Sweeping on a microchip: Concentration profiles of the focused zone in micellar electrokinetic chromatography

On-line sample concentration by sweeping was investigated in microchip mice llar electrokinetic chromatography (MEKC), By changing the distance between the injection cross and the detection points, the profile of the concentra tion process and the diffusion process in sweeping was elucidated. Rhodamin e B injected for 4 s was best concentrated by sweeping at 9.4 mm from the i njection cross and the enhancement factor was 450. At the longer distance f rom this point the peak of Rhodamine B was broadened and diluted by diffusi on. The diffusion constant of Rhodamine B calculated from the experiment wa s 5.7 x 10(-6) cm(2)s(-1). The mixture of rhodamine B, sulforhodamine B, an d cresyl fast violet was concentrated by sweeping and separated by MEKC at the same time.