Construction of a Fluoxetine Ion Chemical Sensor and Its Application for the Determination of pKa Value of Fluoxetine Conjugated Acid, Complexation Study with β-Cyclodextrin and Formulations Assay

A fluoxetine cation sensor of the PVC type, prepared with fluoxetine tetraphenylborate precipitate and 2-nitrophenyloctylether as plasticizer, is described. The sensor exhibits a rapid and slightly sub-Nernstian response (57 mV/pC) to fluoxetine concentrations ranging from 1 × 10−4 to 4.6 × 10−3 M in 0.01 M HCl. No serious interference from common cations (Na+, K+, and ) and pharmaceutical excipients was found, and the sensor was used for the direct assay of fluoxetine in capsules and syrups by means of the calibration graph or the standard addition technique. The results compared favorably with those given by the pharmacopoeia HPLC method. The sensor was also used to determine the pKa of protonated fluoxetine (8.8 ± 0.6) and to study the complexation of fluoxetine with β-cyclodextrin [1:1 stoichiometry, association constant 4.83 (±0.04) × 103 M−1].