Preparation Of Functionalized Porous Materials And Its Application In Tea Caffeine Detection

Caffeine is an important active substance in tea that affects the quality of the tea leaves.Caffeine intake can excite the brain and reduce the risk of cardiovascular disease,but excessive caffeine intake can lead to insomnia and induce anxiety disorders.Currently,the direct analysis of caffeine in tea samples is limited by the complex composition of tea extracts and matrix interference;therefore,there is a need to develop a method with high precision and sensitivity for the adsorption,enrichment and detection of caffeine in tea leaves.In this study,two functionalized porous composites were prepared using covalent organic frameworks（COFs）and metal-organic frameworks（MOFs）as the main targets.The structure and properties of the materials were optimized using various physicochemical characterization methods,and they were used as solid adsorbents in the sample pretreatment.Combined with high performance liquid chromatography tandem mass spectrometry（HPLC-MS/MS）,a rapid and sensitive method for the determination of caffeine in tea was successfully established,which provides technical support for the detection of caffeine in tea.The main results of the study are as follows:1.A layer of metal polyphenol network structure（MPN）was homogeneously synthesized on the surface of COFs using an in situ synthesis strategy,and a porous composite MPN@COFs with high specific surface area（115.7176 m²/g）was successfully prepared,which exhibited a series of experimental conditions（adsorbent dosage,reaction time,ion concentration,p H,etc.）affecting the extraction performance by optimizing the good adsorption performance of caffeine.2.The zeolitic imidazolate framework（ZIF）is a typical class of MOFs materials.A magnetic composite porous material:Fe₃O₄@3DGA@ZIF-8 was successfully prepared by combining magnetic nanoparticles and three-dimensional graphene（3DGA）with ZIF-8 as the raw material using layer-by-layer self-assembly technique.The material was analyzed by various characterization means,and the results showed that the specific surface area of Fe₃O₄@3DGA@ZIF-8 was 162.9754 m²/g,with good reusability,and could be used as a magnetic solid adsorbent for the separation and enrichment of caffeine.3.An HPLC-MS/MS method with good stability and precision for the determination of caffeine was developed.The detection limit（S/N=3）was 0.38μg/L with good linearity in the concentration range of 0.01～1.2 mg/L,which is a rapid and reliable analytical method.4.Caffeine was determined in several different tea samples using the established HPLC-MS/MS method,and the results showed that the recoveries of both functionalized porous composites for caffeine were above 70%,which confirmed the high applicability of the developed method.