DETERMINATION OF AMIDE-TYPE LOCAL-ANESTHETICS BY DIRECT-INJECTION OF PLASMA IN A COLUMN-SWITCHING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC SYSTEM USING A PRECOLUMN WITH A SEMIPERMEABLE SURFACE

A high-performance liquid chromatographic method using column switchin g was applied to the direct determination of two local anaesthetics, r opivacaine and bupivacaine, in human plasma. The method is intended to be used in a combined LC-GC system; here only the LC-part is describe d. After addition of internal standard, the samples were filtered and directly injected into a semipermeable surface (SPS) pre-column where the analytes were strongly retained and separated from many endogenous compounds by a short washing step. The retained analytes were transfe rred by a buffered methanol phase from the pre-column into a carbonace ous HPLC column and they were detected by UV detection at 254 nm. The SPS pre-column could withstand numerous (> 200) direct injections of p lasma samples (10 mu l). The method has a detection limit of 8.2 ng an d requires a total assay time of 15 min per plasma sample. Quantitativ e recoveries were obtained over the range 3.3-114 mu g/ml with inter-d ay precisions of 1.6-5.2% (C.V.).