Potentiometric determination of fentanyl in pharmaceutical formulations.

A poly (vinyl chloride) membrane electrode with dibutyl phthalate as plasticizer based on the fentanyl-phosphotungstate ion-association complex as ion-exchange site for the determination of fentanyl citrate in injections was developed. A linear response for 1 x 10(-5)-1 x 10(-2) mol dm(-3) drug with a slope of 55.9 +/- 0.4 mV per decade was established. The optimum pH range was 1-7. The lower detection limit was 5.43 x 10(-6) mol dm(-3) fentanyl citrate (1.827 microg cm(-3), 2.33 x 10(-6) mol dm(-3) fentanyl). There were negligible interference from a number of inorganic cations, structural analogues, and some common drug additives in injections. The electrode proposed had been successfully applied to determine fentanyl citrate in injections. The results correlated well with those obtained by the United States Pharmacopoeia standard procedure.