CHANGE IN CONDUCTIVITY IN NON-CROSS-LINKED POLYACRYLAMIDE CAPILLARY ELECTROPHORESIS - EFFECTS OF AGING POLYACRYLAMIDE AND BUFFER COMPOSITION

Upon application of an electric field to a polymer-filled capillary, t here is a rapid expulsion of excess ions associated with the polymeriz ation mixture. This expulsion is complete in about 10-15 min. A much s lower transport of ions occurs at one end of the capillary; the transp ort arises because of the difference in transference number between th e buffer reservoir and the polymer filled capillary. This ionic transp ort leads to a change in the conductivity of the polymer at one end of the capillary. We have monitored the conductivity profile in 5% T non -cross-linked polyacrylamide capillaries at 300 V/cm for different age s of polyacrylamide. The profile was fit with a double-exponential, co rresponding to the rapid expulsion of reaction ions and the slow trans port of ions due to differences in transference number. The fit indica tes that there are more ions in polyacrylamide as it is aging, and tha t the depletion of ionic concentrations is less important in aged poly acrylamide than in fresh polyacrylamide. The effect of the buffer comp osition was studied. By changing from 1XTBE buffer reservoirs to a mix ture of 30 mM KCl and 1XTB buffer, the depletion of ionic concentratio n at the injection end disappears and is replaced by an increase of io nic concentration at the ground end. By changing 1XTBE buffer reservoi rs to 1XTBE, 5% T non-cross-linked polyacrylamide and seven molar urea buffer reservoirs the depletion of ionic concentration at the injecti on end disappears.