SYSTEM PEAKS AND DISTURBANCES TO THE BASE-LINE UV SIGNAL IN CAPILLARYZONE ELECTROPHORESIS

Non-steady-state processes in capillary electrophoresis can be estimat ed by applying a steady-state mathematical model. Calculations with a steady-state model indicate that in capillary electrophoresis, moving boundary zones can originate from discontinuities in the concentration of the co-ions and/or the pH of the background electrolyte. Calculati ons showed that cationic moving boundaries with high mobilities origin ate with low system pH values. If the separation capillary and anode c ompartment are filled with electrolytes, different in concentration or pH, a shift of the baseline UV signal can occur. Block-shaped discont inuities in pH and/or concentrations split up in a migrating part with a mobility determined by the composition of the background electrolyt e and a part migrating with the velocity of the electroosmotic flow at the position of the original disturbance. As a result, dips of the el ectroosmotic flow marker (low background concentration) split up and a negative system peak migrates through the system at low system pH val ues. Injections of high concentrations of background electrolyte or sa mples at high ionic strength lead to positive system peaks. These syst em peaks are, of course, only visible if the background electrolyte sh ows UV-absorbing properties. Experimentally determined data match the calculated values for these mobilities and baseline shifts.