Microdialysis sampling and high-performance liquid chromatography with chemiluminescence detection for in-vivo on-line determination and study of the pharmacokinetics of levodopa in blood.

A simple, reliable, and reproducible method for in-vivo on-line separation and determination of levodopa has been based on microdialysis then high-performance liquid chromatography with chemiluminescence detection. The perfusate is perfused at a flow rate of 5 microL min(-1). The concentration of levodopa in the dialysate is determined on line with a chemiluminescence system. The dialysate sample volume is approximately 20 microL. The response of the system is linearly related to the concentration of levodopa in the range 1 x 10(-8) to 1 x 10(-6) g mL(-1) (r2 = 0.9995) with a detection limit (3sigma) of 3 x 10(-9) g mL(-1) and sample throughput of 12 h(-1); RSD is 2.8% (n = 11). The method has been successfully used to study the pharmacokinetics of levodopa in vivo; the values of the pharmacokinetics parameters Cmax, AUC(0-t) and Tmax were 16.60, 20.92 ng mL(-1), and 90 min, respectively.