Preparation And Properties Study Of Temperature-Sensitive Molecularly Imprinted Hydrogel

In recent years,temperature-sensitive molecularly imprinted hydrogels have attracted increasing attention,because of their good recognition and superior temperature-sensitive properties.Caffeine and L-theanine are the most abundant alkaloid and amino acid in tea respectively which have been widely used in many fields,as a research focus in the extraction and separation of the effective components in tea.Taking caffeine and L-theanine for template molecules,we prepared two kinds of molecularly imprinted hydrogel microspheres through the suspension polymerization method and then their swelling degree,the ability of temperature-sensive adsorption and release,and recognition properties were studied.Moreover,online dynamic adsorption processes of temperature-sensitive molecularly imprinted hydrogels were carried out using the microspheres prepared as solid phase extraction column packing by the optimized conditions.Firstly,caffeine molecularly imprinted hydrogel microspheres were prepared by suspension polymerization under the condition of 60 ℃ heat polymerization,using caffeine as template molecule,alpha methylacrylic acid as functional monomer,and poly N-isopropylacrylamide as temperature-sensitive monomer,ethylene glycol dimethacrylate as crosslinking agent.The LCST of the microspheres was 36.3 ℃,showing good temperature-sensitive performance.The adsorption quantity of the microspheres above has reached 6.21 mg/g,1.71 times of non-imprinted gel.At 50 ℃,the adsorption equilibrium time of TMIP was shortened by 30%,while at 20 ℃ the releasing equilibrium time can be reduced by 50%.The elution effect of TMIP was good,and the elution rate was 85.1%.Compared to analogue theophylline,TMIP of caffeine showed the highest selectivity and the selectivity coefficient was 1.78.Secondly,through suspension polymerization,L-theanine temperature-sensitive molecularly imprinted hydrogels were obtained using L-theanine as template molecule.The LCST of the gels was 31.3 ℃,and the adsorption quantity was 5.37 mg/g,1.67 times of non-imprinted gel.The TMIP Scatchard curve indicated that the specific adsorption of TMIP was stronger.At 50 ℃,the adsorption equilibrium time of TMIP was shortened by 20%,while at 20 ℃ the releasing equilibrium time can be reduced by 25%.The elution rate of TMIP was higher than MIP,up to 77.6%.L-theanine temperature-sensitive molecularly imprinted hydrogel showed the highest selectivity to L-theanine,and the selectivity coefficient was 2.54.Finally,dynamic adsorption processes were performed,using caffeine and L-theanine TMIP microspheres as SPE packing,respectively.Through optimizing the conditions,the recovery of caffeine can reach 83.6%and L-theanine reached 73.9%.Compared with static adsorption process,the dynamic adsorption rate of TMIP has increased by 94%and 93.8%for L-theanine and caffeine,respectively.Increasing the temperature of the samples,the adsorption rate of caffeine and L-theanine molecularly imprinted columns were both obviously improved.Making tea liquid as the actual sample and using HPLC to test the caffeine content of the sample which being through the caffeine TMIP column,the results indicated that the column showed good adsorption to caffeine which in tea liquid samples.