Qualitative and quantitative analysis of fluoxetine hydrochloride by ¹⁹F NMR

The chemical shift of fluoxetine hydrochloride appears at δ 14.15 in ¹⁹F NMR analysis.  The δ moved upfield slightly from 14.158 to 14.145 when the concentration of solution became diluted from 2.00 to 0.05 mmol·L⁻¹.  Spiking test was suggested to confirm the existence of the compound for qualitative analysis.  ¹⁹F NMR detection sensitivity test illustrated that a concentration of 17 mg in 1 L water could be detected while the sample was scanned 500 times with optimum parameters.  In quantitative analysis, standard curve of concentration versus fluorine signal intensity was proposed to determine the amount of fluoxetine.  Long capillary tube containing trifluoroacetic acid was used as internal standard for the integration measurements and straight line was obtained with good fitting.  Direct additions of trifluoroethanol to fluoxetine solutions gave a poorer standard curve.