IMPROVED CLEANUP PROCEDURE FOR THE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ASSAY OF BUPIVACAINE ENANTIOMERS IN HUMAN PLASMA AND ULTRAFILTRATE IN THE NANOGRAM PER MILLILITER RANGE

A clean-up procedure to obtain a minimal detectable concentration of 5-10 ng bupivacaine enantiomer per milliliter human plasma is described. The procedure consists of precipitation of plasma proteins using acetonitrile, followed by solid-phase extraction using a cyano column. The eluate is then made alkaline, and bupivacaine is extracted using n-hexane. After evaporation of n-hexane, the residue is redissolved in the eluent used for HPLC analysis. The HPLC method has been described previously. The minimal detectable concentrations using this method are ca. 8 and 10 ng/ml for R-(+)- and S-(-)-bupivacaine, respectively. For both enantiomers, r(2) is >0.995 over the range of 9.5-760 ng/ml enantiomer.