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 15 μm capillary with an overall length of 31.5 cm and length to detector of 18 cm; inner surface of the capillary is covered with a commercial coating solution to reduce the electroosmotic flow.
In an optimised background electrolyte with composition 2.0 M acetic acid + 1% v/v coating solution under application of a high voltage of 30 kV, the migration time is 97.1 s for ketamine and 95.8 s for norketamine, with an electrophoretic resolution of 1.2. The attained detection limit was 83 ng/mL (0.3 μmol/L) for ketamine and 75 ng/mL (0.3 μmol/L) for norketamine; the number of theoretic plates for separation of an equimolar model mixture with a concentration of 2.0 μg/mL was 683,500 plates/m for ketamine and 695,400 plates/m for norketamine.
Laboratory preparation of rat blood plasma is based on mixing 10 μL the 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.