Automated determination of drugs in serum by liquid chromatography with column-switching. I. Separation of antiepileptic drugs and metabolites.

This is a fully automated system for determining six common antiepileptic drugs and two principal metabolites of carbamazepine in serum. It is based on "high-performance" liquid chromatography (HPLC), with column switching. TSKprecolumn BSA-ODS and TSKgel ODS-120A (both from Toyo Soda) were used as the precolumn and analytical column, respectively. The former contains octadecylsilyl resins treated with bovine serum albumin (BSA), and does not adsorb macromolecules such as serum proteins but retains small lipophilic molecules such as antiepileptic drugs. Serum samples are directly injected onto the precolumn. After washing out the serum proteins from the precolumn with sodium phosphate buffer, we switch the column connections to introduce the retained substances onto the analytical column and elute with a step-gradient of acetonitrile/sodium phosphate buffer. The high analytical recovery (95-102%) and the reproducibilities (CV less than 5% within-run) indicate that this system is suitable for use in theraputic drug monitoring in clinical laboratories.