A new reversed-phase/strong anion-exchange mixed-mode stationary phase based on polar-copolymerized approach and its application in the enrichment of aristolochic acids.

A novel silica-based reversed-phase/strong anion-exchange mixed-mode stationary phase named C18SAX was synthesized based on the polar-copolymerized approach. C18SAX stationary phase showed excellent compatibility with 100% aqueous mobile phase and comparable performance with commercial SunFire™ C18 column in terms of column efficiency and methylene selectivity. And the results indicated that hydrophobic interaction and anion-exchange mechanism dominate the separation process of aristolochic acids. The utility of C18SAX material-based SPE was demonstrated for the enrichment of aristolochic acids extracted from Caulis Aristochiae Manshuriensis. The SPE method was developed rapidly and simply by HPLC evaluation. Under the optimized SPE conditions, the average recoveries of aristolochic acid I and aristolochic acid II in crude sample were 72.36% and 105.59%, with RSDs of 5.77% and 1.13%, respectively. The complexity of sample matrices was significantly simplified after the SPE procedure and further preparation and purification of target compounds was performed on a preparative C18TDE column. Four aristolochic acids, including aristolochic acid I (31.8 mg), II (8.9 mg), IIIa (6.1 mg) and IVa (4.3 mg) were purified with HPLC purities all above 93%. The results proved that the aristolochic acids could be efficiently enriched by C18SAX material and easily eluted in acidic conditions, indicating its great potential in the enrichment of acidic compounds from complex matrices.