Spectral resolution techniques for the simultaneous spectrophotometric determination of anti-Parkinson drugs in their combined pharmaceutical dosage form and biological sample based on multivariate calibration and absorbance subtraction methods.

In this study, simultaneous determination of levodopa (LEV) and carbidopa (CBD) in binary mixtures, pharmaceutical formulation, and biological sample was conducted using the application of simple, fast, sensitive, and accurate UV-spectrophotometry in combination with chemometrics methods. The first method is net analyte signal (NAS) based on the multivariate calibration methods. The limit of detection (LOD) and limit of quantification (LOQ) were 0.9758, 0.7633 µg/mL and 2.956, 2.313 µg/mL over the linear range of 5-40 and 0.5-20 µg/mL for LEV and CBD, respectively. In the NAS approach, the mean recovery values of mixtures were 100.12 % for LEV and 99.65 % for CBD, where root mean square error (RMSE) values were 0.0106 and 0.0141 for LEV and CBD, respectively. The second method is absorbance subtraction (AS) based on the absorption factor technique for analyzing the isosbestic point. This model was constructed at an isosbestic point of 261 nm in the range of 5-40 and 0.5-20 µg/mL with coefficient determination (R) of 0.9985 and 0.9996 for LEV and CBD, respectively. AS method could estimate LEV and CBD with LOD values of 1.924 and 0.5657 μg/mL and LOQ values of 5.833 and 1.714 μg/mL, respectively. The recovery percentage was between 91.50 % to 104.60 % with RMSE of 0.1455 for LEV and 92.00 % to 106.66 % with RMSE of 0.2508 for CBD. The introduced approaches have the benefit of concurrent analysis of the mentioned components without any pretreatment. Statistical comparison of the results of real sample analysis with high-performance liquid chromatography (HPLC) did not show a significant difference. These methods can replace HPLC in quality control laboratories when fast, precise, and low-cost analysis is needed.