Abstract
An automated determination of cyclosporins in serum by column-switching highperformance liquid chromatography (HPLC) is described. To increase the analytical recoveries of cyclosporins in serum, serum was diluted to 4 times with a solution containing 10% of 1, 1, 3, 3-tetramethylurea and 0.05 % of sodium dodecylsulfate. A 1000-μl of the mixture was directly injected onto a TSK precolumn PW. After washing the precolumn with water for 10 min, the precolumn-connection was switched to introduce the retained substances onto an analytical column, TSKgel OH-100RP. Cyclosporins were separated with acetonitrile/water (40: 60.v/v) within 30 min. The column temperatures were at room temperature for the precolumn and at 70° for the analytical column. By the present method, the analytical recovery (70%), detection limit (20ng/m1), and within-run reproducibility (5.7% for 250ng/ml, 3.4% for 500ng/ml, 1.2% for 1000ng/ml) were sufficient for therapeutic monitoring of cyclosporin A.
