Anal. Chem. 1995, 67, 3234-3245

Electroosmotically Transported Baseline Perturbations in Capillary Electrophoresis

Christa L. Colyer,+Keith B. Oldham,* and Artjom V. Sokirko

Department of Chemistry, Trent University, Peterborough, Ontario K9J 7B8, Canada

Two anomalous capillary electrophoresis (CE) phenomena, referred to as the baseline shift and spontaneousmarker peak, are investigated. The baseline shift and spontaneous-marker peak have been observed in a simple CE system with no sample injection and no deliberately formed concentration boundaries, a sodium benzoate solution as the running electrolyte, and on-column UV absorbance detection. The baseline perturbations, which are believed to have physical origins at the capillary inlet, are transported along the capillary at the rate of electroosmotic flow. Baseline perturbations observed previously have been attributed to pH changes or temperature changes, and although the latter may influence our results somewhat, neither of these effects can explain the phenomena that we have observed. Instead, we believe these baseline shifts and spontaneous-marker peaks are attributable to changes in the actual concentration of the running electrolyte. Although the property of a capillary end which is responsible for the generation of baseline perturbations remains unknown, the transport of the concentration excursions and the origin of spontaneousmarker peaks are explained.