Preparation Of Carbon Nanomaterial Composite Monolith For Online Enrichment And Purification Of Ursolic Acid

Ursolic acid is a naturally occurring pentacyclic triterpenoid carboxyl acid,which exists in many herbs in the form of a free acid.Ursolic acid possesses a wide range of biological activities including liver protection,anti-hepatitis,anti-tumor,anti-bacterial,anti-oxidation and anti-oxidation activities et al.Ursolic acid is widely distributed in plants,but the components contained in plants are complicated,which make it difficult to extract and separate.In addition,the extract of ursolic acid is generally crude and needs further separation and purification.Online solid-phase extraction is a sample pretreatment technique.The conventional adsorbents include C8 and C18 bonded silica adsorbents,but C8 and C18 bonded silica adsorbents not only have a high column pressure,but also have high cost duo to they have low reusability and are easily clogged at the enrichment process.So it is necessary to prepare novel adsorbents for solid-phase extraction.Monolithic column is a separation media comprised of continuous and integrated interconnecting porous skeleton.It has the advantages of low back pressure and high mass transfer efficiency.Though the polymer monolithic columns have been applied to sample pretreatment in various fields,they usually have low adsorption capacity due to their low surface area.To solve this problem,nanoparticles can be incorporated into polymer monolithic column to increase their specific surface area.In this paper,two nanocomposite monolithic columns were prepared using nanomaterials as monomer,and the monolithic columns were used as an adsorbent for on-line enrichment,purification and quantitative analysis of ursolic acid in medicinal plants.Firstly,functionalized graphene oxide(f-GO)was obtained by modifying graphene oxide.Poly(f-GO-co-NIPAAm-co-TMPTA-co-EDMA)nanocomposite monolithic column was prepared by using f-GO and N-isopropylacrylamide(NIPAAm)as comonomers,trimethylpropane triacrylate(TMPTA)and methacrylate(EDMA)as crosslinkers and ammonium persulfate/N,N,N,N-tetramethylethylenediamine(APS/TEMED)as initiator system.The structures of the monolithic columns were characterized by scanning electron microscopy,nitrogen adsorption-desorption method and mercury intursion method.Themonolithic column was combined with high performance liquid chromatography for enrichment and quantitative analysis of ursolic acid in medicinal plants.Compared with the monolithic column only using NIPAAm as the monomer,the composite nano-integrated material had a larger adsorption amount of ursolic acid.The method had good repeatability and high recovery.Secondly,functionalized multi-walled carbon nanotubes(f-MWCNTs)were obtained by modifying hydroxylated multi-walled carbon nanotubes(MWCNTs-OH).Poly(f-MWCNTs-co-ST-co-EDMA)composite monolithic column was prepared by using f-MWCNTs and styrene(ST)as co-monomers,EDMA as crosslinker,benzoyl peroxide/N,N-dimethylaniline(BPO/DMA)as the initiation system.The monolithic column was combined with high performance liquid chromatography for enrichment,purification and quantitative analysis of ursolic acid in the medicinal plants.The results showed that the polymerized nanocomposite monolithic column can be used as adsorbent for online solid-phase enrichment and purification of ursolic acid in various medicinal plants.