Rapid electrophoretic monitoring of the anaesthetic ketamine and its metabolite norketamine in rat blood using a contactless conductivity detector to study the pharmacokinetics.

Abstract

A method of capillary electrophoresis with contactless conductivity detection has been developed for non-enantioselective monitoring the anaesthetic ketamine and its main metabolite norketamine. The separation is performed in a 15μm capillary with an overall length of 31.5cm and length to detector of 18cm; inner surface of the capillary is covered with a commercial coating solution to reduce the electroosmotic flow. In an optimised background electrolyte with composition 2M acetic acid + 1% v/v coating solution under application of a high voltage of 30kV, the migration time is 97.1 s for ketamine and 95.8 sfor norketamine, with an electrophoretic resolution of 1.2. The attained detection limit was 83ng/mL (0.3μmol/L) for ketamine and 75ng/mL (0.3μmol/L) for norketamine; the number of theoretic plates for separation of an equimolar model mixture with a concentration of 2μg/mL was 683500plates/m for ketamine and 695400plates/m for norketamine. Laboratory preparation of rat blood plasma is based on mixing 10 μL of plasma with 30 μL of acidified acetonitrile, followed by centrifugation. A pharmacokinetic study demonstrated an exponential decrease in the plasma concentration of ketamine after intravenous application and much slower kinetics for intraperitoneal application.