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Abstract. The application of biodiesel in internal combustion engines are increasing at a faster rate, due to the fact that biodiesel posses more oxygen content (Approximately 12 %), which helps in the complete combustion of the fuel. On the other hand the production cost of the biodiesel is high compared to mineral diesel fuel. This may be due to the availability of raw oil and its high initial cost. To minimize the high initial cost of the biodiesel used cooking oil is one of the best solutions. In this paper an attempt was made to analyze the fatty acid compositions and other characteristics of used cooking oil. Optimization techniques like response surface methodology (RSM) was successfully used for better yield estimation with the help of advanced software Design Expert. The optimum values of the variables were: oil to methanol ratio (1:8.37), catalyst concentration (0.74 Wt%), reaction temperature (47.950 °C) and reaction time (54.58 min) at 250 rpm. The predicted response value at these optimum values was 96.15 %. To confirm these optimum values, experimentations were conducted based on the optimum values and achieve the yield of 96 %. This shows that the yield of used cooking oil methyl ester is very near to the optimum value with an error of 0.15 % which may be accepted. This showed that the model correctly explains the influence of the process variables on the production of FAME from used cooking oil (UCOME). And from the gas chromatography results there is equal distribution of saturated and unsaturated fatty acids. 14 % oxygen can be acclaimed in UCOME by elemental analysis. Unsaturated level of fatty acids are observed.

A new sensitive and stability indicating reverse phase high-performance liquid chromatography method has been developed for the quantitative determination of potential impurities of Ledipasvir, active pharmaceutical ingredient. Efficient chromatographic separation was achieved on waters × select column contains C18 stationary phase in gradient mode, quantitation at wavelength of 325 nm and mobile phase A is 50 mM ammonium formate pH 3.5 and mobile phase B is acetonitrile with flow rate 1.2 mL. The method was validated according to International Council for Hormonisation guideline, linearity studies has shown correlation coefficient value greater than 0.999 for Ledipasvir and all known impurities. Limit of detection and Limit of quantification were determined to be 0.01% and 0.03%, respectively, for all the impurities. The consistent recoveries were obtained for all impurities (95-105%). Various stress conditions were applied to study the degradation behavior of the drug substance. LC-MS was used to analyse the degraded samples and possible structural identifications were assigned based upon known reactivity of the drug. The method was found to be specific, selective and robust to the degradation products. Major degradation of the drug substance was found to occur under photolytic stress conditions resulting a novel impurity (impurity F). The formed degradant was identified and characterized by FT-IR, 1HNMR and LC-MS/MS. The stress samples quantified against qualified working standard and the mass balance found above 98%.

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