Pesticide residue refers to any specific substance that occurs in food, agricultural products and animal feed as a result of the use of pesticides, including pesticide derivatives that are considered to have toxicological significance, such as pesticide transitions, metabolites, reaction products and impurities. Pesticides are directly or indirectly applied to the food, vegetables, fruits and other agricultural products that people rely on for survival and farmland, and more or less stored in them, forming pesticide residues in plant foods. Some pesticides are quite stable in the environment, the residue period is long, coupled with repeated use, the accumulation in the environment increases, and through the role of the food chain, the enrichment in the animal body, the formation of pesticide residues in animal food.

Pesticide residues are related to food safety, is an important food detection project, at present, there are a variety of detection methods in food residues, in addition to the most commonly used chromatography mass spectrometry, as well as spectroscopy, capillary electrophoresis, immunoanalysis and enzyme suppression methods and other detection technologies. The following Xiaobian will give you a detailed introduction.

Detection method of pesticide residue standard substances in food:

1. Spectroscopy

The method is based on organophosphorus pesticides in some functional groups or hydrolysis, reduction products and special color development agent under specific conditions of oxidation, sulfonic acid, esterification, complexation and other chemical reactions, resulting in specific wavelength color reaction for qualitative or quantitative (limited) determination.

2. Chromatography

(1) Thin Layer Chromatography (TLC)

Thin layer chromatography (TLC) is a mature and widely used method for rapid detection of trace. It has its unique use in pesticide residue determination technology, which is not only an important separation means, but also a qualitative and quantitative analysis method.

In the detection process, organophosphorus pesticides are generally extracted with appropriate solvents, purified and concentrated, separated on a thin layer of silica gel plate, and compared with the standard organophosphorus pesticides after color development for qualitative determination or quantitative determination with instruments.

(2) Gas Chromatography (GC)

In this method, the extracted, purified and concentrated organophosphorus pesticides are injected into a gas chromatography column, and after the programmed temperature rise and vaporization, different organophosphorus pesticides are separated in the solid phase, and the gas chromatogram is described by different detectors. The retention time is qualitative, and the peak or peak area is compared with the standard curve for quantitative analysis. Multiple components can be measured at the same time, simple and fast, high sensitivity, and good accuracy. The optimum setting of chromatographic conditions is the key of gas chromatography technology.

(3) High Performance Liquid Chromatography (HPLC)

High performance liquid chromatography (HPLC) is a chromatographic analysis method developed by introducing gas chromatography theory and improving it on the basis of liquid chromatography column chromatography. High performance liquid chromatography (HPLC) is more and more widely used in pesticide residue analysis because it is suitable for analyzing high boiling point and not easy to vaporize, heat unstable and strong polar pesticides and their metabolites.

It can be combined with pre-column extraction, purification, post-column fluorescence derivatization and mass spectrometry, and easy to realize automatic analysis. At the same time, the advent of some new detectors has improved the detection sensitivity of HPLC to a certain extent. Compared with gas chromatography, it not only has good separation efficiency, high sensitivity, fast detection speed, but also has wide application.

3, chromatography-mass spectrometry combined usage

Chromatography-mass spectrometry technique not only plays the high separation ability of chromatography, but also plays the high discrimination ability of mass spectrometry. It can be used for qualitative and quantitative analysis of multiple residues when they exist at the same time, especially for multi-residue analysis. Gc-ms is a relatively mature and widely used color mass coupling technology. It not only has the high separation performance of gas chromatography, but also has the characteristics of accurate identification of compound structure by mass spectrometry, which can achieve the purpose of qualitative and quantitative detection at the same time, and is mostly used for the detection of pesticide metabolites, degradants and multi-residue detection.

4. Capillary electrophoresis

In the past, pesticides were determined by HPIE and GC, but recently CE separation can be used. The main separation modes were CZE and capillary micellar electrokinetic chromatography (MEKC). Capillary electrophoresis has been used to determine pesticide residues in milk, beer, cereal, fruits, vegetables and pork.

5. Immunoassay technology

Radioimmunoassay and enzyme immunoassay are used in pesticide residue detection. At present, the application of enzyme immunoassay, especially enzyme-linked immunoassay, in pesticide residue detection is very active in foreign countries, and its application is becoming more and more common. ELISA is a detection method based on the specific and reversible binding reaction of antigen and antibody, and its detection level can reach ng or pg level.

ELISA is widely used in the analysis and detection of pesticide residues in food, such as organophosphorus pesticides, organochlorine pesticides, herbicides, carbamate pesticides, veterinary drug residues (such as chloramphenicol), mycotoxins. As a rapid screening method, EKSIA often has the problem of false positives in the analysis of complex matrix samples because of matrix interference and cross-linking reaction. Therefore, other analytical methods are required if the sample needs to be quantified and confirmed.

6. Enzyme inhibition method

Enzyme inhibition method is the most studied and relatively mature technology for the rapid detection of some pesticide residues. The most commonly used enzyme inhibition method for pesticide residue determination is acetylcholinesterase, which is sensitive to organophosphorus pesticides, has high sensitivity and strong selectivity, but it is expensive, and some pesticides do not have obvious inhibition on it, so additional oxidation additives or pretreatment are needed to improve the sensitivity of pesticide detection.

Therefore, some studies have been conducted to replace acetylcholinesterase with buylcholinesterase and animal and plant esterase. By screening a large number of plants, Yu Jicheng et al. initially obtained plant enzyme sources with high activity, and quickly detected organophosphorus pesticide residues such as trichlorfon and parathion in vegetables by enzyme inhibition method.

7. Biosensors

Organophosphorus and carbamate pesticide residues were determined by a biosensor assembled with immobilized AChE film and pH electrode. At present, the development and application of biosensor method is a research hotspot in pesticide residue detection technology, and great progress has been made in diversifying measurement methods, improving measurement sensitivity, shortening response time, improving instrument automation and adapting to field detection capabilities.

The biological substances used in the biosensor for the detection of pesticide residues are mainly enzymes, whole cells, organelles, receptors or antibodies, etc. The corresponding enzyme sensors, whole cell sensors and immune sensors, especially the application of immune sensors can greatly improve the detection sensitivity and greatly shorten the detection time. The combination of biosensor and optical fiber technology, optical fiber sensor, has a broad application prospect in rapid detection and online detection.

8. Biopsy method

Bioassay is a technique that uses living organisms to perform bioassays. For example, after the interaction between pesticides and bacteria, the luminous intensity of bacteria can be affected, and the luminous intensity of bacteria can be used to detect pesticide residues. However, the method can only respond to a few pesticides, and can not identify the types of residues, and the accuracy is low. The detection method of sensitive housefly is to feed the sample to the housefly and determine the pesticide residue according to the mortality rate of the housefly.

The technique is direct, simple and easy to master, and users can detect themselves without complex instruments. The disadvantages are that the detection time is long, the qualitative quality is rough and the accuracy is low, and it is only effective for a few pesticides. Moreover, because the toxic reaction of other organisms to different pesticides may be different from that of humans and animals, it affects the judgment of pesticide residues.

The above content is the introduction of the detection method of pesticide residues in food standard substances, the threat of pesticide residues in food to human health can not be ignored, so the world in the development of efficient and safe pesticides at the same time, also pay attention to the existing use of pesticides in food residue control, the formulation of residue limit indicators, in order to ensure food safety and maintain human health.