Size-dependent separation of proteins in the presence of sodium dodecyl sulfate and dextran in capillary electrophoresis: effect of molecular weight of dextran.

Dextran solutions are widely used as sieving medium in protein analysis by capillary electrophoresis in the presence of sodium dodecyl sulfate. We studied the effect of dextran molecular weight on the separation efficiency using different dextran preparations with wide and very narrow molecular weight distributions, in the range between 1270 and 2,000,000. Migration times and band broadening of proteins were significantly affected by the molecular weight of dextran. Migration times of proteins decreased as molecular weights of the dextrans decreased. Satisfactory separation of all the proteins was possible with all dextrans except those with molecular weights of 70,000 and 23,800 where bovine serum albumin and phosphorylase b failed to be separated. Unexpectedly rapid separation of all the proteins with enhanced resolution could be observed using two dextrans with a narrow molecular weight distribution, with molecular weights of 1270 and 5220. Clearly the use of dextran with higher molecular weight is not the only way to achieve efficient separation of proteins. The separation mechanism in the presence of the low molecular weight dextrans remains to be made clear in a future study.