Abstract: A cation exchange monolithic column was prepared with methylacrylic acid (MAA) as the functional monomer and ethylene dimethacrylate (EDMA) as the cross linker. This column was applied to remove the matrix compounds and enrich the ionic medicines in human plasma with water as the mobile phase. As a result, the human plasma samples can be directly injected into chromatographic system. The relationship between the mobile phase flow rate and back pressure was studied. The results showed that the monolithic column had good performances in lower pressure and higher permeability. In addition, the maximum adsorption of nifedipine on this monolithic column was investigated. The on-line clean-up and enrichment of samples were carried out using this column as the solid-phase extraction material and the C18 column as the analytical column. The chromatography was performed on a C18 reversed-phase high performance liquid chromatographic column with ultraviolet detection at 235 nm. The mobile phase was a mixture of methanol-water (70∶30, v/v), and the flow rate was 1.0 mL/min. The linear range of nifedipine in human plasma was 5.0-75.0 μg/L. The intra- and inter-day relative standard deviations (RSDs) were both less than 5.0%. The limit of detection (LOD) was 1 μg/L and the limit of quantification (LOQ) was 4 μg/L. In this method tedious pretreatment procedure is not necessary. It is a fast, economical, reproducible and efficient method for assaying trace nifedipine in human plasma.

Key words: human plasma , nifedipine, on-line analysis, ion exchange monolithic column