SPATIAL AND TEMPORAL DEPLETION OF IONS FROM NONCROSSLINKED DENATURINGPOLYACRYLAMIDE IN CAPILLARY ELECTROPHORESIS

Electrical conductivity across a polyacrylamide-filled capillary decre ases during the separation of DNA sequencing fragments. This conductiv ity decrease is localized to the first few centimeters at the injectio n (negative) end of the capillary; no conductivity change is noted at the detection (positive) end of the capillary. The zone of decreased c onductivity extends further into the capillary as the separation proce eds. The zone is most important for freshly prepared capillaries; capi llaries used nine days after polymerization generate an insignificant current drop. The data are consistent with ionic depletion due to diff erences in transport numbers between the separation medium and the buf fer reservoirs.