Robust and high‐resolution simulations of nonlinear electrokinetic processes in variable cross‐section channels

Bahga, Supreet Singh; Bercovici, Moran; Santiago, Juan G.

doi:10.1002/elps.201200264

Cited by 27 publications

(50 citation statements)

References 37 publications

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“…The LE is composed of 100 mM sodium hydroxide and 200 mM Hepes. Based on one-dimensional numerical simulations using the Stanford public release electrophoretic separation solver (SPRESSO) [23,24] along with ionic strength corrections [25], the TE zone behind the shock wave is composed of 72.48 mM Bistris and 172.5 mM Hepes. For this ITP system, numerical simulations predict that μ L = 42.6 × 10 −9 m 2 V −1 s −1 , μ T = 7.77 × 10 −9 m 2 V −1 s −1 , σ L = 0.5617 S m −1 , and σ T = 0.1024 S m −1 .…”

Section: Resultsmentioning

confidence: 99%

Electrohydrodynamic instability of ion-concentration shock wave in electrophoresis

Gaur

Bahga

2017

Phys. Rev. E

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Capillary electrophoresis techniques often involve ion-concentration shock waves in an electrolyte solution, propagating under the effect of an external electric field. These shock waves are characterized by self-sharpening gradients in ion concentrations and electrical conductivity that are collinear with the electric field. The coupling of electric field and fluid motion at the shock interface sometimes leads to an undesirable electrohydrodynamic (EHD) instability. Using linear stability analysis, we describe the motion of small-amplitude disturbances of an electrophoretic shock wave. Our analysis shows that the EHD instability results due to the competition between destabilizing electroviscous flow and stabilizing electromigration of the shock wave. The ratio of timescales corresponding to electroviscous flow and electromigration yields a threshold criterion for the onset of instability. We present a validation of this threshold criterion with published experimental data and also describe the physical mechanism underlying the EHD instability of the electrophoretic shock wave.

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Section: Resultsmentioning

confidence: 99%

Electrohydrodynamic instability of ion-concentration shock wave in electrophoresis

Gaur

Bahga

2017

Phys. Rev. E

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“…This suggests that for Pe = 10, both diffusive and convective effects are relevant and hence it marks the transition between diffusion‐ and convection‐dominated regimes. Besides these 2D simulations, in the Supporting Information, we also provide 1D simulations of FASS using SPRESSO (Stanford Public Release Electophoretic Separation Solver) simulation tool for the case when EOF is absent. These 1D simulations also confirm the scaling behavior predicted by Eq.…”

Section: Theorymentioning

confidence: 99%

Scaling behavior in on‐chip field‐amplified sample stacking

2019

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Field amplified sample stacking (FASS) uses differential electrophoretic velocity of analyte ions in the high‐conductivity background electrolyte zone and low conductivity sample zone for increasing the analyte concentration. The stacking rate of analyte ions in FASS is limited by molecular diffusion and convective dispersion due to nonuniform electroosmotic flow (EOF). We present a theoretical scaling analysis of stacking dynamics in FASS and its validation with a large set of on‐chip sample stacking experiments and numerical simulations. Through scaling analysis, we have identified two stacking regimes that are relevant for on‐chip FASS, depending upon whether the broadening of the stacked peak is dominated by axial diffusion or convective dispersion. We show that these two regimes are characterized by distinct length and time scales, based on which we obtain simplified nondimensional relations for the temporal growth of peak concentration and width in FASS. We first verify the theoretical scaling behavior in diffusion‐ and convection‐dominated regimes using numerical simulations. Thereafter, we show that the experimental data of temporal growth of peak concentration and width at varying electric fields, conductivity gradients, and EOF exhibit the theoretically predicted scaling behavior. The scaling behavior described in this work provides insights into the effect of varying experimental parameters, such as electric field, conductivity gradient, electroosmotic mobility, and electrophoretic mobility of the analyte on the dynamics of on‐chip FASS.

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“…(39), respectively, against numerical solution obtained from SPRESSO 35 using the SLIP mode scheme. 36 We use a common ITP buffer chemistry, with HCl as the leading ion, Hepes as the trailing ion, and Tris as the common counter ion. Using the same background chemistry, we compare the analyte distribution obtained for three analyte mobilities of 24, 45, and 33 (in units 10 −9 [m 2 V −1 sec −1 ]).…”

Section: Exact and Approximate Solutions For Analyte Concentratiomentioning

confidence: 99%

Sample distribution in peak mode isotachophoresis

2014

Self Cite

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We present an analytical study of peak mode isotachophoresis (ITP), and provide closed form solutions for sample distribution and electric field, as well as for leading-, trailing-, and counter-ion concentration profiles. Importantly, the solution we present is valid not only for the case of fully ionized species, but also for systems of weak electrolytes which better represent real buffer systems and for multivalent analytes such as proteins and DNA. The model reveals two major scales which govern the electric field and buffer distributions, and an additional length scale governing analyte distribution. Using well-controlled experiments, and numerical simulations, we verify and validate the model and highlight its key merits as well as its limitations. We demonstrate the use of the model for determining the peak concentration of focused sample based on known buffer and analyte properties, and show it differs significantly from commonly used approximations based on the interface width alone. We further apply our model for studying reactions between multiple species having different effective mobilities yet co-focused at a single ITP interface. We find a closed form expression for an effective-on rate which depends on reactants distributions, and derive the conditions for optimizing such reactions. Interestingly, the model reveals that maximum reaction rate is not necessarily obtained when the concentration profiles of the reacting species perfectly overlap. In addition to the exact solutions, we derive throughout several closed form engineering approximations which are based on elementary functions and are simple to implement, yet maintain the interplay between the important scales. Both the exact and approximate solutions provide insight into sample focusing and can be used to design and optimize ITP-based assays.

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Robust and high‐resolution simulations of nonlinear electrokinetic processes in variable cross‐section channels

Cited by 27 publications

References 37 publications

Electrohydrodynamic instability of ion-concentration shock wave in electrophoresis

Electrohydrodynamic instability of ion-concentration shock wave in electrophoresis

Scaling behavior in on‐chip field‐amplified sample stacking

Sample distribution in peak mode isotachophoresis

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