Preparation of MIL-101(Cr)-NH2/chitosan tip foam and its application in pipette tip solid-phase extraction of puerarin and its metabolites in rat serum

In this study, a tip foam named as MIL-101(Cr)-NH₂/chitosan (MIL-101(Cr)-NH₂/CS) was prepared by cross-linking chitosan (CS) with MIL-101(Cr)-NH₂ using glutaraldehyde as the cross-linking agent. After freeze-drying, the internal structure of the MIL-101(Cr)-NH₂/CS foam became porous, thereby exposing more MIL-101(Cr)-NH₂, enriching binding sites, ensuring efficient adsorption, and allowing smooth passage of the sample solution. This also facilitates the inhalation and extrusion of the sample solution. Based on the unique advantages of the MIL-101(Cr)-NH₂/CS foam, a method combining pipette tip solid-phase extraction (PT-SPE) with high-performance liquid chromatography equipped with a fluorescence detector (HPLC-FLD) was established for the detection of puerarin and its metabolites (e.g., daidzein and equol) in rat serum. The method exhibited good linearity in the range of 0.5 to 5000 ng/mL, with limits of detection (LOD), lower limits of quantification (LLOQ), and limits of quantification (LOQ) ranging from 0.2 to 15 ng/mL, 0.5 to 50 ng/mL, and 1 to 100 ng/mL, respectively. The relative standard deviations (RSDs) of intra-day and inter-day precision for puerarin, daidzein, and equol were less than 19.8 %, meeting relevant regulatory requirements. The extraction recoveries of puerarin, daidzein, and equol ranged from 80.17 % to 91.70 %, 80.02 % to 87.41 %, and 80.29 % to 85.39 %, with corresponding RSDs of 3.2 % to 10.4 %, 11.2 % to 13.8 %, and 7.9 % to 11.1 %. These results indicate that the developed method meets the methodological requirements for the quantitative analysis of biological samples. The application of MIL-101(Cr)-NH₂/CS foam in PT-SPE further expands the application scope of metal-organic frameworks (MOFs) in solid-phase extraction (SPE) and provides a reference for PT-SPE technology in handling small-volume samples in complex matrices.