A method to determine quasi‐steady state in constant voltage mode isotachophoresis

Abstract

Identification of the steady state is very challenging in isotachophoresis (ITP); especially in complex microgeometries, such as dog-leg channels or cross-channel junctions. In this work, an elastic matching method is applied to determine the quasi-steady state in microscale ITP. In the elastic matching method, the similarity between two profiles is calculated by comparing intensity distribution of two images or profiles. To demonstrate this similarity-based analysis technique for ITP, a constant voltage mode ITP model is developed and applied to a five-component ITP system. Hydrochloric acid and caproic acid are used as the leader and terminator, respectively, while histidine is used as the counter-ion. Two sample components, acetic acid and benzoic acid, are separated under the action of an applied electric field in both straight and dog-leg microchannels. This analysis shows that conductivity profiles provide a better measure to determine the quasi-steady state in an ITP process. For a straight microchannel, the quasi-steady state is achieved in less than a minute with a total potential drop of 100 V in a 2 cm long channel. In a straight channel, a true steady state can be achieved for ITP with appropriate countercurrent flow where stationary zones are formed, but the time it takes to reach the steady state is much longer than the without counter flow case. The numerical results indicate that a steady state cannot be reached in a dog-leg microchannel because of sample dispersion and refocusing at and near the intersections and at the branch channels. However, the elastic matching method can be used to determine the quasi-steady state in a dog-leg microchannel.

Dynamic computer simulations of electrophoresis: 2010–2020

“…Electrophoretic mobilization toward the cathode was induced by replacing the cathodic electrode solution with the anolyte followed by a continuation of power application at 600 V for 700 s. The detector plot for the 14 analytes and a detector placed at 57.6 mm is presented as insert in panel D. The cathode is to the right. Key: 1, serotonin (pI 10.58); 2, tyramine (10.17 • Parallel implementation with multiple CPUs for IEF simulations [85] and parallel scheme efficient algorithm for 2D IEF [86] • Effect of Joule heating on IEF [88] • 2D model for free flow IEF [89] • 2D model of ITP in channels of changing cross-sectional area [91]; quasi-steady state of ITP in complex microgeometries [92] and effect of Joule heating in ITP [93] CFD-ACE+ with user models Finite-element • Effects of electrode configuration and setting on electrokinetic analyte injection in CZE [94,95] • Analyte behavior in a curved channel [96] • Electrokinetic supercharging [97], behavior of DNA in CGE after electrokinetic injection [98], conditions at the capillary tip during field-amplified sample injection [99] • pH gradient formation and cathodic drift in microchip [100]…”

“…With a proper change of the boundary conditions at the column ends, the same approach could be employed for studying the ITP process in straight channels [ 90 ] and in those featuring changes of the cross‐sectional area [ 91 ]. Furthermore, the 2D model was applied to determine a quasi‐steady state in complex microgeometries operated under constant voltage [ 92 ] and was extended to include temperature effects in the constant voltage mode of ITP in a microchannel [ 93 ].…”

“…2D model of ITP in channels of changing cross‐sectional area [ 91 ]; quasi‐steady state of ITP in complex microgeometries [ 92 ] and effect of Joule heating in ITP [ 93 ]…”

Recent progress in analytical capillary isotachophoresis

“…Results for a contraction and expansion channel and comparison with a regular channel were presented only in form of 1D profiles along the separation direction and show thus expectable results. The simulation method was further used to investigate the possibilities to reach ITP steady state in complex microgeometries. The results comparing a straight channel with or without counterflow and a dog‐leg channel show that in the latter channel type a steady state cannot be reached because of sample dispersion and refocusing at and near the intersections and at the branch channels.…”