Development of magnetic solid phase extraction based on magnetic chitosan-graphene oxide nanoparticles and deep eutectic solvents for the determination of flavonoids by high performance liquid chromatography

Determination of bioactive flavonoids using β-cyclodextrin combined with chitosan-modified magnetic nanoparticles

To accurately determine flavonoids (rutin, quercetin or kaempferol), it is necessary to extract them from complex matrices. The ultrasound-assisted magnetic dispersion microsolid phase extraction technique has been predominantly used for separation and enrichment of the target analytes. The combination of magnetic chitosan nanoparticles and a deep eutectic supramolecular solvent (DESP) is likely to enhance the efficiency of flavonoid extraction from food. In this study, adsorbents were prepared by modifying chitosan with magnetic nanoparticles, and the eluent was a DESP derived from β-cyclodextrin and an organic acid. The successful preparation of these materials was confirmed by FTIR, XRD, FE-SEM and 1H NMR. The extraction recovery rates exceeded 93 %, with limits of detection and quantitation ranging from 0.9 to 2.4 μg/L and 2.7 to 7.2 μg/L, respectively, and the flavonoid clearance rates for ABTS and DPPH radicals reached 100 %. Therefore, the integration of magnetic chitosan nanoparticles with the DESP provides a new and efficient method for the extraction of flavonoids while also presenting a potential application of the DESP in separations.

A stable core-shell metal-organic framework@covalent organic framework composite as solid-phase extraction adsorbent for selective enrichment and determination of flavonoids

Hydrophobization and stability is crucial for the practical application of most metal-organic frameworks (MOFs) in extraction technique. In this study, a stable core-shell MOF@COF composite (NH2-MIL-101(Fe)@TAPB-FPBA-COF) was successfully prepared by Schiff base reaction and applied to solid-phase extraction (SPE) of hydrophobic flavonoids. Notably, the TAPB-FPBA-COF shell acts as a hydrophobic "shield", which not only improves the hydrophobicity and stability of hydrophilic NH2-MIL-101(Fe), but also makes the extraction efficiency of flavonoids from MOF@COF composite significantly higher than that of pure NH2-MIL-101(Fe) and TAPB-FPBA-COF. In addition, a sensitive analytical method with excellent linearities (0.1-500 ng mL-1, R2 ≥ 0.9967), low limits of detection (0.02-0.04 ng mL-1 for water; 0.04-0.07 ng mL-1 for grape juice; 0.06-0.08 ng mL-1 for honey), good repeatability (intra-day/inter-day precision are 1.86-5.37%/1.82-7.79%, respectively) and only 5 mg of adsorbent per cartridge was established by optimizing the SPE process combined with high performance liquid chromatography with ultraviolet-visible detector (HPLC-UV). Meanwhile, selectivity study and comparative experiments with the commercial C18 adsorbent showed that the MOF@COF adsorbent exhibited satisfactory extraction efficiency for flavonoids due to multiple interactions such as hydrogen bonding, hydrophobic, and π-π interactions. Finally, the good recoveries in grape juice (84.5-102.5%) and honey (87.5-104.6%) samples further validated the applicability of the proposed method in complex samples.