CAPILLARY ELECTROPHORESIS OF DNA IN UNCROSS-LINKED POLYMER-SOLUTIONS

We have used dilute and semi-dilute uncross-linked hydroxyethyl cellul ose (HEC) solutions as separation matrices for capillary electrophores is of DNA restriction fragments. In these experiments, we investigated the effects of HEC molecular weight(star) and concentration on resolu tion, attempting to relate these parameters to the polymer entanglemen t threshold concentration. The entanglement thresholds of seven molecu lar weight fractions of hydroxyethyl cellulose were determined from vi scosity-concentration data; the entanglement threshold was found to sc ale as N--1,N-2, where N = number of HEC monomers. This finding is not in agreement with classical scaling arguments. We present a relations hip to predict the observed entanglement threshold of HEC in solution as a function of number average molecular weight. It was found that ex cellent separation of Phi X174/HaeIII DNA restriction fragments (72-13 53 base pairs) by capillary electrophoresis in HEC solutions can be ac hieved significantly below the entanglement threshold, depending on DN A size and HEC molecular weight. The mechanism of separation in these uncross-linked polymer solutions must therefore be reexamined. Our exp eriments show that the entanglement threshold is a useful parameter in predicting a range of HEC concentrations which will separate certain DNA fragments for a given HEC molecular weight. However, the presence of a fully entangled network is not a prerequisite for separation.