1. A validated enantioselective assay for the simultaneous quantitation of (R)-, (S)-fluoxetine and (R)-, (S)-norfluoxetine in ovine plasma using liquid chromatography with tandem mass spectrometry (LC/MS/MS)
Timothy W Chow, András Szeitz, Dan W Rurak, K Wayne Riggs J Chromatogr B Analyt Technol Biomed Life Sci. 2011 Feb 15;879(5-6):349-58. doi: 10.1016/j.jchromb.2010.12.020. Epub 2010 Dec 29.
A liquid chromatography-tandem mass spectrometry (LC/MS/MS) method was developed and validated for the quantitation of (R)-, (S)-fluoxetine, and (R)-, (S)-norfluoxetine in ovine plasma. The analytes were extracted from ovine plasma at a basic pH using a single-step liquid-liquid extraction with methyl-tert-butyl ether. Chromatographic separation of all enantiomers was achieved using an AGP-chiral column with a run time of 10 min. (R)-, (S)-fluoxetine, and (R)-, (S)-norfluoxetine were quantitated at the total ion current (TIC) of multiple reaction monitoring (MRM) transitions of m/z 310.2→44.1, m/z 310.2→147.7 for (R)-, (S)-fluoxetine, and m/z 296.2→30.3, m/z 296.2→133.9 for (R)-, (S)-norfluoxetine. This method was validated for accuracy, precision, linearity, range, limit of quantitation (LOQ), selectivity, recovery, dilution integrity, matrix effect, and evaluation of carry-over. Observed accuracy ranges were as follows: (R)-fluoxetine -8.82 to 3.75%; (S)-fluoxetine -10.8 to 1.46%; (R)-norfluoxetine -7.50 to 0.37% and (S)-norfluoxetine -8.77% to -1.33%. Observed precision ranges were as follows: (R)-fluoxetine 5.29-11.5%; (S)-fluoxetine 3.91-11.1%; (R)-norfluoxetine 4.32-7.67% and (S)-norfluoxetine -8.77% to -1.33%. The calibration curves were weighted (1/X(2), n=4) and observed to be linear for all analytes with the following r(2) values: (R)-fluoxetine ≥ 0.997; (S)-fluoxetine ≥ 0.996; (R)-norfluoxetine ≥ 0.989 and (S)-norfluoxetine ≥ 0.994. The analytical range of the method was 1-500 ng/ml with an LOQ of 1 ng/ml for all analytes, using a sample volume of 300 μL.
2. Improved enantioselective assay for the determination of fluoxetine and norfluoxetine enantiomers in human plasma by liquid chromatography
Giuliana Gatti, Ilaria Bonomi, Roberto Marchiselli, Cinzia Fattore, Edoardo Spina, Gabriella Scordo, Roberta Pacifici, Emilio Perucca J Chromatogr B Analyt Technol Biomed Life Sci. 2003 Feb 5;784(2):375-83. doi: 10.1016/s1570-0232(02)00820-6.
A simple and innovative assay is described which allows the chiral separation of the four enantiomers of fluoxetine and norfluoxetine, with performance characteristics adequate for therapeutic drug monitoring. The assay requires liquid-liquid extraction into acetonitrile/n-hexane/isopropylic alcohol and re-extraction into phosphoric acid for clean-up. The acidic layer is injected onto the HPLC system after filtering. Separation of the analytes is achieved with a Chiralcel ODR column and a mobile phase consisting of potassium hexafluorophosphate/acetonitrile. Detection is made by ultraviolet absorbance at 227 nm. Standard curves are linear for each enantiomer (r(2)>/=0.992) over the range of 10-1000 ng/ml with a limit of quantification of 10 ng/ml for each enantiomer. Within-day and between-day CV% are
3. Direct stereoselective assay of fluoxetine and norfluoxetine enantiomers in human plasma or serum by two-dimensional gas-liquid chromatography with nitrogen-phosphorus selective detection
Sven Ulrich J Chromatogr B Analyt Technol Biomed Life Sci. 2003 Jan 15;783(2):481-90. doi: 10.1016/s1570-0232(02)00725-0.
A method was developed and validated for the direct enantioselective assay of fluoxetine and norfluoxetine in human plasma or serum by two-dimensional capillary gas-liquid chromatography (GC). A Rtx-1 fused-silica capillary (15 mx0.25 mm I.D., 1.0 micrometer film thickness) and a hydrodex-beta-6-TBDM fused-silica capillary (25 mx0.25 mm I.D., 0.25 micrometer film thickness) were used. A three-step liquid-liquid extraction was used for sample preparation with fluvoxamine and nisoxetine as internal standards. The method provided linear calibration between about 5 and 250 ng/ml for (R)- and (S)-fluoxetine as well as 15 and 250 ng/ml for (R)- and (S)-norfluoxetine. The limits of detection were about 1.5 and 6 ng/ml, respectively. Intra-day precision (coefficient of variation) was estimated as being between 5.4 and 12.7% at plasma levels of 25, 100 and 200 ng/ml for the four enantiomers. Inter-day precision was between 5.3 and 9.1% at 100 ng/ml. The enantioselective separation of some racemic psychopharmaceuticals was tested with various cyclodextrin GC-capillaries. Advantages and disadvantages of direct enantioselective GC are discussed for the assay of racemic psychopharmaceuticals. Samples from a patient who was treated with racemic fluoxetine were measured. In agreement with literature, plasma levels of the (R)-enantiomers of fluoxetine and norfluoxetine were considerably decreased in comparison to the (S)-enantiomers.
