Microwave-assisted Graphene Oxide Grafted Double Template Imprinted Polymer For Enrichment And Extraction Of Residual Cd(?) And Cu(?) From Vegetables

Food safety is related to human health and life safety.The supervision departments enlarge gradually the management intensity of food security,food poisoning incidents are increasingly frequent.People eat a lot of vegetables every day,but it is difficult to extract and enrich heavy metal from vegetables.Thus,it is crucial to exploit a good selective,low detection limit and low cost analysis method.With its high selectivity,stable chemical structure and strong adsorption capacity,ion imprinted polymers have been considered as the best choice of solid-phase extraction filler recently.Graphene oxides have many oxygen-containing groups,which can be grafted on the surface of double template ion imprinted polymer,thus increasing the adsorption capacity of the composites.At the same time,microwave-assisted technology is added to the reaction process to shorten the reaction time,making the imprinted polymers more stable and uniform.Magnetic graphene oxide grafted double template ion imprinted polymer(MA/Fe₃O₄@GO@Cd/Cu-?P)was prepared by the combination of inverse emulsion and suspension polymerization under the condition of microwave ingestion.It was used for the enrichment of Cd(?)and Cu(?)residues in celery extract.The morphology,composition and structure of MA/Fe₃O₄@GO@Cd/Cu-?P was characterized by SEM,TEM,FTIR,XRD and TG.The RSM based on Box-Behnken design was used to optimize the four factors,for example,the adsorption time(10-70min),pH value(4-10),temperature(293-313K)and initial concentration(10-70mg/L).Under the interaction of the four factors,the influence degree of adsorption capacity of target ions is pH>concentration>time>temperature.The maximum adsorption amount of Cu(?)and Cd(?)were 128.97 and 69.78mg/g when the initial concentration was 40mg/L,pH=7,the time was 40min and the temperature was 303K.Under different pH values,pseudo-first-order,pseudo-second-order and intra-particle diffusion model were used to analyze and evaluate the whole adsorption process.The adsorption of Cu(?)and Cd(?)by MA/Fe₃O₄@GO@Cd/Cu-?P accorded with pseudo second order model.The adsorption reaction between MA/Fe₃O₄@GO@Cd/Cu-?P and target ions is mainly controlled by the chemical adsorption behavior,which may be affected by a single factor of intra-particle diffusion.The adsorption isotherm showed that the Langmuir isotherm could better describe the adsorption of Cu(?)and Cd(?)in MA/Fe₃O₄@GO@Cd/Cu-?P.The reaction mechanism on MA/Fe₃O₄@GO@Cd/Cu-?P is that the adsorption sites are evenly distributed,and the adsorption process is dominated by monolayer adsorption.MA/Fe₃O₄@GO@Cd/Cu-?P was used as a SPE adsorbent,and the influencing factors of SPE were studied.The influences of the variety,concentration and volume of eluent,the concentration,volume and pH value of celery extract,the flow velocity of loading and eluting,ionic strength,interference ion and repeatability on the SPE efficiency of residual Cu(?)and Cd(?)in celery extract were assessed.The concentration and volume of HCl were 0.5mol/L and 3m L separately,the concentration and volume of extract were 10?g/L and 5m L separately,pH=7,and the flow velocity of loading and eluting was 2m L/min,the SPE efficiency of Cu(?)and Cd(?)reached a extreme value.The efficiency of SPE enlargements with the accretion of ionic strength.In addition,in the mixed matrix environment,the efficiency of SPE is almost not affected by external interference ions.After five adsorption-desorption cycles,the efficiency of SPE did not change significantly,indicating that polymer has stable structure and can be reused.The detection limits of Cu(?)and Cd(?)were 0.88?1.95?g/L and 0.021?0.069?g/L,respectively,and the relative standard deviations were 2.074?3.936%and 1.275?3.448%,respectively.The highest recoveries of Cu(?)and Cd(?)were 93%?100%.It can be widely used for the determination of Cd(?)and Cu(?)in the extracts of celery,potato,pleurotus ostreatus,rape,tomato,lettuce,chives,shiitake.