When the viscosity of your CZE method changes, the following can be expected. Changing anyone of these parameters in CZE can reduce your coefficient of variation therefore it is important to control your viscosity accurately.
Electro Osmotic Flow (EOF): A lower viscosity will increase the EOF in your CZE method.
Analyte to Wall Interaction: A non-homogeneous viscosity will cause analyte to wall effects that can result in non-reproducible migration times and Peak Tailing.
Electrophoretic Mobility: A decrease in viscosity can cause an increase in electrophoretic mobility