Continuous fast focusing in a trapezoidal void channel based on bidirectional isotachophoresis in a wide pH range

Evolution of the theoretical description of the isoelectric focusing experiment: II. An open system isoelectric focusing experiment is a transient, bidirectional isotachophoretic experiment

The carrier ampholytes-based (CA-based) isoelectric focusing (IEF) experiment evolved from Svensson's closed system IEF (constant spatial current density, absence of convective mixing, counter-balancing electrophoretic and diffusive fluxes yielding a steady state pH gradient) to the contemporary open system IEF (absence of convective mixing, large cross-sectional area electrode vessels, lack of counter-balancing electrophoretic- and diffusive fluxes leading to transient pH gradients). Open system IEF currently is described by a two-stage model: In the first stage, a rapid IEF process forms the pH gradient which, in the second stage, is slowly degraded by isotachophoretic processes that move the most acidic and most basic CAs into the electrode vessels. An analysis of the effective mobilities and the effective mobility to conductivity ratios of the anolyte, catholyte, and the CAs indicates that in open system IEF experiments a single process, transient bidirectional isotachophoresis (tbdITP) operates from the moment current is turned on until it is turned off. In tbdITP, the anolyte and catholyte provide the leading ions and the pI 7 CA or the reactive boundary of the counter-migrating H₃ O⁺ and OH^- ions serves as the shared terminator. The outcome of the tbdITP process is determined by the ionic mobilities, pK_a values, and loaded amounts of all ionic and ionizable components: It is constrained by both the transmitted amount of charge and the migration space available for the leading ions. tbdITP and the resulting pH gradient can never reach steady state with respect to the spatial coordinate of the separation channel.

Preparative separation of immunoglobulins from bovine colostrum by continuous divergent-flow electrophoresis

Immunoglobulins in bovine colostrum were separated and fractionated from other proteins using the method and instrumentation developed in our laboratory. The proposed separation was based on bidirectional isotachophoresis/moving boundary electrophoresis with electrofocusing of the analytes in a pH gradient from 3.9 to 10.1. The preparative instrumentation included the trapezoidal non-woven fabric that served as separation space with divergent continuous flow. The defatted and casein precipitate-free colostrum supernatant was loaded directly into the instrument without any additional colostrum pre-preparation. Immunoglobulin G was fractionated from other immune proteins such as bovine serum albumin, β-lactoglobulin, and α-lactalbumin, and was continuously collected in separated fractions over 3 h. The fractions were further processed, and isolated immunoglobulin G in the liquid fractions was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by re-focusing in gel isoelectric focusing. Separated immunoglobulin G was detected in seven fractions by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a gradually decreased concentration in the fractions. Re-focusing of the proteins in the fractions by gel isoelectric focusing revealed multiple separated zones of immunoglobulin G with the isoelectric point values covering the range from 5.4 to 7.2. Each fraction contained distinct zones with gradually increased isoelectric point values and decreased concentrations from fraction to fraction.

Preparative continuous flow electrophoretic instrumentation for purification of biological samples

We constructed preparative instrumentation and developed the method that are based on separation of the samples by bidirectional isotachophoresis/moving boundary electrophoresis in continuous divergent flow. The described instrumentation can be used for variety of the samples, however, it can be easily optimized and tailored for the specific sample. The trapezoid separation bed from non-woven textile exhibited minimum adsorption effect for sample and it can be used repeatedly. By addition of different spacers via separation space inlets, the sections of pH gradient can be modified to enhance the separation. The liquid flow from two inlets positioned on each side of the sample inlet prevented the contact of the sample with anolyte and catholyte at the analysis beginning. One pair of thin electrodes (graphite and stainless-steel) was placed at the separation space output. The electrode products were washed out into drains without disturbing the focusing process. The influence of EOF was managed by tilting the separation bed in direction from cathodic to anodic side. The components of spirulina supernatant and color pI markers were separated in the pH gradient from 3.9 to 10.1. pH gradient was stable for at least 4.5 hours and spirulina supernatant from about 0.12 g of dry powder was processed. Compared to other preparative methods used for spirulina separation, the presented method/instrumentation working with continuous divergent flow had essential advantages. The efficient separation was fast, and no intermediate steps were necessary to obtain liquid fractions with separated components compatible with further biological experiments. This article is protected by copyright. All rights reserved.

DNA purification and concentration by isotachophoresis in nonwoven fabric strip

We present a novel method for concentration and purification of DNA from biological samples. The method is based on isotachophoretic separation of DNA strands in a separation bed made of a disposable nonwoven fabric strip. Application of oxalate as the leading ion prevented corrosion of the carbon anode and also the leading ion was continually removed from the system due to its decomposition into CO₂ at the anode. The fractions were marked by three colored markers of electrophoretic mobility closely surrounding the mobility of DNA. The fraction collection was realized by a centrifugal drain of cut out strip segments. The method was evaluated using two purified salmon sperm DNA fragments of lengths 200 bp and 2000 bp. The results confirmed the high DNA concentrating effect of the method (34-fold increase of the original DNA concentration). The composition of running solutions and voltage program were optimized in order to finish the analysis within 30 min. The optimized method was used to extract, concentrate and purify DNA from a crude yeast cell lysate. The maximum DNA enrichment factor decreased to 12 due to the stretching of DNA zones caused by low-molecular contaminants present in the original lysate. The average recovery determined for yeast DNA was 71 ± 11% (n = 3). The connected elimination of the proteins from DNA zones resulted in the purification factor value of 582 for DNA vs proteins. This demonstrates that the presented method is capable to concentrate DNA from the bulk volume and to further purify it from crude cell lysates using a simple instrumentation and low-cost disposable separation bed.

Continuous flow electrophoretic separation - Recent developments and applications to biological sample analysis

Continuous flow electrophoretic separation with continuous sample loading provides the advantage of processing volumes of any sizes, as well as the benefit of a real-time monitoring and optimization of the separation process. In addition, the spatial separation of the sample enables collecting multiple separated components simultaneously and in a continuous manner. The separation is usually performed in mild buffers without organic solvents and detergents (sample biological activity is retained) and it is carried out without usage of a solid support in the separation space preventing the interaction of the sample with it (high sample recovery). The method is used for the separation of proteins/peptides in proteomic applications, and its great applicability is to the separation of the cells, cellular organelles, vesicles, membrane fragments, and DNA. This review focuses on the electrophoretic separation performed in a continuous flow and it describes various electrophoretic modes and instrumental setups. Recent developments in methodology and instrumentation, the integration with other techniques, and the application to the biological sample analysis are discussed as well.