Development and validation of an HPLC assay for fentanyl and related substances in fentanyl citrate injection, USP

The stability indicating properties of the USP method for the assay of fentanyl in fentanyl citrate injection were evaluated [1] by analyzing fentanyl drug substance and product after acid, hydrogen peroxide, heat, and light treatment. N-phenyl-N-(4-piperidinyl)propionamide (PPA), which is a known degradation product/process impurity of fentanyl, was not adequately resolved from the fentanyl peak, and mobile phase adjustments did not improve the resolution (Fig. 1). Therefore, the USP method did not meet the requirements for a stability-indicating assay. In addition, the wavelength in the USP method was too high (230 nm) to provide adequate levels for the quantitation of the related substances of fentanyl and, in addition, the acetate ions in the mobile phase could interfere with a lower wavelength detection. An isocratic, reversed phase, stability indicating, high performance liquid chromatographic (HPLC) method for the assay of fentanyl and related substances in fentanyl citrate injection, USP has been developed and validated. The chromatographic conditions employed an Inertsil C8, 5 column (25 cm x 4.6 mm), a mobile phase of aqueous perchloric acid [0.23%, w/v]-acetonitrile [65:35, v/v], and ultraviolet (UV) detection at 206 nm. Under the chromatographic conditions of the method, PPA and seven other known process impurities were separated from the active. Degradation studies showed that the active eluted as a spectrally pure peak resolved from its degradation products.