A New Method for Measuring the Diffusion Coefficient in a Gas Phase

Rouholahnejad, Fereshteh; Tabrizchi, Mahmoud

doi:10.1021/jp061492q

Cited by 4 publications

(2 citation statements)

References 20 publications

(27 reference statements)

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“…Hence present algorithms will also be useful to calculate the diffusion coefficients of gas-phase species (ions or neutrals). Comparison of those values with measured diffusion properties − may provide structural information 51,52 that, for neutrals, is not obtainable by IMS.…”

Section: Discussionmentioning

confidence: 99%

Optimization of Algorithms for Ion Mobility Calculations

et al. 2007

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Ion mobility spectrometry (IMS) is increasingly employed to probe the structures of gas-phase ions, particularly those of proteins and other biological macromolecules. This process involves comparing measured mobilities to those computed for potential geometries, which requires evaluation of orientationally averaged cross sections using some approximate treatment of ion-buffer gas collisions. Two common models are the projection approximation (PA) and exact hard-spheres scattering (EHSS) that represent ions as collections of hard spheres. Though calculations for large ions and/or conformer ensembles take significant time, no algorithmic optimization had been explored. Previous EHSS programs were dominated by ion rotation operations that allow orientational averaging. We have developed two new algorithms for PA and EHSS calculations: one simplifies those operations and greatly reduces their number, and the other disposes of them altogether by propagating trajectories from a random origin. The new algorithms were tested for a representative set of seven ion geometries including diverse sizes and shapes. While the best choice depends on the geometry in a nonobvious way, the difference between the two codes is generally modest. Both are much more efficient than the existing software, for example faster than the widely used Mobcal (implementing EHSS) approximately 10-30-fold.

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Section: Discussionmentioning

confidence: 99%

Optimization of Algorithms for Ion Mobility Calculations

et al. 2007

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“…Such methods tend to be tedious, expensive, and time-consuming. This motivates the search for alternatives, which are often indirect methods that infer the diffusivity from the measurements of more easily accessible properties affected by mass transfer, such as pressure, interface velocity, volume of the diffusing solute, NMR spin echos, and others. − For instance, by tracking the motion of the interface, the diffusion coefficient of carbon dioxide in crude oil can be obtained . Measurement of pressure at constant volume was used to characterize gas diffusivity into bitumen .…”

Section: Introductionmentioning

confidence: 99%

Diffusivity Measurements of Solutes Impacting Interfacial Tension

Chernyshev

Skliar

2015

Ind. Eng. Chem. Res.

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We propose a method for measuring gas and liquid diffusivities of surface active solutes based on the measurements of dynamic interfacial tension. The selection of the experimental system needed to achieve accurate diffusivity estimation and, particularly, the selection of the complementary fluid to create the interface sensitive to the solute concentration are emphasized. The method is applicable to solutes beyond traditional liquid-phase surfactants and is demonstrated by estimating diffusivities of several vapors in air. Though the method allows for surface active compounds that traverse the interface, the procedure for estimating diffusion coefficients is particularly simple in cases when the solute is insoluble in the complementary fluid and when its flux across the interface is small. It was shown that by adding surfactants to the complementary fluid, it may be possible to reduce the flux of the solute across the interface by increasing the resistance to cross-interfacial transport and to identify diffusivities with higher accuracy based on simple data analysis. The improved accuracy is also achieved when the diffusivity is identified based on models that, when appropriate, account for the absorption of the solute into the complementary fluid. The developed method is simple, rapid, suitable for many applications, and often can be implemented using only basic laboratory equipment. We discuss its advantages, limitations, and provide user guidelines for its implementation.

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