The system suitability assessment for the analytical HPLC method established
instrument performance parameters such as peak area, % R.S.D., column efficiency (N) and USP tailing factor (Tf) for both the analytes. The sample solution was then filtered and 10 μL of the test solution was injected and chromatogram Enzalutamide was recorded for the same and the amounts of the drugs were calculated. The RP-LC-PDA method was validated in terms of precision, accuracy, specificity, sensitivity, robustness and linearity according to ICH guidelines.22 The precision of repeatability was studied by replicate (n = 3) analysis of tablet solutions. The precision was also studied in terms of intra-day changes in peak area of drug solution on the same day and on three different days over a period of one week. The intra-day and inter-day variation was calculated in terms of percentage relative standard deviation. Values of limit of detection (LOD) and limit of quantification (LOQ) were calculated by using σ (standard deviation
of response) and b (slope of the calibration curve) and by using equations, LOD = (3.3 × σ)/b DAPT and LOQ = (10 × σ)/b. Calculated values were confirmed by repeated injection of samples containing amounts of analyte in the range of LOD and LOQ. To determine the robustness of the method, the final experimental conditions were purposely altered and the results were examined. The flow rate was varied by (±) 0.10 ml/min, the percentage of methanol and water was varied by (±) 5%, column temperature was varied by (±) 2 °C, the column was changed from different lots and wavelength of measurement was changed by (±) 1 nm. One factor at a time was changed to estimate the effect. The solutions containing 31.25 μg/ml of DKP and 5 μg/ml of TCS were injected in the column. A number of replicate analyses (n = 3) were conducted at 3 levels of the factor (−, 0, +). Kromasil C18 (5 micron
250 mm × 4.6), column was the most suitable one since it produced symmetrical peaks with high resolution. The UV detector response of dexketoprofen and thiocolchicoside was studied and the best wavelength was found to be 265 nm showing highest sensitivity. Several modifications too in the mobile phase composition were made in order to study the possibilities of changing the selectivity of the chromatographic system. These modifications included the change of the type and ratio of the organic modifier, flow rate, temperature and stability of dexketoprofen and thiocolchicoside were also studied in methanol and mobile phase. Initially no peaks were observed when acetonitrile and phosphate buffer in different ratios were utilized, at temperature of 30 °C and 0.8 ml/min flow rate on a C8 column. So acetonitrile was replaced by methanol, at that time both drugs again didn’t show peaks.