Electrokinetic Migration Research Articles

Self-powered Pb(II) removal driven by Zn-air batteries using N, P-doped active straw carbon as cathode

Electrochemical systems have been widely applied in heavy-metal ions (HMIs) pollution control, while their applications are greatly restricted by excessive energy consumption. Self-powered environmental remediation systems (SERSs) can shed the energy reliance to achieve HMIs decontamination and simultaneous electricity output through electrokinetic migration. In this work, SERSs based on Zn-air batteries (ZABs) were achieved to remove bivalent lead (Pb(II)) by circulating effluent as electrolyte. Straw biomass derived N, P functional active nanocarbon (NP-ASC) with hierarchical porosity and electron modulation effect was designed for achieving high oxygen reduction reaction (ORR) activity and efficient Pb(II) uptake. SERSs with electrode active area of 1 cm2 realize outstanding Pb(II) removal efficiency (98.1 %) and electricity generation (67.5 mWh∙cm−2) in simulated sewage. ZABs assembled with NP-ASC delivered specific capacity of 795 mAh∙g−1 and cycling stability for 340 h. This study provides a guide for designing a novel SERS using functionalized biomass nanocarbon.

Recent elaborations in electromembrane microextraction technique for preconcentration of chromium species: A mini-review

In recent years, electromembrane microextraction techniques have been used widely for the analysis of chromium species (trivalent and hexavalent chromium) in different environmental matrices. It is based on the electrokinetic migration across a membrane under the effect of an external electrical field between two aqueous phases. Trace analysis in complex matrices usually requires an effective sample preparation step to isolate, extract, and enrich the target analytes. Due to its distinctive qualities, including a high degree of enrichment factors, clean-up, and conformity with green chemistry principles, electromembrane microextraction techniques are among the methods for extracting chromium that have gained much attention in recent years. These techniques could be classified into two groups; electromembrane extraction (EME) which is based on using hydrophobic compounds (e.g., a few microliters of organic solvents) to separate the two aqueous solutions (donor and acceptor solutions), and gel electromembrane microextraction (G-EME) which is based on using a membrane made of biopolymers. In this review, the most recent advancements in EME and G-EME technologies for the extraction of chromium species in environmental samples in the last five years were summarized. Furthermore, the performance of the systems is evaluated in terms of their precision and accuracy, detection limits, and merits and drawbacks. Finally, future perspectives on these techniques were discussed.

Environmental Applications of Electromembrane Extraction: A Review.

Electromembrane extraction (EME) is a miniaturized extraction technique that has been widely used in recent years for the analysis and removal of pollutants in the environment. It is based on electrokinetic migration across a supported liquid membrane (SLM) under the influence of an external electrical field between two aqueous compartments. Based on the features of the SLM and the electrical field, EME offers quick extraction, effective sample clean-up, and good selectivity, and limits the amount of organic solvent used per sample to a few microliters. In this paper, the basic devices (membrane materials and types of organic solvents) and influencing factors of EME are first introduced, and the applications of EME in the analysis and removal of environmental inorganic ions and organic pollutants are systematically reviewed. An outlook on the future development of EME for environmental applications is also given.

Electromembrane Extraction of Naphthenic Acids in Produced Water Followed by Ultra-High-Resolution Mass Spectrometry Analysis.

Naphthenic acids comprise one of the most toxic compounds of the produced water released from offshore oil platforms. Therefore, developing and applying faster, simpler, and more efficient analytical methods for analyzing naphthenic acids are urgently needed. Electromembrane extraction (EME) uses the electrokinetic migration of target ions through a porous membrane. Herein, the EME method was applied to extract naphthenic acids from produced water. The EME method was optimized, and the optimal conditions encompassed decanol as the organic solvent, the sample with pH 10.0, 5 min of extraction at 200 V, and the ratio 4:1 (borate buffer/matrix, v/v). Electrochemical impedance spectroscopy confirmed charged species' migration from produced water through the EME. Subsequently, all extracts were analyzed by ultra-high-resolution mass spectrometry. The EME efficiency was assessed by comparing the extraction results to the liquid-liquid extraction (LLE) method results. Analytical results showed good linearity for both solvent and matrix curves (R2 > 0.98). Low detection limits ranged from 0.10 to 0.13 μg mL-1 and quantification limits from 0.36 to 0.45 μg mL-1. Precision and accuracy values ranged from -13.3% to 16.5%. These values fit the proposed method, demonstrating that the EME was more efficient than LLE in naphthenic acid extraction. The EME method preferably extracted aromatic compounds with double-bond equivalence from 6 to 8. The EME coupled with ultra-high-resolution mass spectrometry was demonstrated as a promising analytical approach to naphthenic acid extraction as an efficient and more environmentally friendly alternative to conventional extraction methods.

Numerical study of dielectrophoresis-modified inertial migration for overlapping sized cell separation.

Circulating tumor cells (CTCs) have been proven to have significant prognostic, diagnostic, and clinical values in early-stage cancer detection and treatment. The efficient separation of CTCs from peripheral blood can ensure intact and viable CTCs and can, thus, give proper genetic characterization and drug innovation. In this study, continuous and high-throughput separation of MDA-231 CTCs from overlapping sized white blood cells (WBCs) is achieved by modifying inertial cell focusing with dielectrophoresis (DEP) in a single-stage microfluidic platform by numeric simulation. The DEP is enabled by embedding interdigitated electrodes with alternating field control on a serpentine microchannel to avoid creating two-stage separation. Rather than using the electrokinetic migration of cells which slows down the throughput, the system leverages the inertial microfluidic flow to achieve high-speed continuous separation. The cell migration and cell positioning characteristics are quantified through coupled physics analyses to evaluate the effects of the applied voltages and Reynolds numbers (Re) on the separation performance. The results indicate that the introduction of DEP successfully migrates WBCs away from CTCs and that separation of MDA-231 CTCs from similar sized WBCs at a high Re of 100 can be achieved with a low voltage of magnitude 4 ×106 V/m. Additionally, the viability of MDA-231 CTCs is expected to be sustained after separation due to the short-term DEP exposure. The developed technique could be exploited to design active microchips for high-throughput separation of mixed cell beads despite their significant size overlap, using DEP-modified inertial focusing controlled simply by adjusting the applied external field.

Application of sulfide-modified nanoscale zerovalent iron electrodes for electrokinetic remediation of chromium-contaminated soil in a three-dimensional electrode system

A modified electrokinetic remediation (EKR) system was designed to remediate Cr-contaminated soil using sulfidated nano-scale zerovalent iron (S-nZVI) as the third electrode. This study systematically compared the technological parameters and remediation efficiencies of three-dimensional (3D) electrokinetic systems using different materials as the third electrodes. The comparative experiment showed that the 3D EKR could effectively increase current efficiency, balance voltage distribution, alleviate excessive acidification or alkalization of soils and effectively improve the removal efficiency of Cr. Compared with other 3D electrodes, the S-nZVI electrode led to the higher currents and the more uniform voltage distribution; additionally, the leaching toxicities were reduced by 50.0–66.7%, and the removal efficiencies of total Cr (Cr(tot)) and hexavalent Cr (Cr(VI)) were increased by at least 15.4% and 22.6%, respectively. Cr(VI) was removed mainly resulting from the electrokinetic migration. Meanwhile, a small amount of Cr(Ⅵ) was converted to FeCr2O4 and Cr3+OOH after reacting with S-nZVI in the middle region of the 3D EKR system. Due to the active layer of iron sulfides, S-nZVI was more stable and its electrokinetic efficiency was higher than other 3D electrodes, resulting in higher overall removal efficiencies. 3D EKR with S-nZVI can effectively decrease the toxicological effect of Cr contaminated soil at an experimental scale. The experimental findings from this study may provide a reference for guiding the development of more efficient methods for Cr-contaminated soil treatment.

Electromembrane extraction of polar substances – Status and perspectives

In this article, the scientific literature on electromembrane extraction (EME) of polar substances (log P < 2) is reviewed. EME is an extraction technique based on electrokinetic migration of analyte ions from an aqueous sample, across an organic supported liquid membrane (SLM), and into an aqueous acceptor solution. Because extraction is based on voltage-assisted partitioning, EME is fundamentally suitable for extraction of polar and ionizable substances that are challenging in many other extraction techniques. The article provides an exhaustive overview of papers on EME of polar substances. From this, different strategies to improve the mass transfer of polar substances are reviewed and critically discussed. These strategies include different SLM chemistries, modification of supporting membranes, sorbent additives, aqueous solution chemistry, and voltage/current related strategies. Finally, the future applicability of EME for polar substances is discussed. We expect EME in the coming years to be developed towards both very selective targeted analysis, as well as untargeted analysis of polar substances in biomedical applications such as metabolomics and peptidomics.

Enrichment of psychotropic drugs using rhamnolipid bioaggregates after electromembrane extraction based on an agarose gel using a rotating electrode as a green and organic solvent-free strategy

We here present an efficient approach for the tandem extraction of psychotropic drugs using biodegradable materials. In this regard, gel electromembrane extraction (G-EME) was combined with the emulsification-based microextraction (ME) technique by rhamnolipid bioaggregates as a green extraction approach. The tandem extraction technique consists of two stages: (i) extraction of psychotropic drugs from human urine samples to the acceptor phase situated on the other side of the agarose gel membrane, and (ii) transfer of analytes from the acceptor phase into a colloidal phase of rhamnolipid biosurfactants. The colloidal phase was formed by adding rhamnolipid biosurfactants to the extracted phase of the first step. The colloidal phase was finally injected into a liquid chromatographic system for quantitative analysis. G-EME mechanism is based on electrokinetic migration of charged species toward oppositely charged electrode located in the acceptor solution under the influence of the electric field. After extraction, the analytes were trapped in an emulsion phase floating on the surface of the solution and at the end were injected into the liquid chromatographic system. The method provided good linearity in the ranges of 5-100 and 10-100 μg. L−1 for methamphetamine and amphetamine, respectively with (r2 > 0.992). Also, the detection limits (LODs) were 1 and 5 μg. L−1 for methamphetamine and amphetamine, respectively. The mean extraction recoveries by G-EME-ME for real samples at three spiked concentrations were in the range 95.9-101.1% and complete analytical workflow within only 18 min.

Effect of Aliquat®336 on supported liquid membrane on electromembrane extraction of non-steroidal anti-inflammatory drugs

Up to now, most electromembrane extraction methods describe the use of pure organic solvents or mixtures as supported liquid membrane. However, the need to incorporate carriers in the supported liquid membrane to achieve the extraction of high polar compounds, seems to indicate that the presence of certain additives in the organic solvent may improve the extraction yield. For this reason, some studies have tried to enhance electrokinetic migration in different ways, modifying either the supported liquid membrane or even the donor solution. In this work, it has been studied and optimized an electromembrane extraction of five widely used non-steroidal anti-inflammatory drugs: salicylic acid, ketoprofen, naproxen, diclofenac and ibuprofen. The thickness and porosity of the support, the supported liquid membrane composition, the donor and acceptor phase pH, the voltage, the extraction time and the electrode configuration were optimized. supported liquid membrane was modified by adding different amounts of Aliquat®336, a cationic carrier commonly used in electromembrane extraction procedure for anionic compounds. The results compared with those obtained in the same extraction conditions using the pure organic solvent as supported liquid membrane, showed better extraction recoveries. The highest recoveries were achieved using a pH 5 donor phase and an acceptor phase at pH 12. The recoveries were within the range of 39 and 53% after 12 min extraction, using a voltage of 80 V, a stirring speed of 400 rpm and 1-nonanol modified with Aliquat®336 2.5% (w/v) as support liquid membrane. Detection and quantitation limits were within 0.02–1.0 ng mL−1 and 0.05–3.0 ng mL−1, respectively.The selected analytes were extracted by electromembrane extraction using a home-made device designed with a flat configuration. The analyses were carried out by high performance liquid chromatography with diode array and fluorescence detection and finally, applied to the analysis of human urine samples.

Studies in Electrokinetic Migration Rates of Dyes in Sand and Clay

Abstract Self-designed electrokinetic setups were constructed to examine the differences in electromigration and electroosmotic rates in both sand and clay. Two dyes were analyzed separately to mea...

Size Sorting of Exosomes by Tuning the Thicknesses of the Electric Double Layers on a Micro-Nanofluidic Device.

Exosomes, a type of extracellular vesicle with a diameter of 30–150 nm, perform key biological functions such as intercellular communication. Recently, size sorting of exosomes has received increasing attention in order to clarify the correlation between their size and components. However, such sorting remains extremely difficult. Here, we propose to sort their size by controlling their electrokinetic migration in nanochannels in a micro-nanofluidic device, which is achieved by tuning the thickness of the electric double layers in the nanochannels. This approach was demonstrated experimentally for exosomes smaller than 250 nm. Using different running buffer concentrations (1 × 10−3, 1 × 10−4, and 1 × 10−5 M), most of the exosomes larger than 140, 110, and 80 nm were successfully cut off at the downstream of the nanochannels, respectively. Therefore, it is clarified that the proposed method is applicable for the size sorting of exosomes.

Low permeability zone remediation of trichloroethene via coupling electrokinetic migration with in situ electrochemical hydrodechlorination

To address the challenge of trichloroethene (TCE) remediation in low permeability zone, an inexpensive Cu–Ni bimetallic cathode was proposed in electrokinetic (EK) remediation system to couple electrokinetic migration with in situ electrochemical hydrodechlorination. Aqueous phase TCE was originally added into the anolyte so that breakthrough curves through the low permeability porous soil compartment could be obtained to better understand TCE migration driven by electroosmosis flow using different cathodes. The Cu–Ni cathode resulted in more TCE migration of 7.64 mg compared to that of 5.99 mg with Ni and 4.22 mg with mixed metal oxide (MMO) cathode, suggesting that the Cu–Ni cathode was capable of driving more TCE flux out of the contaminated soil. With the Cu–Ni cathode, 98.4% of TCE flux that reached the cathode was electrochemically reduced on the cathode, which was much higher than that with MMO cathode (77.9%) or Ni cathode (59.6%). TCE mass that was transported by electroosmosis flow increased from 2.04 to 6.68 mg when the voltage gradient increased from 1 to 4 V cm−1, with the normalized energy consumption increasing from 0.06 to 0.16 kWh kg−1 per unit water movement, and from 0.54 to 2.55 kWh g−1 per unit TCE transport. For TCE that did reach the cathode compartment, > 98% degradation maintained at the Cu–Ni cathode with various voltage gradients. The coupled electrokinetic and electrochemical hydrodechlorination technology appears to be a promising strategy for the remediation of low permeability porous media.

Chromium speciation using paper-based analytical devices by direct determination and with electromembrane microextraction

In this study, we developed and compared three different methods for chromium speciation in water samples using microfluidic paper-based analytical devices (μPADs). In all methods, detection was based on the complexation reaction of Cr(VI) with diphenylcarbazide on the μPADs. Cr(III) ions were oxidized to Cr(VI) by Ce(IV) prior to colorimetric detection on the μPADs. In the first method, oxidization of Cr(III) to Cr(VI) in the solution containing both trivalent and hexavalent chromium was performed using a batch procedure to obtain total chromium. A dual electromembrane extraction (DEME) technique for simultaneous preconcentration and extraction of chromium species and a single electromembrane extraction (SEME) for preconcentration and extraction of Cr(VI)/total chromium [quantified as Cr(VI) content after oxidation of Cr(III) ions to Cr(VI)] were used in the second and third methods, respectively. The electromembrane extraction was based on the electrokinetic migration of cationic Cr(III) and anionic Cr(VI) toward the cathode and anode, respectively, into the two different hollow fibres. Octanol-1 and bis(2-ethylhexyl) phosphate (DEHP) in octanol-1 (0.7% v/v) were the most suitable supported liquid membranes for extraction of Cr(VI) and Cr(III), respectively. Among these methods, SEME showed the lowest limits of detection for both analytes.Under optimized conditions, linear calibrations were obtained for Cr(III) from 3 to 30 μg L−1 and for Cr(VI) from 3 to 70 μg L−1. The detection limits were 1.0 μg L−1 and 0.7 μg L−1 for Cr(III) and Cr(VI), respectively. Our developed method was applied to analyse water samples spiked with different concentrations of Cr(III) and Cr(VI) at the parts-per-billion (ppb) level. The statistical evaluation showed that the proposed method agreed well with the validation method, i.e., inductively coupled plasma atomic emission spectroscopy (ICP-AES).

Experimental study on the electrokinetic migration process of Hangzhou sludge

The migration of cations, which leads to the transportation of water molecules, is the essential driving force of electrokinetic dewatering. Several bench-scale experiments on Hangzhou sludge were performed using ferrum, graphite, copper, and aluminum electrodes. The element contents of Na, K, Mg, Ca, Fe, Al, and Cu in the effluent water as well as in the treated soil were measured to investigate the migration process of the corresponding cations. The electrokinetic drainage was noted to have a higher total content of the considered elements compared to that in gravity drainage, which demonstrated that electrokinetic treatment is effective for bound water. In the electrokinetic drainage, the contents of Na and K were much higher than those of other elements. Furthermore, the steady contents of Na and K in the electrokinetic drainage demonstrated the consistent electrokinetic mobility of Na and K ions. Ca and Mg ions tended to precipitate in the cathodic area. Most of the Fe ions generated from the reaction at the anode remained in the anodic area. The extremely low Cu content in the drainage and soil meant that no variations could be observed. Different cations were noted to have different electrokinetic mobilities. Higher electrokinetic mobilities were observed for cations having lower valency or smaller atomic weights. The order of ion electrokinetic mobility was noted to be Na+ > K+ > Mg2+ > Ca2+ > Al3+ > Cu2+ > Fe2+/Fe3+. Therefore, electrokinetic dewatering depends primarily on the presence of cations having a low valency or small atomic weight such as Na, K, Ca, Mg, and Al ions. Fe and Cu ions have low electrokinetic mobility and do not contribute considerably to the transportation of water molecules. The study provided guidance in the application evaluation of the electrokinetic technique in drying various soils.

Joule heating effects in optimized insulator-based dielectrophoretic devices: An interplay between post geometry and temperature rise.

Insulator-based dielectrophoresis (iDEP) is the electrokinetic migration of polarized particles when subjected to a non-uniform electric field generated by the inclusion of insulating structures between two remote electrodes. Electrode spacing is considerable in iDEP systems when compared to electrode-based DEP systems, therefore, iDEP systems require high voltages to achieve efficient particle manipulation. A consequence of this is the temperature increase within the channel due to Joule heating effects, which, in some cases, can be detrimental when manipulating biological samples. This work presents an experimental and modeling study on the increase in temperature inside iDEP devices. For this, we studied seven distinct channel designs that mainly differ from each other in their post array characteristics: post shape, post size and spacing between posts. Experimental results obtained using a custom-built copper Resistance Temperature Detector, based on resistance changes, show that the influence of the insulators produces a difference in temperature rise of approximately 4°C between the designs studied. Furthermore, a 3D COMSOL model is also introduced to evaluate heat generation and dissipation, which is in good agreement with the experiments. The model allowed relating the difference in average temperature for the geometries under study to the electric resistance posed by the post array in each design.

Electromembrane extraction-looking into the future.

Analytical microextraction techniques, including solid-phase microextraction (SPME) Arthur & Pawliszyn (Anal Chem 62:2145-2148, 1990), stir bar sorptive extraction (SBSE), Baltussen et al. (J Microcol 11:737-747, 1999), single-drop microextraction (SDME) Jeannot & Cantwell (Anal Chem 68:2236-2240, 1996), hollow-fiber liquid-phase microextraction (HF-LPME) Pedersen-Bjergaard & Rasmussen (Anal Chem 71:2650-2656, 1999), dispersive liquid-liquid microextraction (DLLME) Berijani et al (J Chromatogr A. 1123:1-9, 2006), and electromembrane extraction (EME) Pedersen-Bjergaard & Rasmussen (J Chromatogr A 1109:183-190, 2006) have gained considerable interest in recent years. The latter technique, EME, differs from the others by the fact that mass transfer and extraction is facilitated by electrokinetic migration. Thus, basic or acidic analytes are extracted in their ionized form from aqueous sample, through an organic supported liquid membrane (SLM) and into an aqueous acceptor solution under the influence of an electrical potential. EME provides pre-concentration and sample clean-up, and can be performed in 96-well format using only a few microliter organic solvent per sample (green chemistry). Extraction selectivity is controlled by the direction and magnitude of the electrical field, by the chemical composition of the SLM, and by pH in the acceptor solution and sample. This trends article discusses briefly the principle, performance, and current status of EME, and from this future directions and perspectives are identified. Unlike traditional extraction methods, EME involves electrokinetic transfer of charged analyte molecules across an organic phase (SLM) immiscible with water. This process is still not fully characterized from a fundamental point of view, and more research in this area is expected in the near future. From author's point of view, such research at the interface between electrophoresis and partition will be highly important for future implementation of EME. Graphical abstract ᅟ.

NOM fouling resistance in response to electric field during electro-ultrafiltration: Significance of molecular polarity and weight

Electro-ultrafiltration is an effective method for mitigating membrane fouling. Herein, anti-fouling mechanisms for the electro-ultrafiltration of natural organic matter (NOM) were investigated to illuminate the significance of NOM molecular polarity and weight. Results indicated that the membrane flux of NOM electro-ultrafiltration was greatly enhanced by electric field (EF) application, and that the increase in membrane flux magnitude for electro-ultrafiltration was more pronounced for NOM with higher hydrophilicity and larger molecular weight. The electro-ultrafiltration flux of the hydrophilic substances in NOM was enhanced by up to 20% after applying the voltage. The enhancement of membrane flux was more prominent for the electro-ultrafiltration of humic acid (HA) solution with high ionic strength and coexisting Ca2+. With increasing EF strength in the electro-ultrafiltration of HA, membrane flux increased at first due to the electrokinetic migration of negatively charged HA, and then declined for fields larger than the critical EF, where electro-ultrafiltration reached maximum flux. The HA molecules became polarized under a high EF, which induced aggregation between the molecules and increased affinity between HA and the membrane. This facilitated the formation of a dense cake layer, leading to relatively severe membrane fouling under EF strengths larger than the critical EF.

Electromembrane extraction of substances with weakly basic properties: a fundamental study with benzodiazepines.

Electromembrane extraction (EME) of weakly basic benzodiazepines was investigated (-1.47<pKa<5.01). 96-well EME was performed with strongly acidic conditions in the acceptor solution using 250-mM trifluoroacetic acid to maximize ionization. Recoveries more than 80% were obtained for analytes with pKa > 2, whereas EME was less efficient for substances with pKa<2. The latter was trapped in the supported liquid membrane due to less acidic pH conditions in the acceptor solution close to the supported liquid membrane. EME followed by UHPLC-MS/MS analysis was evaluated from human plasma, and the results were in compliance with EMA guidelines.Both electrokinetic migration and passive diffusion contributed to mass transfer when performing EME of weakly basic analytes.

Selective Determination of Chromium(VI) in Industrial Wastewater Samples by Micro-Electromembrane Extraction Combined with Electrothermal Atomic Absorption Spectrometry

This study describes application of free liquid membrane (FLM) in micro-electromembrane extraction (μ-EME) of Cr(VI) from wastewater samples. Amount of Cr(VI) was quantified by electrothermal atomic absorption spectrometry. The transportation of Cr(VI) across the FLM was explored by electrokinetic migration and ion-exchange process. FLM and acceptor solution types, pH of donor and acceptor solutions, applied electrical potential, as well as FLM thickness were optimized. Presence of an anion exchange carrier (methyl trialkyl-ammonium chloride, Aliquat 336) in FLM facilitated Cr(VI) transportation. The best performance was observed for 1-octanol (containing 5% Aliquat 336) with thickness of 1 mm used as FLM, under applied electrical potential of 75 V, when 0.5 M NaClO4 and 0.1 M HCl were used as the acceptor and donor phases, respectively; and the extraction time was set to 5 min. Linearity was obtained in the working range of 0.5–14.0 ng mL−1 Cr(VI) (R2 > 0.98). The calculated limit of detection was below 0.06 ng mL−1. Application of this method to wastewater samples showed that relative recoveries of the spiked Cr(VI) in the samples were in the range of 73.8–85.1%, based on the standard addition method.

Electroosmotic Flow Dispersion of Large Molecules in Electrokinetic Migration.

It is a common knowledge that large molecules have small diffusion coefficients. Therefore, it was thought that these molecules should generate very narrow peaks in electropherograms, because longitudinal diffusion was thought to be the only factor that contributes to band broadening in electrophoretic separation systems in capillaries and microfluidics. However, it is also common to observe that large molecules such as proteins and polymers often produce wider peaks than most small molecules. It is demonstrated in this work that dispersion of analytes during electrokinetic migration is also the results of Taylor dispersion. Similar to conventional Taylor dispersion, peak broadening is more pronounced for particles with smaller diffusion coefficients. The theoretical description of band broadening caused by electroosmotic flow dispersion (EOFD) and the experimental verification of this phenomenon are presented in this paper. The dispersion of various sized molecules, from small peptides to large proteins, in capillary electrophoresis is used as examples in this study.