Semi-automated high-performance liquid chromatographic method for the determination of cyclosporine in plasma and blood using column switching.

A sensitive, semi-automated high-performance liquid chromatographic method utilizing column switching is described for the determination of cyclosporine in plasma and blood. This method involves a short and improved manual protein precipitation of the sample followed by an automated clean-up of the supernatant. After automatic loading of the clean supernatant onto an LC-8 column for initial separation, the segment containing cyclosporine is loaded (automatically) onto an LC-18 column for final separation and quantitation. Cyclosporine is detected by its ultraviolet absorption at 202 nm. The rate of analysis was four samples per h running 24 h per day (ca. 100 samples per day). The method is sensitive enough to measure with confidence cyclosporine concentrations of 8 microgram/l in plasma and 20 microgram/l in blood with a linear response up to 2500 microgram/l using only 0.5 ml of sample. No internal standard is required. The method was applied continuously (24 h per day) to approximately 1000 samples without deterioration in method parameters.