Study On Rapid Detection Method Of Organophosphorus Pesticides Residues In Vegetables

During the planting of vegetables, many kinds of pesticides are used to protect vegetables, so the problems of pesticides residues are very serious. Organophosphorus, synthetic pyrethroid and organic nitrogen pesticides are the main kinds of pesticides used in vegetables, among them organophosphorus pesticides residues are the most serious problems. Vegetables containing excessive organophosphorus pesticides will do harm to human health. Acute poisoning will cause spastic muscle, mydriasis, breath difficulty, and even death. Chronic poisoning will cause neuropathy, palsy, etc. So it's necessary to detect the pesticides residues in vegetables.A spectrophotometric method and detection system for rapid determination of organophosphorus pesticide is presented in this thesis. A complete assay could be performed in less than 15min. The assay displayed a detection limit of 0.5mg/kg of omethoate and dimethoate, and 1mg/kg of methamidophos. The main contents and results of this thesis are as following:1. Research on the detection of organophosphorus pesticides based on the method of alkali hydrolysis-phosphomolybdenumblue by spectrophotometer. The optimum experimental conditions are as following: Wave length of maximum absorption:700nm; quantity of alkali:4% NaOH 10mL; time of hydrolysis: 1 min, quantity of 3.75 mol/L sulfuric acid: 1.4mL, quantity of 2.769% ammonium molybdate:1.8mL;quantity of 2% stannous chloride: 0.1mL;time of coloring reaction: 10min. Linear regressive equation of pesticides: methamidophos: A = 0. 0033Cm+0.0001; omethoate: A = 0. 0003Co+0.0006; dimethoate: A = 0. 0006Cd+0.0012. The limits of detection: methamidophos: 1.6mg/kg;omethoate: 17.5mg/kg ; dimethoate: 8.7mg/kg. Sensitivity of detection: methamidophos: 0.0033mL.μg-1.cm-1 , omethoate: 0.0003mL.μg-1.cm-1 ,dimethoate: 0.0006mL.μg-1.cm-1.The coefficient of variation: methamidophos: 6.48%; omethoate: 7.02%;dimethoate: 6.15%。2. Research on the detection of organophosphorus pesticides based on the method of alkali hydrolysis-potassium permanganate by spectrophotometer. The optimum experimental conditions are as following: wave length of maximum absorption: 400nm, quantity of 1% NaOH: 10mL, time of hydrolysis: 1min,quantity of 3.75mol/L sulfuric acid: 0.3mL, quantity of 0.1% potassium permanganate: 0.1mL, time of coloring reaction: 5min. Linear regressive equation of pesticides: methamidophos: A = 0.0098 Cm -0.0024; omethoate: A= 0.0342 Co -0.0039; dimethoate: A= 0.0305 Cd -0.0084. The limit of detection: methamidophos: 0.5mg/kg;omethoate1: 0.1mg/kg;dimethoate: 0.2mg/kg. Sensitivity of detection: methamidophos: 0.0098mL.μg^-1.cm^-1 , omethoate: 0.0342mL.μg^-1.cm^-1 ,dimethoate: 0.0305mL.μg^-1.cm^-1. The coefficient of variation: methamidophos: 5.30%; omethoate: 3.71%;dimethoate: 5.78%.3. Contrast the method of alkali hydrolysis-phosphomolybdenumblue, the method of alkali hydrolysis-potassium permanganate with the method of the detection for total phosphorus. The method of alkali hydrolysis-phosphor molybdenumblue is not suited to determine the pesticides in low concentrations because the limit of detection of this method is not good. Recoveries of the method of alkali hydrolysis-potassium permanganate ranged from 92% ¹00%. Recoveries of the method of total phosphorus ranged from 93% ¹00%. So the method of alkali hydrolysis-potassium permanganate is suitable for the detection of organo- phosphorus pesticides.4. Determine the organophosphorus pesticides by the method of alkali hydrolysis-potassium permanganate and color sensor together. Three kinds of data processing methods, stepwise regression analysis, discriminant analysis, and general regression neural network, are used to establish the model between the value of color and the concentration of the pesticides. The accuracy rate of organophosphorus pesticides forecasted by stepwise regression analysis: methamidophos: 72.5%;omethoate: 86.7%;dimethoate: 88.3%.The accuracy rate of organophosphorus pesticides forecasted by discriminant analysis: methamidophos: 76.3%;omethoate: 100%;dimethoate: 100%. The accuracy rate of organophosphorus pesticides forecasted by general regression neural network: methamidophos: 81.4%;omethoate: 96.7%;dimethoate: 95.0%。The result shows: the accuracy rate of organophosphorus pesticides forecasted by general regression neural network generally exceeds 80%. So general regression neural network is selected as the data processing method for color sensor determining organophosphorus pesticides.5. Design the rapid determination system for organophosphorus pesticides residues. This system contains hardware and software. The hardware mainly includes: computer, color sensor, RS232 serial interface. The software is composed of four modules: serial communication, data determination, establishment of model and identification of the concentration of the sample. 6. Assay of organophosphorus pesticides in vegetables. Through the contrast among alumina, activated carbon and diatomite, 0.5g alumina is determined as the material of the cleanup column. Through the contrast of four kinds of elution solution: 20℃distilled water, 90℃distilled water, phosphate buffer solution and sodium chloride solution, recoveries of 20℃distilled water generally exceeded 70%. So 20℃distilled water is used as the elution solution of the vegetables. Comparing the effect of the elution effectiveness of different time, 5 min is chosen as the time of elution. At last, accuracy and precision of spectrometric method are compared with the method of rapid determining system. Recoveries of methamidophos and omethoate exceed 80%, and precision is within 10% by spectrometric method;Recoveries of omethoate are 100% by the method of rapid determining system, recoveries and precision of methamidophos are not good by the method of rapid determinging system because the sensitivity is low.