Application Of Magnetite/reduced Graphene Oxide Nanocomposites In The Analysis Of Pesticide And Veterinary Drug Residues

Magnetite/reduced graphene oxide(MRGO)nanocomposite is a novel magnetic nanomaterial.It integrates the advantages of grapheme and Fe3O4 nanoparticles.When it is used as a magnetic solid phase extraction(MSPE)material,its unique properties such as large surface area,abundant functional groups,high adsorption capability,good enrichment effect and easy recovery make it stand out from other MSPE materials,and as a result,it has been applied in sample pre-treatments to achieve preconcentration of analytes at a trace level and improve the analytical performance of methods.In this research,MRGO magnetic nanocomposite was synthesized by one-pot solvothermal method and applied as MSPE adsorbent for extraction of pesticide residues and drug residues in food samples.We focused on the improvement on the extraction sensitivity and selectivity of MRGO through surface functionalization,and the elimination of the interference from fruits and vegetables.The main contents are described as follows:1 Surface modification of MRGO for the detection of clenbuterol hydrochloride in pig samplesIn order to improve the extraction efficiency of MRGO for clenbuterol hydrochloride(CLH),Lysine,KH-550 and adipic acid(AA)were introduced to modify MRGO,and the extraction results obtained by MRGO modified by different compounds were compared and the dosage of the best modifier was optimized.The results indicated that 15mg MRGO modified by 25mg of AA achieved the highest extraction capability.Subsequently,the successful modification was confirmed using Fourier transform infrared spectroscopy.Finally,MRGO@AA nanocomposite was used as an adsorbent and the parameters affecting the extraction performance of CLH was optimized by coupling MSPE with HPLC,including MRGO dosage,extraction time,concentration of salt and pH.Under the optimal conditions,a method for the determination of CLH was presented and the proposed method was linear in the range of 0.5-100?g/L with a coefficient of 0.9991,and the limit of detection was 0.027?g/kg;the relative standard deviation(RSD)of five replicates was 7.29%.This method was successfully applied to the analysis of OPPs in pig samples including pork and swine urine.The absolute extraction rate was 58.1%,which was higher than MRGO(33.8%).The recoveries under four spiked levels were in range of 89.2?101.3%,80.2?93.1%and 58.6-79.0%with RSD in the range of 3.4-10.5%,2.4-14.5%and 5.2-10.6%,respectively.2 Relevant research of extraction efficiency,sample matrices and physicochemical properties of analytesTo explore the enrichment capacity of MRGO for organophosphorous pesticides(OPPs)in real samples,the relationship between fruits and vegetables species,physicochemical properties of pesticides was studied.10 kinds of OPPs(phorate,diazinon,parathion-methyl,malathion,fenitrothion,durban,isocarbophos,methidathion,isofenphos-methyl,triazophos and methidathion)were selected as target analytes.Apple,pear,citrus,cowpea,cabbage,green pepper,cucumber,leek,broccoliand tomato were tested.The conditions affecting the extraction efficiency were optimized in the apple pulp(homogenated with apple and deionized water(w/w,1:2)).The results are as follow:20mL of apple pulp was diluted with 30mL of deionized water;25mg MRGO was used to extract for 30min;methanol and water(1:1,v/v)was chosen as a cleaning agent;3mL of acetone(three times,1mL for each time)was selected as a elute.Under those conditions,the extraction rates were the best,which ranged from 13.1?63.7%for all OPPs.Finally,the MRGO was used in 10 different fruits and vegetables to extract 10 OPPs.The results showed that the extraction rates of isocarbophos,parathion-methyl,isofenphos-methyl and triazophos were the highest,which ranged from 86.3?103.8%in water,and the first two varied from 21.5?79.3%while the latter two was lower than 14.5%in real samples;next was methidathion,with an extraction rate 74.4%in water while 9.7-53.9%in fruits and vegetables.The extraction rates of fenitrothion durban,diazinon,methidathion,phorate turned to be the worst,which varied from 31.1?58.5%in water and lower than 9.4%in real samples.In summary,MRGO tended to adsorb compounds containing benzene or C=O unsaturated bond,but the octanol-water partition coefficients of OPPs and the properties of matrices(pH,the contents of protein,pigmentum and insoluble dietary fiber)make differences to the adsorption capacity.In addition,the recyclability of MRGO was also explored and the adsorption rate changed below 10%when it was used no more than three times.3.Establishment of MSPE-GC method for the detection of OPPs based on MRGO nanocomposite in fruit and vegetables samplesIn this part,MRGO was used as an adsorbent to extract six OPPs from fruit and vegetable samples prior to gas chromatography-nitrogenphosphorous detection(GC-NPD).The extraction rates of ten OPPs showed no significant difference in different samples when 30mL of fruit pulps or vegetables pulps were diluted to 500mL.It proved that dilution could overcome the differences between matrices.In 500mL of diluted apple pulp,the best dosage of adsorbent was 25mg,the most appropriate extraction time was 40min,and the most suitable salt concentration was 2%.Under these conditions,a MSPE-GC-NPD method was established for the determination of six OPPs including diazinon,parathion-methyl,malathion,isocarbophos,methidathion,and triazophos.The results showed good linear ranges for six OPPs.The limits of detection(S/N=3)and limits of quantification(S/N=10)were from 0.45-1.9 ng/g and 1.6-6.3 ng/g,respectively.The relative standard deviations ranged from 4.02%to 7.63%.The proposed method was applied to five fruit and vegetable samples,and the recoveries of OPPs for spiked samples were ranged from 61.3 to 123.0%with RSDs below 14.7%.