Iron Oxide Nanoparticles for Absorptive Concentration of Dopamine and Levodopa in Human Plasma and Determined in On-Line Stacking Capillary Electrophoresis

In this study, iron oxide nanoparticles (IONPs) were used for absorptive concentration of dopamine (DA) and levodopa (LD) in plasma, based on the surface-iron (Ⅲ) cations of IONPs and catechol functional group of catecholamine. The extractant was quantified by cation selective exhaustive injection-sweeping micelle electrokinetic chromatography (CSEI-sweeping MEKC). LD was an important drug used in the therapy of Parkinson's disease. However, the peripheral enzyme in human body can easily metabolize LD to DA, leading to a lower drug concentration in human plasma. Therefore, dosage adjustment and therapeutic drug monitoring in patients are needed. After synthesizing, IONPs were equilibrated with analytes for 20 min. Then, 50 uL phosphoric acid (0.1 M) was added for desorption. Finally, the extractant was diluted 10-fold by dd-water. The optimal conditions of CE analysis were as shown below: phosphate rinse buffer (50 mM, pH 2.5) containing 25% methanol, phosphate separation buffer (50 mM，pH 2.5) containing 25% methanol and 100 mM sodium dodecyl sulfate and high conductivity phosphate buffer (pH 2.5, 150 mM). Diluted extractant was injected at 10 kV electrokinetically. The separation was performed at -20 kV and detected at 200 nm. The LOD of DA and LD were 15 ng/mL and 50 ng/mL, respectively. After method validation, calibration curves were established (r ≥ 0.9967), showing good linear relationships. Two real human plasma samples obtained from patients who suffered from Parkinson’s disease were analyzed. DA and LD could be detected in both samples.