Preparation of micropipette tip-based molecularly imprinted monolith for selective micro-solid phase extraction of berberine in plasma and urine samples

A novel berberine-imprinted polymer (MIP) monolith was prepared for extraction of berberine in aqueous medium. The MIP monolith was prepared inside a polypropylene micropipette tip by using dimethylsulfoxide as porogen, acrylamide (AA) as functional monomer and ethyleneglyol dimethacrylate (EGDMA) as cross-linker. Polymerization conditions were optimized and good permeability and selectivity was obtained when the ratio of berberine/AA/EGDMA was 1:5:30. Cross-reaction was also studied by three compounds (palmatine, coptisine, and jatrorrhizine) with similar structure. A molecularly imprinted micro solid-phase extraction (MI-μ-SPE) method was developed for selective extraction of berberine in aqueous solutions. Extraction parameters were investigated, such as sample pH value, sample flow rate, sample volume and elution solvent. By combining with HPLC/UV, MI-μ-SPE method showed a good linear range of 3-800 ng/mL with a low limit of detection limit of 1.0 ng/mL. The method was also applied for the pretreatment of berberine in human plasma and urine samples. The result showed that proteins and other biological matrix were successfully eliminated and berberine was selectively enriched. Recoveries were tested in plasma and urine samples, and calculated to be 90.6-103.2% with relative standard deviations less than 4.7%.