Displacement electrophoresis

Hjerten, S., Elenbring, K., Kilar, F., Liao, J.-L, Chen, A. J. C., Siebert, C. J., and Zhu, M.-D., Carrier-free zone electrophoresis, displacement electrophoresis and isoelectric focusing in a high-performance electrophoresis apparatus, /. Chromatogr., 403, 47, 1987. 

Isotachophoresis. In isotachophoresis (ITP), or displacement electrophoresis or multizonal electrophoresis, the sample is inserted between two different buffers (electrolytes) without electroosmotic flow. The electrolytes are chosen so that one (the leading electrolyte) has a higher mobility and the other (the trailing electrolyte) has a lower mobility than the sample ions. An electric field is applied and the ions start to migrate towards the anode (anions) or cathode (cations). The ions separate into zones (bands) determined by their mobilities, after which each band migrates at a steady-state velocity and steady-state stacking of bands is achieved. Note that in ITP, unlike ZE, there is no electroosmotic flow and cations and anions cannot be separated simultaneously. Reference 26 provides a recent example of capillary isotachophoresis/zone electrophoresis coupled with nanoflow ESI-MS. 

CE is a family of techniques similar to those found in conventional electrophoresis zone electrophoresis, displacement electrophoresis, isoelectric focusing (IEF), and sieving separations. Other modes of operation unique to CE include micellar electrokinetic chromatography (MEKC) and capillary electrochromatography (CEC). 

Clear distinction between Epacked, E0pen and E is of particular importance when accurate knowledge of the electric field strength is required for evaluation of the electroosmotic and electrophoretic mobilities from the observed migration times. Similar situation arises in other systems that are subject to similar conservation principles, e.g., displacement electrophoresis. 

M.-D. "Carrier-free zone electrophoresis, displacement electrophoresis and isoelectric focusing in a high-performance electrophoresis apparatus" /. Chromatography. 1987, 403, pp 47-61. 

Development of the technique was slow until the early 1960s, when suitable apparatus became commercially available. Several names have been used for this separation technique ion migration method, moving boundary method, displacement electrophoresis, and cons electrophoresis. The term used here, isotachophoresis (ITP), is based on the important associated phenomenon of the identical velocities of the sample zones in the steady state. 

Isotachophoresis (displacement electrophoresis) belongs to one of the four basic electrophoretic separation techniques Moving boundary electrophoresis, zone electrophoresis and Isoelectric focusing. 

From 1964-1974 A.J.P. Martin has been nominated as extraordinary professor at the Eindhoven University on the chair entitled The theory of Analogues", in these days he started, together with F.H. Everaerts, a project called Displacement electrophoresis", later-on called Isotachophoresis [3]. 

The world of electromigration separations is sharply divided into two areas. Zone electrophoresis on paper and related procedures have (in spite of their wide applicability to diverse organic compounds) already passed their period of favour. The other branch is represented by the more recent techniques some of which have already became widely accepted (such as isoelectric focusing or separations in polyacrylamide gel) and the others that are at the moment in the centre of a rapid development like displacement electrophoresis (isotachophoresis). This chapter is devoted mainly to analytical procedures such as these which are governing the area of electromigration separations at the moment with a single exception flow deviation (curtain) electrophoresis which will be discussed in more detail because it offers several new dimensions in the separation field. The other preparative procedures are summarized only briefly. 

Martin and Everaerts published a paper in 1967 which gave a new impulse. Their capillary equipment for displacement electrophoresis had already the character of the present devices. They used as a detector a thermocouple glued on the outside wall of a thin-walled separation capillary. The principle of and the equipment for the moving boundary analysis with a detection performed potentio-metrically was reported by Hello in 1968. One year later, Fredriksson developed the analytical apparatus for the displacement electrophoresis . He used a conductivity detector, successfully separated low-molecular fatty acids and performed quantitative an dyses by measuring the lengths of zones. 

A more extensive study on the displacement electrophoresis was reported by Martin and Everaerts in 1970. In this study they covered substantial parts of the theory, the instrumentation and the application of this technique. The year 1970 is a certain milestone in the nomenclature since the name isotachophoresis was then introduced and adopted (cf. ). 

ITP, also known as displacement electrophoresis, was first performed in capillary tubes by Ever-aerts et al. [69] for the separation of strong anions using a thermocouple detector. Since then, ITP has been used for the analysis of various important chemical and biological species such as amino acids [70], peptides [71], nucleotides [72], proteins [73,74], heavy metal ions [75], and other organic/inorganic ions [76,77] on a variety of detection platforms such as UV absorbance, conductivity and fluorescence detection. Over the past 15 years, ITP has been used as a preconcentration technique in conjunction with CE [78]. This mode of ITP, referred to as transient isotachophoresis (tITP), has been implemented on microchip platform in the recent years to achieve improved sensitivity [22,79,80]. 

As a separation techique, isotachophoresis (ITP also known as displacement electrophoresis) resolves analytes as contiguous zones which migrate in order of mobility. The sample is injected into the capillary between a leading buffer (with ion mobility greater than that of all analytes) and a terminating buffer (with ion mobility less than that of all analytes). Zones migrate at equal veloc-... 

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