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1. Principle of pesticide residue detection The principle of pesticide residue detection instrument is to use enzyme inhibition method under certain conditions. Organophosphorus and carbamate pesticides can inhibit the activity of cholinesterase, and the inhibitory rate is positively related to the concentration of pesticides 11-21. Under normal conditions, enzymes catalyze the hydrolysis of metabolites. The hydrolyzed product reacts with a color developing agent to produce a yellow substance, and the absorbance is measured at 410am with a spectrophotometer with time to calculate the inhibition rate, and whether or not there is a high dose of organic phosphorus in the sample can be judged by the inhibition rate. The presence of carbamate pesticides.
2, pesticide residue rapid measurement method
2.1 reagent preparation and preservation
2.1.1 Buffer. Using a graduated cylinder, measure 500 mL of distilled water, slowly pour in a small amount (100 to 150 mL) of distilled water into a measuring cup filled with a buffered dry powder, and stir until completely dissolved with a glass rod. Pour the remaining distilled water in the measuring cylinder into the measuring cup. Stir (shake) and wait.
2.1.2 color reagents. Use a graduated pipette to absorb 5.2 mL of buffer solution and inject it into the reagent bottle. Cover it with a cap and shake it. Place it in a 0-5 °C environment. Do not freeze.
2.1.3 Substrates. Use a graduated pipette to suck 5.2 mL of distilled water and inject it into the substrate dry powder bottle. Cover it with a lid and shake it. Place it in a 5 cc environment for use.
2.2 Preparation of the sample solution taken clean vegetables, with a balance accurately weighed 2 g, leaf blade portion taken, fruits and vegetables at a cross cut blade, cut flesh like I cm2, placed in a 100 mL beaker small; Pipette 10 mL of buffer solution into a small beaker and shake it for about 2 min. After the end of the extraction, allow it to stand for 2-3 min and take the supernatant as a sample solution.
2.3 Instrument Operation and Sample Determination
2.3.1 The instrument warms up. Turn on the power, the instrument self-test, after the end of self-test preheating 10 min. Measure 13-71 after the instrument is stable.
2.3.2 Control assay. Parallelism to the leftmost color detection plate hole with special pipette Bu were added 10 L of the enzyme reagent, and then 250 L pipette hopper suction hopper 250 L buffer start colorimetric vibration plate hole, press the arrow keys to select " Press the "Confirm" button after the menu to start the vibration plate 10 S, after the vibration plate is over. Let the enzyme reagent and buffer mixture stand for 10 min. Use a special pipette to add lO bucket L color reagent and 10 buckets of L substrate respectively to the colorimetric well. Immediately place the assay plate in the tray and press Key measurement (the reaction time is set to l min). At the end of the test, press "OK" to display the change in absorbance of the control. Absorbance change value to be blank control value in 0.15 plus. 30, can measure the sample. Otherwise, make a blank measurement again. After the measurement is completed, the instrument automatically saves the current control value. The next time the sample is measured,
2.3.3 Sample determination. If you have completed the control test for each channel, measure all the colorimetric wells on the assay plate as samples. Was added to each hole colorimetric different enzyme solution was pipetted 10 "L / hole, filling the sample liquid arm [250 / hole, a developer hopper lO L / hole. Test Procedure with the control, press the" Sample "button After the measurement, after the test is completed, the current measured sample inhibition rate result and absorbance change value are displayed, and the inhibition rate of the measured sample can be printed as required.
2.3.4 Determination of test results. Measurement results are expressed as inhibition rates. According to the GB/T 5009.199-2003 determination requirements, when the inhibition rate of the sample to the enzyme is ≥ 50%, it indicates that there is a high dose of organophosphorus or carbamate pesticide in the vegetables, and the sample is a positive result. Samples with positive results need to be measured more than two times.
3, matters needing attention
(1) Regularly calibrated and scientifically used pipettes. Use 250 buckets of L and 10 buckets of adjustable pipettes. Rinse the nozzle with clean water and rinse with pure water. Calibrate the amount of liquid absorbed on the electronic balance. When the pipette is used, it must follow the principle dedicated to the device: a pipette that sucks enzyme, color reagent, and substrate should be affixed with a special label, and when the reagent is removed, it should be used one by one.
(2) The test chamber temperature should be controlled at 20-25°C, otherwise it will affect the activity of the enzyme and affect the result deletion. If the instrument is turned off and restarted after the control measurement is completed, the control must be measured again. For control measurements, the change in absorbance of the control after 1 min should be above 0.15, otherwise the enzyme reagent cannot be used again.
(3) During the preparation of the sample solution, the extraction should be sufficient, and the shortening time has a greater impact on the results. The reaction time between the enzyme reagent and the sample solution or the buffer solution was 10 minutes. The reaction time was different and the results were different. Remove the reagent from the refrigerator and return to room temperature before use. Enzymes, color reagents and substrates cannot be added or added excessively, otherwise they have a great influence on the results. When reagents are used, they must follow the principle of no exit: reagents removed from enzymes, color reagents, and substrate reagent bottles. Do not return to the original reagent bottle to avoid contaminating the original reagent 151. If bubbles are detected in the cuvette under test Should be ruled out. In order to avoid affecting the measurement results.
(4) The inhibition rate A% of the measurement result is "one to one", indicating that the measurement result is invalid. This can be caused by several reasons: After the reagent is removed from the refrigerator, the control is not returned to room temperature; the control test time is too long apart from the sample test time. Causes the illumination and the sample to test the temperature condition to have the big difference; The test sample pigment interference is more serious; The reaction reagent takes the quantity to be accurate. In addition, other non-test hole blank holes may also appear "~ a" (four). When the instrument is operated, pay attention to the position of the hole in the tray can not have other foreign materials such as hair, cotton, etc. If there is dirt or liquid, clean it with filter paper so as not to affect the optical path measurement. The original records such as sample orders and test results should be organized and kept well.
(5) Samples with an inhibition rate of ≥ 50% should be tested at least twice. To determine whether this sample is qualified. Onion, garlic, radish, leeks, celery, parsley, mushrooms and tomato sap contained plant secondary biomass that had an impact on the enzyme, and 5 samples of pseudophosphorus pesticides were easily produced. The detection rate was 6.3%. The pesticides detected were acephate, chlorpyrifos, triazophos, and omethoate.
2.4 Test Results of Organochlorine Pesticide Residues As can be seen from Table 5, of the 80 samples tested, 3 were found to be organofluorine pesticides, and the detection rate was 3.8%. The pesticides detected were cyhalothrin, triadimefon, and chlorothalonil.
4. Introduction and discussion
(1) From the perspective of the detection recovery rate of the sample, the addition recovery rate is between 65% and 130%, which is in line with the relevant national standards.
(2) Organochlorine pesticides have been restricted and banned in some countries since the 1940s, starting in the 1980s and the 1980s. China stopped production samples in 1983. The results showed that there were guns in the specialty products in Bijie. Chlorine pesticides, but according to national standards, the samples were detected but not excessive, indicating that the special agricultural products in the Bijie area are safe. Organochlorine pesticides, some varieties of toxicity, have a certain degree of accumulation, the pesticides were also detected in the test, such as cyhalothrin, triadimefon, chlorothalonil. Therefore, it is necessary to strengthen the supervision of the use of such pesticides.
(3) Organophosphorus pesticides are highly effective, quick-acting, and broad-spectrum. They are often used as insecticides, and their actions mainly inhibit cholinesterase activity. Acephate, chlorpyrifos, triazophos, and omethoate pesticides were detected in this test sample. From the analysis of test results, these pesticides are detected, but the residue is much lower than the national limit standard, and will not cause any health indicators for specialty agricultural products in Bijie Prefecture.
(4) Through the detection of pesticide residues in specialty agricultural products in Bijie area and the comparison of pesticide residue limit standards in China's food, it is found that characteristic agricultural products in Bijie area have low pesticide residues and less pollution. However, pesticides were detected. It is hoped that related departments will strengthen supervision, strengthen the propaganda and guidance for the rational use of pesticides, standardize the agricultural capital market, and establish a sound market access system. Put an end to the sales of inferior agricultural products. Maintain the quality, safety, and reputation of the import and export trade of specialty agricultural products in the region. Ensure that the majority of consumers eat safe and reliable specialty agricultural products.
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