This mixture was sonicated in bath sonicator for 45 minutes and the volume is made up to 100 ml with methanol. It was then filtered through Whatmann filter paper. Then 5 ml of the filtrate was transferred in a 50 ml volumetric flask and the volume was made up to the mark to give a resultant concentration of 100 ��g/ml. Appropriate volumes of this solution were taken according to the procedures described earlier for methods A and B. Validation of the methods Various concentrations of aceclofenac were tested to fix the linearity range of the methods; 1-200 ��g/ml for method A and 1-100 ��g/ml for method B were selected based on the correlation coefficient values [Table 1]. The limit of detection (LOD) and limit of quantification (LOQ) were calculated according to the current ICH guidelines.[16] LOD and LOQ were calculated as 3.3 and 10 standard deviation of the blank (n = 3), respectively, divided by the slope of the calibration line. The optical characteristics such as correlation co-efficient, slope, intercept, molar absorptivity, sandel’s sensitivity were calculated. [The optical characteristics such as Beer's law limits and molar absorptivity values, together with other analytical performance characteristics such as LOD, LOQ, regression equation parameters are given in [Table 1]. Moreover, two commercial formulations of aceclofenac tablets were successfully analyzed by the proposed methods and the values obtained by the proposed methods are given in Table 2. Table 1 Optical characteristics of aceclofenac Table 2 Assay of commercial formulation The accuracy of methods was evaluated by recovery studies.[16] A known amount of standard drug material was added with pre-analyzed formulation in different levels. The amount of drug recovered was calculated and the percentage recovery was determined [Table 3]. The evaluation of robustness was performed by evaluating the inter-day and intra-day precision of the methods. For this purpose, the analysis of formulation was carried out for three times in the same day and on three successive days [Table 4]. Table 3 Intraday and interday precision of the method Table 4 Recovery studies RESULTS AND DISCUSSION Method development The proposed spectrophotometric methods are indirect and are based on determination of aceclofenac after its reaction with either PDAC or MBTH and measuring the chromogen at the respective ��max. Preliminary experiments were conducted to determine the optimum concentration and volumes of PDAC and MBTH to give the highest response. A volume of 3 ml of PDAC (0.25% w/v) and 1 ml of perchloric acid (1%, w/v) for method A and 2 ml of MBTH (0.25%, w/v) and 1 ml of ferric chloride (0.1%, w/v) for method B were fixed. The optimum time required for the reaction completion in two methods was studied and was discovered that the reaction of aceclofenac with PDAC requires 10 min and aceclofenac that of with MBTH requires 20 min.