Published: Journal of Analytical Toxicology, Volume 21, Number 6, October 1997, pp. 415–419.

Simultaneous Identification and Quantitation of Fluoxetine and its Metabolite, Norfluoxetine, in Biological Samples by GC–MS
Joseph A. Crisfasi, Nha X. Le, and Christopher Long

A sensitive method for the quantitation of fluoxetine and norfluoxetine in biological samples was developed. Blood, urine, and tissue samples were alkalinized and extracted with N-butyl chloride. The extracts were derivatized with pentafluoropropionic anhydride before gas chromatography–mass spectrometry (GC–MS). Selected ions were monitored at m/z 117 and 294 for fluoxetine; m/z 117, 176, and 280 for norfluoxetine; and m/z 122 and 299 for the internal standard fluoxetine-d₅. The within-run and between-run precision as well as recovery were determined for both analytes. The empirical limit of detection was determined to be 12.5 µg/L for both fluoxetine and norfluoxetine, whereas the empirical limit of quantitation was 25 µg/L for both drugs. Calibration curves were linear in the range of 50–1000 µg/L for both analytes. Some drugs that were known or suspected of interfering with high-performance liquid chromatography and GC methods for fluoxetine and norfluoxetine were tested for interference. This is the only reported method that combines the use of a deuterated internal standard, selected ion monitoring by GC–MS, and derivatization for the identification and quantitation of fluoxetine and norfluoxetine.

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