Intermittent field electrophoresis

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... 

Field-inversion electrophoresis is predicted to give a much better spreading of the bands. The idea here is to use a secondary, weaker negative field to speed up the relaxation of the reptation tube between the primary (forward) electrophoretic pulses. This is therefore similar to intermittent field electrophoresis, where a secondary field instead of Brownian motion is used to decrease the tube orientation. By choosing the field and time ratios and properly, one can optimize the band... 

Therefore, in order to be successful, an intermittent field gel electrophoresis has to use the conditions (with the size of the... 

Figure 11 shows the result of a computer simulation of intermittent-field gel electrophoresis with 0=1.0. If only molecules with 2continuous field since case. However, if larger molecules are present,... 

VII. 4 Conclusion In conclusion, the BRM predicts that field-inversion gel electrophoresis should improve the separation of "plateau molecules if two unequal fields are used. In this case, the reverse field, which is of lesser intensity, serves to reduce the orientation of the reptation tube since this is field-induced, this is much faster than the tube relaxation process which is the basis of the intermittent-field technique. Experimentally, this reptation induced effect has been observed, but a potentially even more powerful "resonance- ike effect has been observed to exist as well. This latter effect leads to band-inversion however, and since it occurs for pulse durations t =x (N)involves chain movements inside its tube and/or movements of only parts of the tube, which have not been discussed in this article. 

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). 

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