Determination of fluoxetine and its major active metabolite norfluoxetine in human plasma by liquid chromatography-tandem mass spectrometry

A sensitive and specific bioanalytical method for the determination of fluoxetine and norfluoxetine in human plasma has been developed. Automated solid phase extraction on Oasis HLB cartridges was used to extract the analytes from human plasma. Analysis was by reverse phase liquid chromatography on a Xterra MS C18 column using a fast gradient. Fluoxetine, norfluoxetine and fluvoxamine (internal standard) were ionised using the Turbolonspray interface operating in positive ion mode. Detection was via multiple reaction monitoring (MRM) of the characteristic ion dissociation transitions m/z 310.3-->44.1, 296.2-->134.3 and 319.2-->71.1 for fluoxetine, norfluoxetine and fluvoxamine respectively The method is linear over the range 0.5-50 ng mL(-1) (using a sample volume of 0.5 mL). The method is accurate and precise with intra-batch and inter-batch precision (%CV) of < 15% and accuracy (%RE) of < +/-15% for both analytes. A run time of 4 minutes means a high throughput of samples can be achieved. The method has been be used to support a clinical study.