Spectrophotometric methods for the determination of letrozole in bulk and pharmaceutical dosage forms

Ultraviolet (UV), first derivative, second derivative, and AUC-spectrophotometric methods for the determination of letrozole in pharmaceutical formulations have been developed. For UV-spectrophotometry, the standard solutions were measured at 240.0 nm. The linearity ranges were found to be 0.25–20.0 μgml(–1) in methanol and the regression equation was A=1.20×10(–1)C+2.22×10(–2)(r(2)=0.9994). For the first derivative spectrophotometry, the response (dA/dλ) of standard solutions was measured at 224.0 nm. The calibration curve was constructed by plotting dA/dλ values against concentrations 0.25–20.0 μgml(–1), of letrozole. The regression equation of the linear calibration graph was calculated as D(1)=3.89×10(–3)C+1.85×10(–4)(r(2)=0.9987). For the second derivative spectrophotometry, the response (d(2)A/dλ(2)) of standard solutions was measured at 241.0 nm. The calibration curve was constructed by plotting d(2)A/dλ(2) values against concentrations 0.5–20.0 μgml(–1) of letrozole standards in methanol. The regression equation of the linear calibration graph was calculated as D(2)=-1.59×10(–3)C-4.66×10(–4)(r(2)=0.9985). The AUC-spectrophotometric method was based on the calculation of Area under Curve (AUC), for analysis of letrozole in the wavelength range of 235.0–245.0 nm. The calibration curve was constructed by plotting AUC values against concentrations 0.25–20.0 μgml(–1), of letrozole. The regression equation of the linear calibration graph was calculated as AUC=1.132C+0.2153 (r(2)=0.9994). The methods were validated by following the analytical performance parameters suggested by the International Conference on Harmonization (ICH). All validation parameters were within the acceptable range. The developed methods were successfully applied to estimate the amount of letrozole in pharmaceutical formulations.