A Study of Ion—molecule Reactions in the Xe+ + Acetone System by Flow Technique Mass Spectrometry

2002 ◽  
Vol 8 (2) ◽  
pp. 147-156 ◽  
Author(s):  
P.S. Vinogradov ◽  
A.S. Misharin
Keyword(s):  
Mass Spectrometry ◽  
Rate Constants ◽  
Flow Reactor ◽  
Ionic Composition ◽  
Kinetic Scheme ◽  
Effective Rate ◽  
Fourth Generation ◽  
Buffer Gas ◽  
Acetone Concentration ◽  
Subsequent Transformation

Flow reactor technique mass spectrometry was used to study the reaction of Xe+ ions with acetone and the subsequent transformation of the product ions at a buffer gas (He) pressure of 1.1 Torr. A kinetic scheme describing the evolution of the ionic composition of the most abundant ionic constituents (up to the fourth generation) has been determined. The values of rate constants and branching ratios of the key reactions involved in the scheme have been evaluated from experimental kinetic dependences. The main channel of the Xe+ + acetone reaction (which occurs practically at each collision) is the production of the CH3CO+ fragment as the exothermicity of the charge transfer is higher than the dissociation threshold of the ground state acetone cation. The formation of a 2.5% fraction of the molecular ion via a parallel channel indicates that the production of an electronically-excited, long-lived state of the acetone cation takes place. The competition of association and particle-rearrangement processes in the reactions of the CH3CO+ ion and its CH3CO+(CH3)2CO cluster with acetone was also studied. It was found that channels in which a rearrangement of particles takes place (the production of protonated acetone for CH3CO+ and the protonated acetone dimer for CH3CO+(CH3)2CO) are slower than the association process at 1.1 Torr. Total effective rate constants (involving all the channels) for these ions are approximately several 10−10 cm3 s−1 units and the rate constant for the cluster ion is about 40% smaller. The production of slowly reacting C3H6O+ ions with an increase of acetone concentration was observed. Their structure may be ascribed to the enolic acetone cation (CH2COHCH3+). The only pathway for the loss of the ion in an exoergic reaction with acetone is the association process. The product of the process, i.e. the non-protonated ionic dimer of acetone, was also observed in the mass spectra.

scholarly journals FREE RADICALS BY MASS SPECTROMETRY: XXXIV. A FLOW REACTOR FOR MEASUREMENT OF FAST THERMAL REACTIONS

1966 ◽  
Vol 44 (18) ◽  
pp. 2205-2210 ◽  
Author(s):  
I. P. Fisher ◽  
J. B. Homer ◽  
B. Roberts ◽  
F. P. Lossing
Keyword(s):  
Mass Spectrometry ◽  
Thermal Decomposition ◽  
Free Radicals ◽  
Rate Constants ◽  
Flow Reactor ◽  
Residence Times ◽  
Thermal Reactions ◽  
New Type ◽  
Good Agreement ◽  
Gas Pressures

A new type of flow reactor for use with a mass spectrometer has been constructed, in which many of the disadvantages of flow systems for rate measurements have been overcome. Rate constants for unimolecular decompositions can be measured in the range 50 – 5 000 s−1, with helium carrier gas pressures of 10–50 mm and residence times of 10−3 to 10−1 s. Measurements of the rate of thermal decomposition of trioxane are in good agreement with the rates predicted from literature data obtained at much lower temperatures.

PLATELET AGGREGATION DOES NOT CONFORM TO SIMPLE PARTICLE COLLISION THEORY

1987 ◽  
Author(s):  
Moideen P Jamaluddin
Keyword(s):  
Platelet Aggregation ◽  
Rate Equation ◽  
Rate Constants ◽  
Kinetic Scheme ◽  
Order Type ◽  
Second Order ◽  
Particle Collision ◽  
Collision Theory ◽  
Rate Law ◽  
First Order

Platelet aggregation kinetics, according to the particle collision theory, generally assumed to apply, ought to conform to a second order type of rate law. But published data on the time-course of ADP-induced single platelet recruitment into aggregates were found not to do so and to lead to abnormal second order rate constants much larger than even their theoretical upper bounds. The data were, instead, found to fit a first order type of rate law rather well with rate constants in the range of 0.04 - 0.27 s-1. These results were confirmed in our laboratory employing gelfiltered calf platelets. Thus a mechanism much more complex than hithertofore recognized, is operative. The following kinetic scheme was formulated on the basis of information gleaned from the literature.where P is the nonaggregable, discoid platelet, A the agonist, P* an aggregable platelet form with membranous protrusions, and P** another aggregable platelet form with pseudopods. Taking into account the relative magnitudes of the k*s and assuming aggregation to be driven by hydrophobic interaction between complementary surfaces of P* and P** species, a rate equation was derived for aggregation. The kinetic scheme and the rate equation could account for the apparent first order rate law and other empirical observations in the literature.

An ICR mass spectrometry study of ion/molecule reactions between ethyl chloride and alkylamines

1991 ◽  
Vol 69 (2) ◽  
pp. 363-367
Author(s):  
Guoying Xu ◽  
Jan A. Herman
Keyword(s):  
Mass Spectrometry ◽  
Key Words ◽  
Rate Constant ◽  
Rate Constants ◽  
Ethyl Chloride ◽  
Ion Molecule Reactions ◽  
Mass Spectrometry Study ◽  
Ethyl Cation

Ion/molecule reactions in mixtures of ethyl chloride with C1–C4 alkylamines were studied by ICR mass spectrometry. Ethyl cation transfer to C1–C4 alkylamines proceeds mainly through diethylchloronium ions with rate constants ~3 × 10−10cm3 s−1. In the case of s-butylamine the corresponding rate constant is 0.5 × 10−10 cm3 s−1. Key words: ICR mass spectrometry, ion/molecule reactions, ethylchloride, methylamine, ethylamine, propylamines, butylamines

scholarly journals Accurate modelling of small-scale linear ion trap operating mode using He buffer gas to improve sensitivity and resolution for in-the-field mass spectrometry

2019 ◽  
Vol 34 (8) ◽  
pp. 1672-1682 ◽  
Author(s):  
Aurika Janulyte ◽  
Yves Zerega ◽  
Boris Brkić ◽  
Stephen Taylor ◽  
Jacques Andre
Keyword(s):  
Mass Spectrometry ◽  
Ion Trap ◽  
Operating Mode ◽  
Small Scale ◽  
Buffer Gas ◽  
Linear Ion Trap ◽  
Field Mass

Improved sensitivity and resolution of a small-scale linear ion trap is observed using He buffer.

scholarly journals A new aerosol flow reactor to study secondary organic aerosol

2019 ◽  
Vol 12 (8) ◽  
pp. 4519-4541 ◽  
Author(s):  
Kelly L. Pereira ◽  
Grazia Rovelli ◽  
Young C. Song ◽  
Alfred W. Mayhew ◽  
Jonathan P. Reid ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Liquid Chromatography ◽  
Chemical Composition ◽  
Relative Humidity ◽  
Single Particle ◽  
Physical State ◽  
Flow Reactor ◽  
Organic Aerosol ◽  
Physiochemical Properties ◽  
Formation Conditions

Abstract. Gas-particle equilibrium partitioning is a fundamental concept used to describe the growth and loss of secondary organic aerosol (SOA). However, recent literature has suggested that gas-particle partitioning may be kinetically limited, preventing volatilization from the aerosol phase as a result of the physical state of the aerosol (e.g. glassy, viscous). Experimental measurements of diffusion constants within viscous aerosol are limited and do not represent the complex chemical composition observed in SOA (i.e. multicomponent mixtures). Motivated by the need to address fundamental questions regarding the effect of the physical state and chemical composition of a particle on gas-particle partitioning, we present the design and operation of a newly built 0.3 m3 continuous-flow reactor (CFR), which can be used as a tool to gain considerable insights into the composition and physical state of SOA. The CFR was used to generate SOA from the photo-oxidation of α-pinene, limonene, β-caryophyllene and toluene under different experimental conditions (i.e. relative humidity, VOC and VOC∕NOx ratios). Up to 102 mg of SOA mass was collected per experiment, allowing the use of highly accurate compositional- and single-particle analysis techniques, which are not usually accessible due to the large quantity of organic aerosol mass required for analysis. A suite of offline analytical techniques was used to determine the chemical composition and physical state of the generated SOA, including attenuated total reflectance infrared spectroscopy; carbon, hydrogen, nitrogen, and sulfur (CHNS) elemental analysis; 1H and 1H-13C nuclear magnetic resonance spectroscopy (NMR); ultra-performance liquid chromatography ultra-high-resolution mass spectrometry (UHRMS); high-performance liquid chromatography ion-trap mass spectrometry (HPLC-ITMS); and an electrodynamic balance (EDB). The oxygen-to-carbon (O∕C) and hydrogen-to-carbon (H∕C) ratios of generated SOA samples (determined using a CHNS elemental analyser) displayed good agreement with literature values and were consistent with the characteristic Van Krevelen diagram trajectory, with an observed slope of −0.41. The elemental composition of two SOA samples formed in separate replicate experiments displayed excellent reproducibility, with the O∕C and H∕C ratios of the SOA samples observed to be within error of the analytical instrumentation (instrument accuracy ±0.15 % to a reference standard). The ability to use a highly accurate CHNS elemental analyser to determine the elemental composition of the SOA samples allowed us to evaluate the accuracy of reported SOA elemental compositions using UHRMS (a commonly used technique). In all of the experiments investigated, the SOA O∕C ratios obtained for each SOA sample using UHRMS were lower than the O∕C ratios obtained from the CHNS analyser (the more accurate and non-selective technique). The average difference in the ΔO∕C ratios ranged from 19 % to 45 % depending on the SOA precursor and formation conditions. α-pinene SOA standards were generated from the collected SOA mass using semi-preparative HPLC-ITMS coupled to an automated fraction collector, followed by 1H NMR spectroscopy. Up to 35.8±1.6 % (propagated error of the uncertainty in the slope of the calibrations graphs) of α-pinene SOA was quantified using this method; a considerable improvement from most previous studies. Single aerosol droplets were generated from the collected SOA samples and trapped within an EDB at different temperatures and relative humidities to investigate the dynamic changes in their physiochemical properties. The volatilization of organic components from toluene and β-caryophyllene SOA particles at 0 % relative humidity was found to be kinetically limited, owing to particle viscosity. The unconventional use of a newly built CFR, combined with comprehensive offline chemical characterization and single-particle measurements, offers a unique approach to further our understanding of the relationship between SOA formation conditions, chemical composition and physiochemical properties.

scholarly journals Improved resolution of single channel dwell times reveals mechanisms of binding, priming, and gating in muscle AChR

2016 ◽  
Vol 148 (1) ◽  
pp. 43-63 ◽  
Author(s):  
Nuriya Mukhtasimova ◽  
Corrie J.B. daCosta ◽  
Steven M. Sine
Keyword(s):  
Rate Constants ◽  
Single Channel ◽  
Partial Agonist ◽  
Equilibrium Constants ◽  
Channel Gating ◽  
Kinetic Scheme ◽  
Step Response ◽  
Forward Rate ◽  
Gain Of Function ◽  
Single Channel Currents

The acetylcholine receptor (AChR) from vertebrate skeletal muscle initiates voluntary movement, and its kinetics of activation are crucial for maintaining the safety margin for neuromuscular transmission. Furthermore, the kinetic mechanism of the muscle AChR serves as an archetype for understanding activation mechanisms of related receptors from the Cys-loop superfamily. Here we record currents through single muscle AChR channels with improved temporal resolution approaching half an order of magnitude over our previous best. A range of concentrations of full and partial agonists are used to elicit currents from human wild-type and gain-of-function mutant AChRs. For each agonist–receptor combination, rate constants are estimated from maximum likelihood analysis using a kinetic scheme comprised of agonist binding, priming, and channel gating steps. The kinetic scheme and rate constants are tested by stochastic simulation, followed by incorporation of the experimental step response, sampling rate, background noise, and filter bandwidth. Analyses of the simulated data confirm all rate constants except those for channel gating, which are overestimated because of the established effect of noise on the briefest dwell times. Estimates of the gating rate constants were obtained through iterative simulation followed by kinetic fitting. The results reveal that the agonist association rate constants are independent of agonist occupancy but depend on receptor state, whereas those for agonist dissociation depend on occupancy but not on state. The priming rate and equilibrium constants increase with successive agonist occupancy, and for a full agonist, the forward rate constant increases more than the equilibrium constant; for a partial agonist, the forward rate and equilibrium constants increase equally. The gating rate and equilibrium constants also increase with successive agonist occupancy, but unlike priming, the equilibrium constants increase more than the forward rate constants. As observed for a full and a partial agonist, the gain-of-function mutation affects the relationship between rate and equilibrium constants for priming but not for channel gating. Thus, resolving brief single channel currents distinguishes priming from gating steps and reveals how the corresponding rate and equilibrium constants depend on agonist occupancy.

Kinetic Studies of Hydrodeoxygenation of Ethyl Ester of Decane Acid over a Ni-Cu-Mo/Al2O3 Catalyst

2019 ◽  
Vol 19 (1) ◽  
pp. 33-39
Author(s):  
R. G. Kukushkin ◽  
S. I. Reshetnikov ◽  
S. G. Zavarukhin ◽  
P. M. Eletskiy ◽  
V. A. Yakovlev
Keyword(s):  
Contact Time ◽  
Noble Metals ◽  
Flow Reactor ◽  
Experimental Studies ◽  
Kinetic Studies ◽  
Nickel Catalysts ◽  
Effective Rate ◽  
Main Reaction ◽  
Reaction Products ◽  
Fixed Catalyst

Nickel-based catalysts for hydrodeoxygenation of vegetable oils are an alternative to the systems based on noble metals and sulfide catalysts for hydrotreatment. Modification of the nickel catalysts with molybdenum and copper allows the yield of target products to be increased and the corrosion resistance of the catalytic system to be improved. The studies were aimed at establishing relationships between temperature, contact time and activity of the modified nickel-containing catalyst to hydroxygenation of esters of fatty carboxylic acids, as well as at determining effective kinetic parameters of the reactant consumption. A flow reactor with the fixed catalyst bed was used for experimental studies at РН2 = 0.25 MPa, temperatures 270, 285, 300 and 315 °C, contact time varied from 600 to 1800 s. It was shown that the selectivity to the main reaction products – nonane and decane – did not change upon varying the reaction temperature and contact time. The experimental data were used for determining the effective rate constants and activation energy of the reaction.

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