The Qualitative And Quantitative Analysis Of Pesticide Residue In Tea Using Surface-enhanced Raman Spectroscopy (SERS)

Surface-enhanced Raman spectroscopy (SRES) is increasingly used in the safetytest of food and agricultural products due to its characteristics as rapid analysis and highsensitivity of detecting. Currently China is one of the tea exporters, whose tea is with thehighest rate of overweight of pesticide residue. This thesis discusses the method ofqualitative and quantitative analysis of variety of pesticide residues in agriculturalproducts by applying the method of SERS rapid detection to tea. The protocol is asfollowing: detecting the residue of thiabendazole (fungicide, the maximum detectionlimit of1mg/L), chlorpyrifos (organophosphate insecticides, the maximum detectionlimit of1mg/L) and deltamethrin (organochlorine pesticides, the maximum detectionlimit of1mg/L) in dry and fresh tea leaves respectively. The discussion wills mainlycover three aspects: the study of method of qualitative and quantitative analysis ofthiabendazole residue in dry and fresh leaves by applying SERS rapid detection, the studyof method of qualitative and quantitative analysis of chlorpyrifos residue in dry and freshleaves by applying SERS rapid detection and the study of method of qualitative andquantitative analysis of deltamethrin residue in dry and fresh leaves by applying SERSrapid detection.(1) The study of method of qualitative and quantitative analysis ofthiabendazole residue in dry and fresh leaves by applying SERS rapid detectionFirstly, pigments, proteins, theanine, polyghenols and other fluorescent substancesin tea leaves should be removed by the use of iron oxide nanoparticles and carbongraphite. The substrate with best effect of enhancement in thiabendazole pesticide issilver nanoparticles by comparison of silver nanoparticles, gold nanoparticles andcommercial base OTR202. With the silver nanoparticles as the enhancement base, theSERSs of solid standard Thiabendazole, thiabendazole solution, thiabendazole solutionwith extract of dry tea as the substrate, thiabendazole solution with extract of fresh tea asthe substrate are collected. Three characteristic peaks of thiabendazole are identified,namely782,1007and1576cm-1through the calculation of spectroscopy by densityfunctional theory. Those three characteristic peaks are considered as the qualitativediscrimination basis for thiabendazole residue in tea because the peak782cm-1has thecharacteristic of outer vibration of the surface of C-H group of thiabendazole molecule;the peak1007cm-1has the characteristic of inside vibration of the surface of C-H groupthiabendazole molecule; the peak1576cm-1has the characteristics of ring vibration ofthiabendazole molecule and stretching vibration of C=N group. The detection capabilityof thiabendazole residue both in fresh tea leaves and dry tea leaves have reached1mg/L.Based on the peak intensity at782cm-1, a linear equation which is used to detect differentconcentration of thiabendazole residue with fresh tea extract as the substrate is established. The equation is y=348.49x+2711.8, the correlation coefficient: R2=0.9917.With the dry tea extract as the substrate, the equation is y=137.55x+9094.4, thecorrelation coefficient: R2=0.9966. The rate of recovery of thiabendazole pesticides infresh tea is88.16~95.93%, and the relative standard deviation (RSD) is between4.85~9.17%. The rate of dry tea is88.21~96.83%and the relative standard deviation(RSD) is between5.72~8.97%.(2) The study of method of qualitative and quantitative analysis ofchlorpyrifos residue in dry and fresh leaves by applying SERS rapid detectionWith the silver nanoparticles as the enhancement base, the SERSs of solid standardchlorpyrifos, chlorpyrifos solution, chlorpyrifos solution with extract of dry tea as thesubstrate, chlorpyrifos solution with extract of fresh tea as the substrate are collected.Five characteristic peaks of chlorpyrifos are identified, namely340、672、1095、126and1568cm-1through the calculation of spectroscopy by density functional theory. Those fivecharacteristic peaks are considered as the qualitative discrimination basis for chlorpyrifosresidue in tea. Among them, the spectral peak340cm-1is attributable to the deformationvibration of N-cyclopropyl; the peak672cm-1attributes to the ring breathing vibration ofchlorpyrifos molecule; peaks1095and1264cm-1are attributed to the surface deformationvibration of C-H group; peak1568cm-1is a co-frequency attributed to the joint action ofring vibration of chlorpyrifos molecule and the stretching vibration of C-C group. Thedetection capability of chlorpyrifos residue both in fresh tea leaves and dry tea leaveshave reached1mg/L. Based on the peak intensity at1095cm-1, a linear equation whichis used to detect different concentration of chlorpyrifos residue with fresh tea extract asthe substrate is established. The equation is y=17.943x+698.73, the correlation coefficient:R2=0.9905. With the dry tea extract as the substrate, the equation is y=2.5393x+413.57,the correlation coefficient: R2=0.9901. The rate of recovery of chlorpyrifos pesticides infresh tea is89.12~96.82%, and the relative standard deviation (RSD) is between1.65~8.75%. The rate of dry tea is85.26~96.95%and the relative standard deviation(RSD) is between2.09~3.84%.(3) The study of method of qualitative and quantitative analysis ofdeltamethrin residue in dry and fresh leaves by applying SERS rapid detectionWith the silver nanoparticles as the enhancement base, the SERSs of solid standarddeltamethrin, deltamethrin solution, deltamethrin solution with extract of dry tea as thesubstrate, deltamethrin solution with extract of fresh tea as the substrate are collected.Three characteristic peaks of deltamethrin are identified, namely997、1165and1202cm-1through the calculation of spectroscopy by density functional theory. Those threecharacteristic peaks are considered as the qualitative discrimination basis forthiabendazole residue in tea. Among them, the peak997cm-1is attributed to the outersurface deformation vibration of C-H group; the peak1165cm-1is attributed to the ring vibration of deltamethrin molecules; the peak1202cm-1is attribute to the stretchingvibration of P-O-C group. The detection capability of deltamethrin residue both in freshtea leaves and dry tea leaves have reached1mg/L. Based on the peak intensity at997cm-1, a linear equation which is used to detect different concentration of deltamethrinresidue with fresh tea extract as the substrate is established. The equation isy=36.286x+1461, the correlation coefficient: R2=0.9944. With the dry tea extract as thesubstrate, the equation is y=6.3053x+787.53, the correlation coefficient: R2=0.9884. Therate of recovery of deltamethrin pesticides in fresh tea is80.9~94.75%, and the relativestandard deviation (RSD) is between3.11~5.21%. The rate of dry tea is86.13~94.17%and the relative standard deviation (RSD) is between7.00~9.5%.The study of this thesis reveals that the method of surface-enhanced Ramanspectroscopy can be applied in the qualitative and quantitative detection of pesticideresidues in tea, which provides, which provides a quick and convenient method for thedetection of pesticide residues in tea in terms of rapid qualitative screening and initialquantitative detection.