Step change of counterion--a new option in capillary zone electrophoresis

In contrast to common capillary zone electrophoresis, with a constant composition of the background electrolyte, a new method is described, based on a change of the ionic matrix composition during the migration of the sample components. The proposed method expands the scale of pK's of analyzed compounds in a single run and affords new potential for optimizing the separation. The step change of the ionic matrix composition was achieved by displacing the primary matrix by the modified ionic matrix (electrolyte) which migrated against the movement of the sample components. The separation thus proceeded in the primary ionic matrix (electrolyte) while the detection was performed in the modified matrix with resultant shortening of the analysis time and convenient quantitation. A model mixture of five compounds, with a difference of four units in pK could be well resolved.