Determination of six anti-Parkinson drugs using cyclodextrin-capillary electrophoresis method: Application to pharmaceutical dosage forms

A novel capillary electrophoretic method was developed for the assay of two quaternary anti-Parkinson mixtures, entacapone, levodopa, carbidopa, and benserazide (mixture I), and selegiline, levodopa, carbidopa, and benserazide (mixture II), by using α-methyldopa as an internal standard. Furthermore, the method was extended for the determination of another anti-Parkinson drug, lisuride, as well as a psychoactive antihypertensive drug, α-methyldopa, without any modification of the general method. Separation and analyses of all compounds were simply achieved in an untreated fused-silica capillary tube (42.0 cm effective length and 50 μm internal diameter) within 7 minutes under an applied voltage of 20 kV. Optimum separation and analyses were obtained using 25 mM borate buffer (pH 9.5) containing 5 mM β-cyclodextrin as the background electrolyte. The apparatus was equipped with a diode array detector (DAD) to identify lisuride at 240 nm and all other drugs at 200 nm. The addition of 5 mM β-cyclodextrin to the borate buffer has a significant effect on the separation of entacapone and benserazide in mixture I, and on the separation of selegiline and benserazide in mixture II, which cannot be achieved without it. The proposed method was successfully applied to analyse the studied drugs in their multi-component and single-component pharmaceutical dosage forms. The analytical results proved the linearity (r² ≥ 0.9997), accuracy, precision (% RSD < 2), and selectivity of the proposed capillary electrophoretic method.