DETERMINATION OF FREE CONCENTRATION OF ROPIVACAINE AND BUPIVACAINE INBLOOD-PLASMA BY ULTRAFILTRATION AND COUPLED-COLUMN LIQUID-CHROMATOGRAPHY

A coupled-column liquid chromatographic method for determining the fre e concentration of ropivacaine and bupivacaine in blood plasma was dev eloped. Following adjustment of the temperature and pH, the plasma sam ples were ultrafiltrated. Ropivacaine or bupivacaine in the ultrafiltr ate was determined by direct injection into a coupled-column liquid ch romatographic system, consisting of one reversed-phase and one ion-exc hange column. The system was highly selective. Ropivacaine and bupivac aine were detected by UV at 210 nm. The limit of determination was 10 nM and the inter-assay precision at a concentration level of about 100 nM was 6% (R.S.D., n = 30) for ropivacaine and 7% (R.S.D., n = 30) fo r bupivacaine.