Development and validation of a chiral LC-MS method for the enantiomeric resolution of (+) and (-)-medetomidine in equine plasma by using polysaccharide-based chiral stationary phases.

The detection and separation of medetomidine enantiomers from the complex biological matrices poses a great analytical challenge, especially in the field of forensic toxicology and pharmacology. Couple of researchers reported resolution of medetomidine using protein-based chiral columns, but the reported method is quiet challenging and tedious to be employed for routine analysis. This research paper reported a method that enables the enantio-separation of medetomidine by using polysaccharide cellulose chiral column. The use of chiralcel OJ-3R column was found to have the highest potential for successful chiral resolution. Ammonium hydrogen carbonate was the ideal buffer salt for chiral liquid chromatography (LC) with electrospray ionization (ESI)+ mass spectrometry (MS) detection for the successful separation and detection of racemic compound. The method was linear over the range of 0 to 20 ng/mL in equine plasma and the inter-day precisions of levomedetomidine, dexmedetomidine were 1.36% and 1.89%, respectively. The accuracy of levomedetomidine was in the range of 99.25% to 101.57% and that for dexmedetomidine was 99.17% to 100.99%. The limits of quantification for both isomers were 0.2 ng/mL. Recovery and matrix effect on the analytes were also evaluated. Under the optimized conditions, the validated method can be adapted for the identification and resolution of the medetomidine enantiomers in different matrices used for drug testing and analysis.

An improved liquid chromatography tandem mass spectrometry (LC-MS/MS) method for quantification of dexmedetomidine concentrations in samples of human plasma.

Dexmedetomidine (DMET) is a sedative, analgesic and anxiolytic with minimum adverse respiratory effects. An LC-MS/MS bioanalytical method has been developed and validated to accurately measure DMET concentrations in samples of human plasma. The method overcomes difficulties in the extraction and quantification of DMET due to the fact that it binds strongly to glass and plastic tubes, as well as solid phase extraction (SPE) cartridges. Human plasma (50 µL) was mixed with the internal standard (IS) (DMET-d4) solution (100 µL) and 0.1% formic acid (50 µL) and extracted using Oasis HLB 1 CC (30 mg) solid phase extraction (SPE) cartridges (Waters®). The glass tubes were coated with bovine serum albumin (BSA) 0.5% (20 µL) before eluting DMET and the IS. After evaporation under nitrogen at room temperature, the analytes were reconstituted in 20% acetonitrile in 0.1% formic acid in water and transferred to silanized glass vials. An electrospray ionisation (ESI) mass spectrometry method in positive mode was created and the precursor/product transitions (m/z) were 201.1 → 95.0 (DMET) and 204.9 → 99.0 (IS). The method was robust and fully validated based on the 2012 EMEA guideline for bioanalytical method validation in the concentration range of 0.5-20 ng/mL. Using this assay, we showed that DMET binds strongly to Extracorporeal Membrane Oxygenation (ECMO) circuits, consistent with expectations for small lipophilic compounds.