Rapid Detection of Organophosphorus and Carbamate Pesticide Residues in Vegetables
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Over the years, pesticide residues in vegetables have been exceedingly prominent, and pesticide poisoning events have often been reported. One reason is that farmers do not apply pesticides according to the prescribed dosage, frequency, method or safety interval, or use highly toxic and highly toxic pesticides that are not allowed to be used on vegetables; With organic solvent extraction, purification, and use of large-scale analytical instruments, the lack of supervision of inexpensive vegetables that can be detected anytime, anywhere, or quickly becomes inadequate. Strengthening the propaganda guidance for farmers and establishing a standardized method for the rapid detection of pesticide residues suitable for China's national conditions is the key to solving the problem. Currently used pesticides can be roughly classified into the following categories according to their chemical structure: organochlorines, organophosphorus, carbamates, pyrethroids, etc. Among pesticides in China, 70% are organophosphorus pesticides. Of the organophosphorus pesticides produced and used in China, 70% are highly toxic and highly toxic, and many are banned from use on vegetable crops. Based on the above circumstances, a rapid detection method for organophosphorus and carbamate pesticides has been formulated so that it is not limited by time, location, and occasional conditions, and even ordinary consumers can operate and use it, facilitating the timely detection of problems and taking measures. Control the intake of high-residue pesticides, reduce the incidence of pesticide poisoning, and protect the safety of food for consumers. This test method has been adopted by the National Standards Committee and has been upgraded to the national standard rapid test method GB/T5009.199. Method 1 Quick Test Card Method 1 Scope This standard specifies that the organophosphorus and carbamate pesticide residues in vegetables are determined by enzyme inhibition method The rapid test method for quantity. This standard applies to the rapid screening and determination of organophosphorus and carbamate pesticide residues in vegetables. Principle 2 Cholinesterase catalyzes the hydrolysis of indophenol acetate (red) to acetic acid and indole phenol (blue), organophosphorus or urethane pesticides inhibit cholinesterase, catalyzes, hydrolyzes, and discolors The process changes to determine if the sample contains organic phosphorus or carbamate pesticides. 3 Reagents 3.1 A piece of paper with cholinesterase and nonylphenol acetate reagents (fast test card) cured. 3.2 pH7.5 buffer solution: Take 15.0g of disodium hydrogen phosphate [Na2HPO4·12H2O] and 1.59g of anhydrous potassium dihydrogen phosphate [KH2PO4], and dissolve with 500mL of distilled water. 4 Instrument 4.1 Constant balance equipped with 37 °C ± 2 °C thermostat device 5 Analysis steps 5.1 Overall determination method 5.1.1 Select a representative vegetable sample, wipe the surface mud, cut into pieces of about 1cm square, take 5g into In a capped bottle, 10 mL of a buffer solution was added, shaken 50 times, and allowed to stand for more than 2 minutes. 5.1.2 take a quick test card, pick up the extract with a white tablet, placed more than 10 minutes for pre-reaction, conditional when placed in a 37 °C constant temperature device for 10min. The pre-reacted tablet surface must remain moist. 5.1.3 Half-fold the speed test card, pinch it for 3 minutes by hand or thermostat for 3 minutes to allow the red pill to overlap with the white pill. 5.1.4 A blank control card for each batch of assay should be set up. 5.2 Surface Determination Method (Rough Sieving Method) 5.2.1 Wipe off the dirt on the vegetable surface, dripping 2 to 3 drops of the buffer solution on the surface of the vegetables, and gently rubbing with another piece of vegetable in the dropping place. 5.2.2 Take a quick test card and drop droplets of vegetables on white tablets. 5.2.3 Pre-react for more than 10 minutes, and place it in a 37°C constant temperature device for 10 minutes when conditions are met. The pre-reacted tablet surface must remain moist. 5.2.4 Half-fold the speed test card, pinch it for 3 minutes by hand or thermostat for 3 minutes to allow the red pill to overlap with the white pill. 5.2.5 A blank control card for each batch of assay should be set up. 6 The results were judged as the result of the enzyme being inhibited (positive) and not inhibited (negative) by organophosphorus or carbamate pesticides. Compared with the blank control card, the white tablets did not change color or slightly bluish blue as positive results. The white pill turns sky blue or the same as the blank control card and is a negative result. For samples with positive results, other analytical methods can be used to further determine the specific pesticide species and content. 7 Annex 7.1 Speed ​​Test Card Technical Specifications 7.1.1 Sensitivity Indicators: The detection limit of some common pesticides and the limited standards in China are shown in Table 1.
Table 1 Detection limits (mg/kg) and maximum residue limits (mg/kg) of some common pesticides
Name of pesticide
The detection limit
Residue limit
Name of pesticide
Detection limit
Residue limit
Methamidophos
1.7
No inspection
Dichlorvos
0.3
0.2
Parathion
1.7
Do not check out
Trichlorfon
0.3
0.1
Isocarbophos
3.1
Do not check out
Dimethoate
1.3
1.0
Malathion
2.0
Do not check out
Sevin
2.5
2.0
Monocrotophos
2.5
Do not check out
Good year winter
1.0
Do not check out
Acephate
3.5
0.2
Carbofuran
0.5
Do not check out
7.1.2 Compliance rate: Among the more than 30 positive samples detected, the compliance rate of positive results should be above 80% after gas chromatography verification. 8 Explanatory Notes 8.1 Sprouts, vegetable oils, radishes, leeks, celery, coriander, coriander, mushrooms, and tomato sap contain plant secondary substances that have an effect on the enzyme and are prone to false positives. When dealing with such samples, whole vegetable (body) vegetables may be used for leaching or surface determination. For some vegetables with high chlorophyll content, the whole plant (body) vegetable extraction method can also be adopted to reduce the interference of pigments. 8.2 When the temperature is lower than 37°C, the speed of the enzyme reaction is slowed down. The reaction time after the tablet is added should be relatively extended. To determine the extended time, use a blank control card (body temperature) to pinch for 3 minutes. Can be blue, you can go down. Note that the sample placement time should be consistent with the time of blank control card placement. The reason why the blank control card does not change color is as follows: First, the buffer solution on the surface of the tablet is added less, the surface of the tablet after the pre-reaction is not sufficiently moist, and the temperature is too low.