Research Article Estimation of Tadalafil Using Derivative Spectrophotometry in Bulk Material and in Pharmaceutical Formulation Zamir G. Khan, Amod S. Patil, and Atul A. Shirkhedkar Department of Pharmaceutical Chemistry, R. C. Patel Institute of Pharmaceutical Education & Research, Karwand Naka, Shirpur, Dhule District, Maharashtra 425 405, India Correspondence should be addressed to Atul A. Shirkhedkar; atulshirkhedkar@redifmail.com Received 17 January 2014; Accepted 2 May 2014; Published 21 May 2014 Academic Editor: Craig J. Eckhardt Copyright © 2014 Zamir G. Khan et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Four simple, rapid, accurate, precise, reliable, and economical UV-spectrophotometric methods have been proposed for the determination of tadalafl in bulk and in pharmaceutical formulation. “Method A” is frst order derivative UV spectrophotometry using amplitude, “method B” is frst order derivative UV spectrophotometry using area under curve technique, “method C” is second order derivative UV spectrophotometry using amplitude, and “method D” is second order derivative UV spectrophotometry using area under curve technique. Te developed methods have shown best results in terms of linearity, accuracy, precision, and LOD and LOQ for bulk drug and marketed formulation as well. In N,N-dimethylformamide, tadalafl showed maximum absorbance at 284 nm. For “method A” amplitude was recorded at 297 nm while for “method B” area under curve was integrated in the wavelength range of 290.60–304.40 nm. For “method C” amplitude was measured at 284 nm while for “method D” area under curve was selected in the wavelength range of 280.80–286.20 nm. For methods A and B, tadalafl obeyed Lambert-Beer’s law in the range of 05–50 g/mL while for “methods C and D”, tadalafl obeyed Lambert-Beer’s law in the range of 20–70 g/mL, and-for “methods A, B, C, and D” the correlation coefcients were found to be > than 0.999. 1. Introduction Tadalafl (TD) is (6R,12aS)-6-(1,3-benzodioxol-5-yl)-2,3,6,7, 12,12a-hexahydro-2-methylpyrazino[1  ,2  :1,6] pyrido[3,4-b] indole-1,4-dione [1]. Te chemical structure of tadalafl is shown in Figure 1. Tadalafl is a selective inhibitor of phosphodiesterase type 5 (PDE5) [2]. It is an impotence agent. It is indicated for the treatment of erectile dysfunction [3]. A detailed literature survey for tadalafl revealed that several analytical methods are reported for the determination of tadalafl by high-performance liquid-chromatography [4–8], high-performance thin-layer chromatography [9], spectrofuorimetry [10], and UV-spectrophotometry [11]. To our knowledge no methods were found in literature for determination of tadalafl in bulk and pharmaceuti- cal formulation using derivative spectroscopic techniques. Terefore, our attempt is to develop frst order and second order derivative spectroscopy using amplitude and also area under curve (AUC) techniques. Te AUC method is applicable where there is no sharp peak or when broad spectra are obtained. It involves the calculation of integrated value of area with respect to the wavelength between the two selected wavelengths  1 and  2 . Selection of wavelength range is on the basis of repeated observations so as to get the linearity between AUC and concentration [12]. Further, methods were validated as per ICH guidelines [13]. 2. Experimental Work 2.1. Material and Methods. Tadalafl working standard was obtained from Glenmark Pharmaceuticals Ltd., Mumbai, Hindawi Publishing Corporation International Journal of Spectroscopy Volume 2014, Article ID 392421, 6 pages http://dx.doi.org/10.1155/2014/392421