Drug-drug adsorption-based miniaturized solid phase extraction of amlodipine from biological samples before HPLC-PDA analysis

A nifedipine-assisted miniaturized solid phase extraction coupled with high-performance liquid chromatography-photodiode array method was developed for the extraction and quantification of amlodipine in biological samples. The extraction process was optimized by evaluating the influence of key parameters, including nifedipine amount, agitation mode and time, aqueous phase pH, salt addition, and desorption solvent conditions. Optimal performance was obtained using 7 mg of nifedipine, vortex agitation for 3 min, pH 9, without salt addition, and using ethanol (175 µL) as the desorption solvent. Under these conditions, the method showed good analytical sensitivity, with limits of detection and quantification of 0.54 and 1.7 µg L^-1 in deionized water; 2.2 and 6.8 µg L^-1 in plasma; and 1.9 and 6.3 µg L^-1 in urine, respectively. A linear response was observed over the concentration range of 6.8-200 µg L^-1 in plasma, with a correlation coefficient 0.998. The method demonstrated acceptable precision, with relative standard deviation values below 8%, and an extraction recovery of 68 ± 4%. The applicability of the developed method was confirmed through analysis of spiked plasma and urine samples at the concentration levels of 10, 25, and 50 µg L^-1. The relative recovery values ranged between 88% and 96% and indicated negligible matrix effects, which confirms the suitability of the method for reliable determination of amlodipine in biological matrices.