Simultaneous Estimation of Levodopa, Carbidopa and Entacapone in Bulk and Pharmaceutical Formulations by RP-HPLC Method

A new, simple, precise, accurate and reproducible RP-HPLC method was developed and validated for the simultaneous estimation of levodopa, carbidopa and entacapone in bulk and pharmaceutical formulations. Separation of levodopa, carbidopa and entacapone was successfully achieved on a phenomenex C18 (250mm x 4.6mm x 5µm). The mobile phase consisted of 0.1M Ammonium acetate buffer: methanol (60:40 v/v) at a flow rate of 1.0 ml/min. The response was found to be linear in the concentration range of 50µg/ml to150 µg/ml for levodopa, 12.5 µg/ml to 37.5 µg/ml for carbidopa and 200 µg/ml to 600 µg/ml for entacapone. The value of the correlation coefficient was found to be 0.999, 1.000 and 0.999 for levodopa, carbidopa and entacapone respectively. The LOD and LOQ for levodopa were found to be 0.926 µg/ml and 3.088 µg/ml, respectively. The LOD and LOQ for carbidopa were found to be 0.1917 µg/ml and 0.6389 µg/ml, respectively and LOD and LOQ for entacapone were found to be 2.068 µg/ml and 6.893µg/ml respectively.  This method was found to be good percentage recovery for levodopa, carbidopa and entacapone were found to be 99.00, 99.00 and 100.00 respectively indicates that the proposed method is sufficiently accurate. The specificity of the method shows good correlation between retention times of standard with the sample so, the method specifically determines the analyte in the sample without interference from excipients that are commonly present in tablet dosage forms. The method was extensively validated according to ICH guidelines for linearity, range, accuracy, precision, specificity and robustness.