How to detect pesticide residues in fruits and vegetables?

With the improvement of living standards, people pay more and more attention to dietary safety. As an important part of daily diet, fruits and vegetables have also attracted much attention to the problem of pesticide residues on their surface. How to accurately detect pesticide residues and make the food on the table more at ease? The following 5 practical detection methods, from rapid screening at home to accurate analysis in the laboratory, are introduced to you one by one.

1. Rapid detection test strip method: the first choice for convenient screening at home

This method is similar to the early pregnancy test strip we are familiar with. The principle is based on the specific binding of antigens and antibodies. The operation is simple: take a small amount of cleaning liquid on the surface of fruits and vegetables or cut a small amount of samples directly, add matching extract, shake and drop it on the test strip, and wait for a few minutes. If the specified color band appears on the test strip, it indicates that there may be The advantage is that no professional equipment is required, and the results can be produced in 5-10 minutes, which is suitable for rapid preliminary screening at home, in the market, etc.; but the disadvantage is that the accuracy is limited, and false positives or false negatives may occur, which needs to be verified in combination with other methods.

Second, colloidal gold immunochromatography: "right-hand man" for semi-quantitative detection

This is an upgraded version based on rapid detection test strips. The antibody is labeled with colloidal gold particles, and the semi-quantitative analysis of pesticide residues is realized through the principle of chromatography. When in use, the treated sample liquid is dripped into the detection card. After the target is combined with the colloidal gold-labeled antibody, it is moved to the detection line under the action of chromatography. The residual concentration is judged by the color depth of Compared with ordinary test strips, it can give more accurate results of "exceeding/not exceeding the standard" or "low/medium/high residue". It is suitable for small laboratories or mobile detection scenarios. It is a common tool for market supervision and small growers.

III. Enzyme inhibition method: rapid detection for organophosphorus pesticides

Organophosphorus pesticides (such as dichlorvos, digol, etc.) can inhibit the activity of cholinesterase. Enzyme inhibition method takes advantage of this property. Operation steps: Take samples (usually vegetables), extract them with buffer, add cholinesterase and substrate (such as DTNB), and react at 37 ° C for 15-30 minutes at constant temperature. The amount of product generated by the reaction of the substrate is detected by an enzyme labeling instrument. If the enzyme activity is inhibited by more than 50%, it indicates the presence of organophosphorus pesticide residues. This method has high sensitivity to organophosphorus pesticides, short detection time (about 30 minutes), low cost, and is suitable for rapid sampling in vegetable bases and farmers' markets.

IV. Gas Chromatography (GC): The "Gold Standard" for Accurate Quantification in the Laboratory

For scenarios that require accurate quantification, gas chromatography is a "routine operation" in the laboratory. Its principle is to extract and purify the pesticide residues in the sample, separate different substances through a gas chromatography column, and then detect them by detectors (such as electron capture detectors, hydrogen flame ionization detectors, FID). Due to the different retention times and signal strengths of different pesticides in the chromatographic column, a variety of pesticides can be accurately identified and quantified, and even residues at the ppb (parts per billion) level can be detected. The advantage is that the sensitivity is extremely high and the specificity is strong; but the disadvantage is that the equipment is expensive, the operation requires professional training, and the detection time is long (usually 1-2 hours), which is suitable for factory testing in large laboratories and food enterprises.

V. High-performance liquid chromatography (HPLC): a "good helper" for the detection of polar pesticides

Unlike gas chromatography, high-performance liquid chromatography is suitable for the detection of pesticides with strong polarity and poor thermal stability (such as urethane esters, some herbicides). It pushes the column of the mobile phase through a high-pressure infusion system. The difference in the distribution coefficient of pesticides in the sample between the stationary phase and the mobile phase is separated, and then detected by ultraviolet detector, fluorescent detector, etc. HPLC can not only detect a variety of polar pesticides, but also analyze multiple components at the same time. It is one of the most widely used methods in the detection of pesticide residues at present. It is especially suitable for the analysis of complex matrix samples (such as juice and fruit).

Summary: Choose a suitable detection method to protect the safety of diet

Different detection methods have their own advantages: Rapid detection methods (test paper, colloidal gold, enzyme inhibition) are suitable for preliminary screening and on-site detection. Laboratory methods (GC, HPLC) are the guarantee of accurate quantification. In daily life, in addition to professional testing, we can also reduce pesticide residues by soaking in water, rinsing with running water, peeling, etc., and give priority to fresh fruits and vegetables purchased through regular channels to make the diet more at ease.