On-line coupling of microdialysis sampling with microchip-based capillary electrophoresis

Microdialysis sampling is a technique that has been used for in vivo and in vitro monitoring of compounds of pharmaceutical, biomedical, and environmental interest. The coupling of a commercially available microdialysis probe to a microchip-based capillary electrophoresis (CE) system is described. A continuously flowing dialysate stream from a microdialysis probe was introduced into the microchip, and discrete injections were achieved using a valveless gating approach. The effect of the applied voltage and microdialysis flow rate on device performance was investigated. It was found that the peak area varied linearly with the applied voltage. Higher voltages led to lower peak response but faster separations. Perfusion flow rates of 0.8 and 1.0 microL/min were found to provide optimal performance. The on-line microdialysis/microchip CE system was used to monitor the hydrolysis of fluorescein mono-beta-d-galactopyranoside (FMG) by beta-d-galactosidase. A decrease of the FMG substrate with an increase in the fluorescein product was observed. The temporal resolution of the device, which is dependent on the CE separation time, was 30 s. To the best of our knowledge, this is the first reported coupling of a microdialysis sampling probe to a microchip capillary electrophoresis device.