The Application Research Of Functionalized Graphene In Food Safety Monitoring Based On Solid-phase Microextraction

Solid phase microextraction (SPME) is a sample preparation technique which integratessampling, extraction, enrichment and injection in a single step. And the SPME technique isconducive to the environment. SPME can be characterized as a simple, solvent-free(or using asmall amount of solvent) and low detection limits method. So it has been widely used in the fieldof food safety testing, environmental monitoring and drug analysis. Nowadays, the food problemhas become a serious threat to human health, because more and more vendors add food dyes freelyto improve the appearance of the food. Also, the farmers use various pesticides during the growthof the fruits and vegetables which lead to the pesticide residue. Hence, it is important to strengthenfood safety monitoring. The fiber coating is considered to be the key factor in the SPME technique.However, there are many shortcomings in the commercial polymer coatings of SPME fibers, suchas possibility of swelling in some organic solvents, easy peeling off and bad selectivity. Therefore,it appears to be very important of developing a kind of coating with low cost, high stability andselectivity. The functionalized graphene becomes the preferred new and efficient micro-extractionmaterials for unique properties.1Adsorption-decolorization of four ionic dyes by carboxylated grapheneThe synthetic carboxylated graphene(G-COOH) was performed using the FTIR technique andused as an adsorbent for the solid-phase microextraction of methyl violet, neutral red, brilliantyellow and alizarin red in aqueous solution. The adsorption of four ionic dyes onto G-COOH wasstudied in a batch system with respect to adsorbent dose, contact time, initial dye concentration andsolution pH. Results showed that the dye adsorption capacity of G-COOH is closely related to thetype of dye, the adsorption capacity of cationic dye is significantly greater than anionic dye. Batchkinetic data from experimental investigations on the removal of four ionic dyes from aqueoussolutions fit well with the pseudo-second-order kinetic model. The Langmuir model agrees very well with the experimental data of cation dyes, while the adsorption behavior of anion dyes is fittedto Freundlich isotherms. The desorption data show that the removal percent of dye methyl violetfrom G-COOH is88.2%by using NaOH/EtOH eluting reagent, and the desorbed G-COOH can bereused to adsorb the dyes.2Preparation of carboxyl graphene solid phase microextraction coating and itsadsorption properties of methylene blueA novel carboxyl graphene-coated solid phase microextraction (SPME) fiber was prepared byimmobilizing the synthesized carboxyl graphene (G-COOH) on a stainless steel wire. And the fiberwas used for solid phase microextraction of methylene blue coupled with ECL determination. Thenew fiber was verified by SEM which showed that it possessed a homogeneous, porous andwrinkled surface. Under the optimized conditions (sample solution pH, extraction time, stirring rate,desorption time and desorption solvent), the method showed a good linear relationship in the rangeof2.7×10-9~1.3×10-6mol/L and the detection limit (S/N=3) was8.9×10-10mol/L.Thecarboxyl graphene-coated SPME fiber was successfully applied to the analysis of MB in drinkingwater samples, the recoveries ranged from95.7%to113.0%, and the relative standard deviations(RSD) were less than5.0%, which showed good reproducibility.3Preparation of magnetic amine-modified graphene for the extraction ofbifenthrinAmine-modified graphene magnetic nanocomposite（G-NH2/Fe3O4）was synthesized andused as an adsorbent for the solid phase microextraction of bifenthrin, coupled with HPLCdetermination. SEM、 FT-IR and X-ray diffraction were used to investigate the surfacemorphology and chemical character of G-NH2/Fe3O4. The influencing parameters of the samplepreparation method, such as eluant and leacheate, extraction time, desorption time, ionic strength,pH of sample solution, amount of adsorbent were systematically optimized prior to high liquidchromatography detection. The adsorption capacity of bifenthrin on modified graphene inferredfrom the Langmuir model was125mg/g at293K. Under the optimized conditions the methodshowed a good linear relationship in the range of0.005~10μg/mL, and the low detection limit(S/N=3) was1.7ng/mL. The recoveries of medlar spiked with bifenthrin was91.8%~101.6%, and the RSD was3.5%~4.2%; The recoveries of tap water spiked with bifenthrin was88.6%~96.7%, and the RSD was3.4%~4.3%. It was found that the elution rate of bifenthrin up to90.5%by using1%acetic acid/acetonitrile eluting reagent when elution duration was20min, and thedesorbed G-NH2/Fe3O4can be reused.4Sensitive electrochemiluminescence determination of carbaryl based onsolid-phase microextraction at NH2-graphene-Nafion modified electrodeIn this study, amine-modified graphene-Nafion (NH2-G-Nafion) modified electrode wasprepared and used for the solid phase microextraction of carbaryl. Its surface was characterized bySEM, and cyclic voltammetry and electrochemical impedance spectroscopy were performed tostudy its electrochemical properties. Under the optimized conditions (the buffered solution pH,extraction time and the sample solution pH), the method showed a good linear relationship in therange from5×10-4mg/L to10mg/L, and the low detection limit (S/N=3) was2×10-4mg/L. Theelectrochemiluminescence (ECL) sensor was successfully applied to the selective and sensitivequantitative determination of carbaryl in tomato, the recoveries of carbaryl ranged from99.0%to108.0%, and the RSD was less than5.0%. The RSDs of intra-assay and inter-assay were found tobe3.5and5.3%, respectively, and the peak current retained97%of its initial response current aftera10-day storage, indicating a nice storage stability and an acceptable reproducibility of the sensor.