On-line simultaneous deproteinization of biological samples and trace enrichment of three dipine series using a poly(N-isopropylacrylamide-co-ethyleneglycol dimethacrylate) monolith

A porous poly(N-isopropylacrylamide-co-ethyleneglycol dimethacrylate) [poly(NIPAAm-co-EDMA)] monolithic column was prepared by in situ free-radical polymerization. The morphology of monolithic column and pressure drop across the columns were characterized. The results showed excellent permeability and high selectivity. Nifedipine, nitrendipine and nisoldipine were simultaneously selected to validate the extraction efficiency of the prepared monolith both in plasma and urine. The extracted nifedipine, nitrendipine and nisoldipine from plasma and urine samples have been on-line tested quantitatively by using the prepared monolith connected with RP-C18 column. The total analytical run time was 38 min. For all analytes, linear calibration curves were obtained over a range of 2–500 ng/mL with coefficient of correlation > 0.997. Precision for inter- and intra-day assay showed acceptable results for quantitative assay with relative standard deviation (RSD) less than 12%. The accuracy and recovery was found to be in the range of 89–109% and 88–106%. The results indicated that the prepared monolith was feasible to be used as an on-line SPE sorbent material and the method was especially appropriate for multi-analytes monitoring in plasma and urine samples. Finally, the proposed method was successfully applied to simultaneously screen nifedipine, nitrendipine and nisoldipine in plasma.