Measurements of the shape of electrophoretic bands of phycoerythrin and conalbumin have been made at regular intervals during migration in agarose gels. Analysis of the peak shapes suggests the existence of a significant degree of asymmetry. This is to be contrasted with the symmetry around the peak associated with the generally assumed Gaussian band. The degree of asymmetry of the bands decreased as a function of time and increased with agarose concentration. A similar experiment on DNA indicated constancy of the degree of asymmetry as a function of time. These results can be interpreted as, but do not prove the validity of, a nonlocal diffusion equation which generalizes a theory originally put forth by Giddings and Eyring (J. Am. Chem. Soc. 1955, 59, 416-420). The results may be significant in framing a measure of the resolvability of electrophoretic peaks.

DNA of approximately 2 kbp in length was previously found not to diffuse significantly in 1-1.5% agarose gels in the absence of an electric field, but to disperse during electrophoresis (Yarmola, E., Chrambach, A., Electrophoresis 1995, 16, 345-349). Accordingly, a process distinct from diffusion, and responsible for band spreading with migration time in gel electrophoresis, was defined as dispersion. Correspondingly, the diffusion coefficient, D(diff), was distinguished from a dispersion coefficient, D(disp). For DNA of approximately 1, 2 and 3 kbp, D(diff) and D(disp) were measured in agarose gel electrophoresis (1.0% SeaKem GTG). In that order of DNA length, D(disp)/D(diff) was found to increase from 5 to 15 to 45, showing that with increasing DNA length, time-dependent band spreading, and thus resolution in gel electrophoresis, is governed predominantly by dispersion, not diffusion. It is assumed that the essential part of electrophoretic dispersion is due to entanglement of the DNA molecule in the gel. Indirect evidence for such an entanglement derives from the observation of peak asymmetry and its interpretation by the Giddings-Weiss model.

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