LAUSR

Abstract Levodopa, the metabolic precursor of dopamine, is usually administrated in combination with carbidopa to control dopamine levels in an appropriate manner and reduce side effects in the treatment of Parkinson's disease. In this study, a selective and sensitive high performance liquid chromatography coupled with on-line gold nanoparticles-catalyzed luminol chemiluminescence method for simultaneous determination of levodopa and carbidopa was developed. This method was based on the strongly enhanced chemiluminescence signal of on-line gold nanoparticles-catalyzed luminol-H2O2 system by levodopa and carbidopa. The possible enhancement mechanism was attributed to that levodopa and carbidopa could promote the on-line formation of a large number of gold nanoparticles, which catalyzed the luminol-H2O2 chemiluminescence reaction. The good separation of levodopa and carbidopa was achieved with isocratic elution using a mixture of methanol and 0.2% aqueous phosphoric acid (5:95, V/V) within 10.5 min. Under the optimal conditions, the linear ranges of levodopa and carbidopa were 2.24–448 ng mL−1 and 4.32–1080 ng mL− with the detection limits of 0.89 and 1.08 ng mL− (S/N = 3), corresponding to 17.92 and 21.60 pg for 20 μL sample injection, respectively. The validated method was successfully applied to simultaneous quantification of levodopa and carbidopa in controlled-release tablets (Sinemet®) and human plasma. The average recoveries of levodopa and carbidopa in the tablets were 100.5% and 103.1% with the precisions (RSDs) of 2.4% and 4.0%. The recoveries of levodopa and carbidopa in human plasma ranged from 97.0% to 103.5% with RSDs of no more than 3.3%.