Monolithic Column Prepared with UiO-66-2COOH MOF as Monomer for Enrichment and Purification of Ursolic Acid in Plants by Online Solid-Phase Extraction

Novel advanced materials and magnetic solid phase extraction as approaches in sample preparation to enhance the analysis of ochratoxin A in peanuts

Ochratoxin A (OTA) is a mycotoxin that can contaminate a variety of agricultural commodities, including fruit juices and wines. The capability of a magnetic solid-phase extraction (MSPE) method with a magnetic metal-organic framework (MOF) material having a three-layer core-shell structure to improve the detection of OTA in food matrices using high performance liquid chromatography is described. Analysis of the material through X-ray diffraction (XRD) indicated the successful synthesis of the magnetic nanomaterial Fe3O4@SiO2@UiO66-NH2. Scanning electron microscopy (SEM) and Zetasizer lab indicated its nano-sized morphological features. The conditions affecting the magnetic solid-phase extraction procedure, such as material dosage, pH, composition and amount of eluent, desorption solution and desorption time were investigated to obtain the optimal extraction conditions. Under optimized conditions, the recoveries of spiked analytes at three different concentrations ranged from 95.83 to 101.5%, and the relative standard deviations were below 5%. Coupling with HPLC allowed the limit of detection to be 0.3 μg kg-1. This method is simple and specific, and can effectively avoid the influence of coexisting elements and improve the sensitivity of determination through fast MSPE of OTA. It has broad development prospects in OTA detection pre-treatment.

Preparation of a novel MOF-POPM and its application in online purification and enrichment of oleanolic acid in medicinal plants

In present work, a method for enrichment, purification, and content determination of oleanolic acid (OA) in medicinal plants was established based on on-line solid phase extraction (SPE). A metal organic frameworks-porous organic polymer monolith (MOF-POPM) was prepared with functionalized UiO-66-(OH)2 as monomer and was used as SPE column for online enrichment and purification of OA. The ratio of adsorbent, enriching and eluting solvent, mobile phase pH, and flow rate had been systematically investigated. Under the optimum conditions, the linear range of OA was 0.59-2500 μg/mL with r = 0.9996. The limit of detection (LOD) was 0.18 μg/mL and the limit of quantification (LOQ) was 0.59 μg/mL. The intra-day relative standard deviations (RSDs) and inter-day RSDs of retention time and peak area were less than 0.3% and 1.3%, respectively. The average recoveries of OA in medicinal plants samples ranged from 87.7 to 104.6%. The results demonstrated that the online system was reliable and accurate for enrichment, purification, and content determination of OA in medicinal plants.

Preparation of poly(ionic liquid@MOF) composite monolithic column and its application in the online enrichment and purification of tectochrysin in medicinal plants

Herein, a poly(ionic liquid@MOF) composite monolithic column was prepared via in situ radical polymerization using ionic liquid (1-allyl-3-methylimidazolium hexafluorophosphate) and MOF (derivatized UIO66-2COOH) as copolymer monomers. The composite monolithic column was characterized via scanning electron microscopy (SEM), nitrogen adsorption-desorption isotherms and mercury intrusion porosimetry. Subsequently, the composite monolithic column combined with high performance liquid chromatography (HPLC) was used as a solid-phase extraction (SPE) absorbent for online purification and enrichment of tectochrysin in medicinal plants. The results indicated that the addition of the ionic liquid and MOF not only increased the surface area but also increased the adsorption capacity of the monolith for tectochrysin. The method showed good linearity in the concentration range of 0.01-500 μg mL^-1. The calibration equation was y = 2154.6x - 8.3785 and the limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N = 10) were 3.33 ng mL^-1 and 10 ng mL^-1, respectively. The relative standard deviation (RSD) of the intra-day and inter-day precision was less than 2.62%, the RSD of inter-column was less than 3.16%, and the recoveries ranged from 100.58% to 105.00%. Thus, results showed that this method is simple, accurate and convenient for the online enrichment and purification of tectochrysin from medicinal plants.