The absorbance of the final solution was scanned in the range of 200�C400 nm, against methanol as the blank. Atovaquone showed absorbance maxima at 251 nm [Figure 2]. The drug followed linearity in the concentration range of 1�C10 ��g/mL (Y = 0.111 x + 0.012, R2 = 0.9990) [Figure 3]. Figure 2 UV-spectrum of atovaquone Figure 3 Calibration curve of atovaquone at 251 nm Preparation of calibration curve for Atovaquone Stock solutions of atovaquone (1�C10 ml) were pipetted out in to a series of 10 volumetric flask of 10 ml. The volume in each volumetric flask was made up to the mark with methanol and the mixer was shacked. That produced the concentration range of 1�C10 ��g/ml of Atovaquone. The absorbances of solutions were measured at 251 nm against methanol as blank [Figure 2]. RESULTS AND DISCUSSION Linearity Under the experimental conditions described, the graph obtained for UV spectroscopy showed linear relationship. Regression analysis using the method of least-squares was made for the slope, intercept and correlation coefficient values. The regression equations of calibration curves was Y = 0.111 x + 0.012 (R2 = 0.9990) for the UV spectroscopy. The range was found to be 1�C10 ��g/ml for UV spectrophotometric methods. The statistical parameters given are the regression equation calculated from the calibration graphs, along with the standard deviations of the slope (Sb) and intercept (Sa) on the ordinate. The results are presented in Table 1. Table 1 Optical characteristics, regression equation and coefficient of the method Recovery studies and validation of the method according to International conference on Harmonization Guidelines[11�C14] To study the accuracy of the above proposed method, recovery studies were carried out by the addition of the standard drug solution to the placebo, and recovery of the drug was calculated. The result of the recovery studies are summarized in Table 2. The precision of the method was studied by carrying out interday and intraday analysis and was expressed as a relative standard deviation. Specificity was checked by spiking the references standard by placebo. The results were found to be satisfactory and are reported in Table 2. Table 2 Recovery method from placebo solution Estimation of Atovaquone in tablet dosage form For analysis of commercial formulation 20 tablets were weighed accurately and triturated to a fine powder. Powder equivalent to 10 mg of Atovaquone was weighed and transferred to a 100 mL volumetric flask. To this, 25 mL of methanol was added and shaken manually for 15 minutes. The volume was made up to the mark with the same solvent and filtered through Whatmann filter paper No. 42. Ten milliliters of this solution was transferred to a 100 mL volumetric flask for further dilution and contained 10 ��g/mL of the solution. An appropriate aliquot was transferred to a 10 mL volumetric flask. The volume was adjusted to the mark and absorbance was recorded at 251 nm.