Electromembrane extraction of anesthetic ketamine on-line coupled to capillary electrophoresis

Abstract

The anesthetic ketamine is extracted from the sample solutions by electromembrane extraction on-line coupled with capillary electrophoresis (CE) at a short separation path. Ketamine is extracted from model acidic and alkaline aqueous solutions, or from untreated human urine as donor into an acidic acceptor solution, which acts also as background electrolyte for CE. Extraction occurs in a flow-through extraction mini probe with an internal volume of 1.1 µL, consisting of a porous hollow fiber with pores filled with nitrophenyloctyl ether as extraction liquid. The probe is immersed in a 1.5 mL vial of analyte solution, the vial is vibrationally agitated during extraction, and ketamine is extracted at 150 V for 300 s. It was found that the pH of the sample solution does not affect the extraction efficiency, i.e., it does not depend on whether ketamine is in the protonated form or as a neutral molecule during extraction; the enrichment factor is 16–19, the recovery factor 1.5 %. The calibration dependence is linear in both model samples in the concentration range 2 to 50 µM and in urine in the concentration range 2.5 to 10 µM with the same slope in both sample types. The LOD values are around 1 µM. The extraction probe is reusable. However, between runs a purification process with the probe immersed in the background electrolyte is necessary to remove ketamine trapped in the membrane liquid.