Analysis of Counterfeit Sildenafil by Validated UV Spectrophotometric Methods

Abstract

First derivative and ratio derivative UV spectrophotometric methods were developed and validated for determination of sildenafil in some adulterated preparations. Sildenafil is commonly adulterated with paracetamol, metronidazole, and glyburide. This work was mainly oriented toward the analysis of some sildenafil preparations that may be adulterated. First derivative spectrophotometry was applied for determination of sildenafil adulterated with paracetamol at λ= 311.8 nm and 265.8 nm for sildenafil and paracetamol, respectively. The linearity ranges were 10-45 µg/mL and 4-12.5 µg/mL for sildenafil and paracetamol, respectively. First derivative spectrophotometry was also applied for the determination of sildenafil adulterated with metronidazole at λ= 319.5 nm and 291.8 nm for sildenafil and metronidazole, respectively. The linearity ranges were 10-42 and 4-16 µg/mL for sildenafil and metronidazole, respectively. For determination of sildenafil adulterated with glyburide, sildenafil was determined by direct spectrophotometry at λ= 328 nm within linearity range 20-100 µg/mL while glyburide was determined by first derivative of ratio spectra at λ= 316.3 nm using 20 µg/mL of sildenafil as divisor with a linearity range of 30-130 µg/mL by adjusting scaling factor at 10 and Δλ= 4 nm. The developed methods were validated as per International Council for Harmonisation (ICH) guidelines.