Crossed-field electrophoresis

Fig.12 Schematic of the motion of a large DNA molecule during crossed field electrophoresis, (a) For long switching times the...

VI.2 Computer Simulations of Crossed Field Electrophoresis We have studied crossed field electrophoresis using a computer simulation of the BRM . Fig. 13 shows a diagram of the mobility p/p vs pulse duration for 6 different molecular sizes, 4 of them having a size-independent plateau mobility p/pQ= Pp/Po continuous fields. 

Fig.13. Southern et al.54 proposed a theory of crossed-field electrophoresis according to which the mobility should be very small for t

Crossed-field electrophoresis provides an interesting alternative to intermittent-field electrophoresis. The idea is simply to change by 90 the direction of the field each time the tube is fully oriented in the field direction because we know that this orientation destroys the molecular-size dependence of the electrophoretic velocity. Although some intra-tube effects can be expected to play a role here, especially because crossed fields may induce the creation of a large number of transverse tube leakages, the BRM reproduces most experimentally observed effects up... 

Boyd, BM Prausnitz, JM Blanch, HW, High-Frequency Altemating-Cross-Field Gel Electrophoresis with Neutral or Shghtly Charged Interpenetrating Networks to Improve DNA Separation, Electrophoresis 19, 3137, 1998. 

Figure 27-36. Crossed field pulsed electrophoresis. (Courtesy Chrambach, A., Dunn, M.J., Radola, B.J., Eds. Advances in Electrophoresis Vol I VCH Press, Weinheim, Germany, 1987)...

The silica crystal array can also be used for pulsed fields by adding two additional reservoirs to the PDMS cover to create a 120° crossed field. The mobility of different size long DNA (48.5, 23.1, and 9.4 kbp) vary in the pulsed-field array, indicating that they could be separated in such an array if a suitable injection system were employed. The high electric fields and rapid pulse times employed in these experiments are comparable to pulsed-field electrophoresis in the DNA prism pillar array [37]. 

As we will see in the next section, when field-inversion electrophoresis is used to separate nucleic acids in certain size ranges, intra-tube relaxation effects take place. Of course, as the angle between the two fields increases from 90 to 180 , we expect that the crossed field effects discussed earlier will be modified by more and more of the intra-tube effects that sometimes dominate in field-inversion electrophoresis. It is not the goal of this article to discuss the angles between 90 to 180 . The next section presents a discussion of field-inversion electrophoresis as well as the ways to optimize the reorientation-induced separation obtained with this experimental arrangement. 

The biased reptation model provides a good framework to discuss the experimental results of the various gel electrophoresis techniques used to separate nucleic acids. Although more experiments are needed to fully characterize these techniques, available results indicate that the simplified version of the model discussed in this paper is satisfactory when low-frequency pulsed fields are used, or when transient intra-tube effects are not dominant. This is the case in continuous fields, for small molecules in intermittent fields, and possibly also for crossed fields. However, intra-tube effects are observed to play a role in field-inversion electrophoresis, for long molecules in intermittent fields, and during the first stages of an experiment (where an orientation overshoot is observed). 

Theory Cross-flow-electrofiltration can theoretically be treated as if it were cross-flow filtration with superimposed electrical effects. These electrical effects include electroosmosis in the filter medium and cake and electrophoresis of the particles in the slurry. The addition of the applied electric field can, nowever, result in some qualitative differences in permeate-flux-parameter dependences. 

Heiger, D. N., Cohen, A. S., Aharon, S., and Karger, B. L., Separation of DNA restriction fragments by high performance capillary electrophoresis with low and zero cross-linked polyacrylamide using continuous and pulsed electric fields,. Chromatogr., 516, 33, 1990. 

A modified technique consisting of an electric field applied perpendicular to a flowing buffer solution and using chromatography paper as support(cross-electrophoresis) has been exploited to study the reaction of neomycin with heparin 9 184. Evidence for the formation of a neomycin-heparin complex was obtained by this means. 

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