Pre-column switching techniques for the determination of drugs and metabolites in body fluids in research and routine analysis.

The use of a column switching system for direct injection of samples and of a sample clean-up on reversed phase pre-columns is described. The pre-columns were filled with spherical C-18 silica gel of particle size 30 microns. Two applications are reported on: (1) the direct injection of serum samples for the simultaneous analysis of nine antiepileptic drugs and metabolites and (2) the determination of phenytoin and of carbamazepine in serum ultra-filtrates. The purge liquid for the sample clean-up was diluted phosphoric acid, and the eluent mixture for the chromatographic separation was water/acetonitrile. The analytical column (length 12.5 cm) was filled with C-18 silica gel of particle size 5 micron. A gradient elution was chosen for the first application, while the second application was carried out using isocratic chromatographic conditions.