On-line monitoring of electroosmotic flow for capillary electrophoretic separations

A recently developed technique for monitoring electroosmotic flow (EOF) in capillary electrophoresis by periodic photobleaching of a neutral fluoropho re added to the running buffer has been further characterized and optimized and then applied to monitoring EOF during a typical capillary electrophore sis separation. The concentration of neutral fluorophore (rhodamine B) adde d to the running buffer for monitoring EOF has been decreased by one order of magnitude. The rate at which EOF can be measured has been increased from 0.2 to 1.0 Hz by decreasing the distance between the bleaching beam and th e laser-induced fluorescence detector from 6.13 to 0.635 mm. The precision of the measured EOF ranges from 0.2 to 1.8%. Under typical experimental con ditions. the dynamic range for flow measurements is 0.066 to 0.73 cm. s(-1) . Experimental factors affecting precision, signal-to-noise (SIN) ratio and dynamic range for EOF monitoring have been examined. This technique has be en applied to measure EOF during a separation of phenolic acids with analyt e detection by UV/VIS absorbance. The EOF monitoring method has been shown not to interfere with UV/VIS absorbance detection of analytes.