Hydroxypropyl-β-cyclodextrin-assisted Acetonitrile Field-amplified Stacking in Capillary Electrophoresis Enabling Ultra-Trace Quantification of Amlodipine Enantiomers in Human Plasma.

Amlodipine besylate, a third-generation dihydropyridine calcium channel modulator, is routinely prescribed as a racemic mixture in the clinical management of arterial hypertension and ischemic chest pain. Among its enantiomeric pair, (S)-amlodipine is the pharmacologically active form and is primarily responsible for the antihypertensive effect. Given that both (R)- and (S)-amlodipine circulate at extremely low concentrations following oral administration, a highly sensitive analytical method is required for enantioselective monitoring. In this study, we developed a simple, sensitive, and cost-effective capillary electrophoresis (CE) method for clinical application, which integrates hydroxypropyl-β-cyclodextrin-mediated chiral recognition with acetonitrile-driven field-amplified sample stacking. Chiral resolution of trace amlodipine (AML) present in human plasma samples was performed in an uncoated bare fused silica capillary (effective length 31.2 cm, internal diameter 75 µm), thermostated at 25°C and operated with an imposed potential of 15 kV. The running buffer consisted of borate (6.25 mM) and phosphate (25 mM), adjusted to pH 2.5, containing 30 mg/mL hydroxypropyl-β-cyclodextrin, and ultraviolet monitoring was conducted at 200 nm. This assay was fully validated for the quantitative measurement of each AML enantiomer in plasma. For (R)- and (S)-amlodipine, linear calibration was achieved across the range 0.2475-19.80 ng/mL and met the commonly accepted bioanalytical criteria. Comparative pharmacokinetic evaluation demonstrated no statistically significant differences between the concentration-time profiles obtained with the proposed CE method and those generated by a reference liquid chromatography-tandem mass spectrometry assay, confirming the accuracy and reliability of the developed procedure for routine therapeutic drug monitoring.