High-performance liquid chromatographic determination of ropivacaine, 3-hydroxy-ropivacaine, 4-hydroxy-ropivacaine and 2',6'-pipecoloxylidide in plasma.

A sensitive HPLC method has been developed for the determination of ropivacaine, 3-hydroxy-ropivacaine, 4-hydroxy-ropivacaine and 2',6'-pipecoloxylidide in plasma. The procedure involved extraction from plasma with a mixture of n-heptane-ethyl acetate and a back-extraction into an acidified aqueous solution. The chromatography was achieved using a LiChrospher RPB C8 column with a mobile phase consisting of a mixture of acetonitrile and pH 2.1, 0.01 M potassium dihydrogenphosphate, the latter phase containing 0.005 M 1-heptanesulfonic acid for ropivacaine metabolites analysis. The extraction yields of ropivacaine, 3-hydroxy-ropivacaine, 4-hydroxy-ropivacaine and 2',6'-pipecoloxylidide were 94.7%, 79.4%, 79.4% and 77.7%, respectively. The limits of detection of ropivacaine, 3-hydroxy-ropivacaine, 4-hydroxy-ropivacaine and 2',6'-pipecoloxylidide in plasma samples were 0.9 ng/ml, 3 ng/ml, 5 ng/ml and 1 ng/ml, respectively.