Preparation Of MOFs-POPMs Composite Materials And Online Solid Phase Extraction Of Trace Components In Traditional Chinese Medicines

Traditional Chinese medicines（TCMs）have played a vital role in the treatment of diseases and health care for thousands of years.With the wide application of TCMs,more and more attention has been paid to the natural ingredients in TCMs.However,it is difficult to obtain some trace biological substances through traditional extraction methods because of the complexity of TCMs components.Therefore,it is very necessary to enrich and purify the trace components in TCMs.Metal organic frameworks（MOFs）are a new kind of porous materials composed of metal units with ligands through coordination bonds,which have the advantages of large specific surface area,open metal sites and good thermal stability.In this paper,MOFs were modified and used as monomers to prepare two MOFs-porous organic polymer monoliths composite materials（MOFs-POPMs composite materials）,which were successfully applied to the online enrichment,purification and quantitative analysis of trace components in TCMs.Firstly,the-NH₂ of the MOF material UiO-66-NH₂ was derivatized to carry C=C terminal on its surface.Then the modified UiO-66-NH₂ was used as a comonomer to prepare UiO-66-NH₂-POPMs composite material with crosslinking agent,porogen and initiator.The composite monolithic material was used as an adsorbent for the online solid phase extraction（SPE）of aristolochic acid-I（AA-I）in TCMs.The influence of various experimental conditions on the preparation of UiO-66-NH₂ and UiO-66-NH₂-POPMs composite material were investigated by scanning electron microscopy,infrared,nitrogen adsorption,mercury intrusion,x-ray powder diffraction and other methods.The recovery rate,limit of detection（LOD）,limit of quantitation（LOQ）,precision and stability were used to evaluate the extraction effect of UiO-66-NH₂-POPMs composite material.The results showed that the specific surface area and permeability of the composite monolithic material increased when modified UiO-66-NH₂ was added.What’s more,the adsorption capacity of AA-I has also increased.The good linear relationship in the range of 0.0440～4.00×10²μg/m L showed that this method was good.Moreover,the correlation coefficient r was 0.9994.LOD and LOQ were 13.08 ng/m L and 44.00 ng/m L,respectively.The RSDs of intra-day and inter-day were both less than 1.0%;The average recovery rates were between 91.1%and 106.5%.In addition,a UiO-66-（OH）₂-POPMs composite material was prepared using modified UiO-66-（OH）₂ as monomer.The composite monolithic material was used as an SPE adsorbent to enrich and purify oleanolic acid（OA）in TCMs.The structure and pore size distribution of UiO-66-（OH）₂ and UiO-66-（OH）₂-POPMs composite material have been characterized by a series of methods.The results showed that the addition of modified UiO-66-（OH）₂ can increase the specific surface area and the permeability of the monolithic material.Some influencing factors on extraction efficiency have been systematically investigated,including composition and optimization of the prepolymerization solution,the composition and p H of the mobile phase for enrichment and elution,flow rate,etc.A good linear relationship in the range of 0.590～2.50×10³μg/m L was obtained under the optimum conditions.In addition,the correlation coefficient r was 0.9996.The LOD and the LOQ were 0.18μg/m L and 0.59μg/m L,respectively.The intra-day RSDs and the inter-day RSDs of retention time and peak area were less than 0.9%and 1.3%,respectively.The average recovery rates of OA were between 87.7%and 104.6%.The results showed that the two MOFs-POPMs composite materials prepared in this paper were reliable and accurate for the online SPE of AA-I and OA.This method can be used for online enrichment,purification and content determination of AA-I and OA in TCMs.