemented by theoretical calculations of the proton affinity, fluoride affinity, and ionization potential of VX and the simulants. The results show that many proton transfer reactions are rapid and that the proton affinity of VX is near the top of the scale. Many proton transfer agents should detect VX selectively and sensitively in chemical ionization mass spectrometers. Charge transfer with NO(+) should also be sensitive and selective since the ionization potential of VX is small. The surrogate studies confirm these trends. Limits of detection for commercial and research grade CIMS instruments are estimated at 80 pptv and 5 ppqv, respectively.

Generation of negative ions in the gas phase from a 12CaO⋅7Al2O3 membrane-coated ceramic heater under atmospheric pressure

12 CaO ⋅ 7 Al 2 O 3 (C12A7) crystal is able to generate strong and high purity oxygen anion (O−) beam under reduced pressure. However, the emission of O− or related species under atmospheric pressure has not been evaluated. In this study, the characteristics of negative ion species emissions from the C12A7 membrane-coated ceramic heater under atmospheric pressure were investigated by quadrupole mass spectrometer. Negative ion species were confirmed to be emitted even under atmospheric pressure. It was supposed that the detected negative ion clusters, such as O−(H2O)n, O2−(H2O)n, and CO4−(H2O)n, were generated by the reaction of negative ions emitted from the heater with impurities in He gas.

Nonstandard Behavior of a Negative Ion Reaction at Very Low Temperatures

We have studied the negative ion reaction NH2-+H_{2}-->NH_{3}+H- in the temperature range from 300 to 8 K. We observe a strongly suppressed probability for proton transfer at room temperature. With decreasing temperature, this probability increases, in accordance with a longer lifetime of an intermediate anion-neutral complex. At low temperatures, a maximum in the reaction rate coefficient is observed that suggests the presence of a very small barrier at long range or a quantum mechanical resonance feature.

Reactions of small negative ions with O 2(a 1Δ g) and O 2(X 3Σ g−)

Reactions of small negative ions with O 2(a 1Δ g) and O 2(X 3Σ g−)

Quantification of puerarin in plasma by on-line solid-phase extraction column switching liquid chromatography–tandem mass spectrometry and its applications to a pharmacokinetic study

Quantification of puerarin in plasma by on-line solid-phase extraction column switching liquid chromatography–tandem mass spectrometry and its applications to a pharmacokinetic study

Inelastic electron scattering and energy-selective negative ion reactions in molecular films on silicon surfaces

Inelastic electron scattering and energy-selective negative ion reactions in molecular films on silicon surfaces

Dissociative electron attachment to gas phase glycine: Exploring the decomposition pathways by mass separation of isobaric fragment anions

Dissociative electron attachment to gas phase glycine generates a number of fragment ions, among them ions observed at the mass numbers 15, 16 and 26 amu. From stoichiometry they can be assigned to the chemically rather different species NH(-)/CH(3)(-)(15 amu), O(-)/NH(2)(-)(16 amu) and CN(-)/C(2)H(2)(-)(26 amu). Here we use a high resolution double focusing two sector mass spectrometer to separate these isobaric ions. It is thereby possible to unravel the decomposition reactions of the different transient negative ions formed upon resonant electron attachment to neutral glycine in the energy range 0-15 eV. We find that within the isobaric ion pairs, the individual components generally arise from resonances located at substantial different energies. The corresponding unimolecular decompositions involve complex reaction sequences including multiple bond cleavages and substantial rearrangement in the precursor ion. To support the interpretation and assignments we also use (13)C labelling of glycine at the carboxylic group.