Preparation Of Polymer Brushes Mixed-mode Stationary Phase With Controllable Polarity/Charge And Its Chromatographic Performance

Mixed-mode chromatography(MMC)possesses the merits of high selectivity and is one of the most methods for selective separation of complex samples.The structure of stationary phase is an important factor to influence the MMC separation.In principle,the preparation of MMC stationary phase often adopts to immobilize the different types of functional groups on the surface of substrate by different types of chemical modifications.However,the existing methods are difficult to tune the density and proportion of functional groups on the surface of stationary phase,leading to unadjustable separation selectivity.To solve this problem,this paper selects two or three functional monomers to graft functional copolymer and block polymers at high density onto silica beads by surface initiated-atom transfer radical polymerization(SI-ATRP)to prepare novel mixed-mode stationary phase.The aim is to explore a novel preparation strategy of MMC stationary phase with controllable polarity and charge.The contents are as follows:1.Preparation of block polymer reverse-phase/ion-exchange mixed-mode stationary phase and its chromatographic performance:A new reverse-phase/ion-exchange(RP/IEC)stationary phase was facilely prepared by grafting of block polymer(poly(St-b-NASS))on the surface of silica using hydrophobic styrene(St)and ionic sodium 4-styrenesulfonate(NASS)via two-steps SI-ATRP.The chromatographic properties were investigated by the separation of benzene derivatives,anilines and?-agonists,demonstrating the stationary phase possessed both hydrophobic and ion-exchange interactions of multiple retention mechanisms.Under isocratic elution,the developed stationary phase can be used to simultaneous separation of mixtures with a very wide polar distribution(non-polar,highly polar and charged solutes)and overcome the disadvantages that the RP column must simultaneously separate those solutes under the gradient elution.In comparison with commercial RP columns,the developed column had superior resolution and selectivity in detection of enzymatic solution of pork liver.The obtained results indicated the proposed strategy,based on grafting diblock polymer with two types of monomer on substrate by sequential SI-ATRP,open up a new method for the preparation of mixed-mode stationary phase.2.Preparation of copolymer hydrophilic interaction/ion-exchange mixed-mode stationary phase and its chromatographic performance:The mixture of sodium 4-styrenesulfonate(NASS)and dimethylaminoethyl methacrylate(DMAEMA)underwent SI-ATRP to bond poly(NASS-co-DMAEMA)on the surface of silica to prepare hydrophilic interaction/ion-exchange(HILIC/IEC)mixed-mode stationary phase.Various analytes(neutral,acidic,basic analytes and strong polar nucleosides)were employed to investigate the influences of the ratios of monomers and the composition of mobile phase on the retention behaviors,indicating the separation selectivity were conveniently manipulated by the ratios of NASS to DMAEMA monomer.Additionally,tuning the ratios of DMAEMA in the mixture can adjust the temperature-responsive characteristics of columns owing to temperature-sensitive property of DMAEMA polymer.Moreover,the application of the developed column was demonstrated by the successful separation of nucleosides,?-agonists and safflower injection.In this chapter,it is proved that the construction of copolymer brushes on the surface of silica is an effective approach to prepare the MMC stationary phase with controllable polarity and charge.3.Comparison of chromatographic properties of block polymer and copolymer hydrophilic/ion-exchange mixed-mode stationary phases:Ionic NASS and DMAEMA as functional monomers,the block polymer HILIC/IEC stationary phase was obtained by the two-steps SI-ATRP.The retention mechanism of the block polymer and copolymer HILIC/IEC columns was verified by the partitioning,adsorptive and mixed mechanism,respectively.The results indicated that the two columns conformed to both HILIC and IEC mixed mechanism.Because of the presence of DMAEMA in the polymer chains,the two columns all possessed temperature-sensitive characteristics.Basic?-agonists,nucleosides,and organic acids were employed to investigate the separation selectivity,the block polymer and copolymer columns exhibited the similar hydrophilicity and selectivity in the separation of those analytes.The separation of safflower injection by two columns obtained almost the same analysis results.Since SI-ATRP can well control the polarity and charge on the surface of stationary phase,the stationary phase with the different structure of polymer chains by different polymer methods possess the same property of MMC.4.Preparation of reverse-phase/hydrophilic interaction/ion-exchange mixed-mode stationary phase and its chromatographic performance:Application in the preparation of three modes MMC stationary phase via SI-ATRP,the three monomers:hydrophobic lauryl methacrylate(LMA),hydrophilic hydroxyethyl methacrylate(HEMA)and ionic DMAEMA,were mixture to undergo SI-ATRP to bond poly(LMA-co-HEMA-co-DMAEMA)on silica for the preparation of RP/HILIC/IEC mixed-mode stationary phases.Investigation of the retention behaviors of various analytes on three columns with the different monomer ratios,the results certified that the separation selectivity was manipulated by the ratios of functional monomers.In per aqueous liquid chromatography(PALC),the developed stationary phases can effectively separate organic acids under the very low organic solvent conditions.Application in the analysis of compound vitamin,the separation selectivity can be improved by the tuning the composition of polymer chains on the surface of silica.All results testified that SI-ATRP by grafting polymer brushed with kinds of functional groups is an effective method for the preparation of multi-mode of MMC stationary phases with controllable polarity and charge.