Method and principle of pesticide residue detection

Detection principle and use method of portable rapid pesticide residue detector and card

Portable rapid pesticide residue detector is an instrument specially designed according to the national standard method GB/T5009. 199—2003. It is mainly used for the rapid detection of organophosphorus and carbamate pesticides in fruits, vegetables, tea, grain, water and soil, especially for the rapid detection of agricultural products quality inspection stations, on-site detection of fruits and vegetables production bases and professional households before picking, and the wholesale of agricultural products.

Detection principle:

The detection principle of the instrument is that the cholinesterase in the card (card ②) can catalyze the hydrolysis of indophenol acetate (card ①) into acetic acid and indophenol. Because organophosphorus and carbamate pesticides have a strong inhibitory effect on cholinesterase activity, the residue of organophosphorus or carbamate pesticides in samples can be judged according to the different color development.

How to use:

(1) Press and hold the "On/Off" key on the panel for about 2 seconds, and the instrument will be turned on (press the second key to turn it off): press the [Mode] key to switch to "Temperature". When the temperature reaches 40℃, the instrument will give a prompt sound and the test can be started.

(2) Assemble the quick test card, tear off the upper cover film, fold it in half, and then unfold it. Insert it into the heating plate of each channel under the batten (note that one end of card ① is above and the other end of card ② is below), and check whether the quick test card is placed correctly. The dotted line in the middle of the quick check card should be aligned with the layering and not skewed.

(3) Sampling representative vegetables or melon peels, wiping off the surface soil, cutting into pieces of about one square centimeter, putting 5g into a bottle with a lid, adding 10 ml purified water or buffer solution, shaking evenly for 50 times (stirring with an ultrasonic cleaner if necessary), and standing for more than 2 minutes. It is best to make 9 samples in each batch, and make a blank control of purified water or buffer at the same time. After cutting each sample, clean the sharp knife before handling another sample to avoid cross-contamination. Pipette 80 microliters of the sample solution and add it to the white tablet. If the test is carried out at the sampling site or under poor conditions, 2-3 drops of eluent can be directly dropped on the tip of the vegetable to be tested, and the tip of another vegetable leaf can be gently rubbed at the dropping point, so that the pesticide remaining on the surface of the vegetable can be fully dissolved in the lotion. Then drop a drop on (card 2).

(4) Press the key to test, and the reaction starts to count down 10 minute (the "reaction" indicator light is on). When you hear the rapid buzzer sound from the instrument, close the cover, and the color development countdown starts for 3 minutes (the "color development" indicator light is on): when the instrument emits a slight buzzer sound, open the cover of the instrument to judge the result. If the result judgment is compared with the blank control card, it is judged. Strong positive results indicate high pesticide residues, while weak positive results indicate low pesticide residues. (Card ②) turns orange or is the same as the blank control card, which is a negative result. In addition, it means that this method is a biochemical reaction and some physical and chemical factors should be avoided as much as possible. The optimum pH value of the reaction is about PH7.5. When the sample is slightly acidic or alkaline, phosphate buffer should be used for leaching. During the reaction. The surface of tablets should be kept moist, and it is best to add samples evenly after each batch of samples is treated to avoid drying due to too long evaporation time. The juice of onion, garlic, radish, celery, water bamboo, mushroom and tomato contains plant secondary substances that affect enzyme activity, which is easy to produce false positive. When processing such samples, it is not appropriate to cut them into pieces, and the extraction time is too long. In order to avoid the influence of excessive juice release on the test results, the whole vegetable can be extracted if necessary. The validity period of pesticide quick test card is one year at normal temperature, and it should be kept in a cool, dry and dark place, and it is best to put it in a refrigerator at 4℃ if possible. It is best to use it up within three days after opening. If you can't use it all at once, you can store it in the dryer. The rapid detection card for pesticide residues in fruits and vegetables is an enzyme test paper made of cholinesterase and chromogenic agent which are highly sensitive to pesticides. It can quickly detect the residues of organophosphorus and carbamate, two pesticides with large dosage and great toxicity. The selected enzyme is sensitive to methamidophos, has strong anti-interference and simple operation, and can be used independently without preparation of reagents, professional technical training and any instruments and equipment.