Methods for the analysis of pesticide residues, methods for the detection of pesticide residues

Pesticide residue testing methodsThere are spectroscopy, enzyme inhibition, and chromatography.

1. Spectroscopy is based on the chemical reaction of oxidation, sulfonylation, complexation and other chemical reactions between certain functional groups or hydrolysis and reduction products in organophosphorus pesticides and special chromogenic agents in a specific environment to produce a color reaction of a specific wavelength to carry out qualitative or quantitative determination. The limit of detection is in the microgram range.

It can directly detect solid, liquid and gas samples, with low requirements for pretreatment of sample tong key products, low environmental pollution, and fast analysis speed. However, spectroscopy can only detect one or a class of organophosphorus pesticides with the same group, and the sensitivity is not high, and it can generally only be used as a qualitative method.

2. The enzyme inhibition method is based on the insect toxicological principle that organophosphorus and carbamate pesticides can inhibit the activity of acetylcholine in the insect center and peripheral nervous system, cause the accumulation of acetylcholine, a nerve conduction medium, affect normal nerve conduction, and cause insect poisoning to death. According to this principle, by reacting the specific inhibition of cholinesterase (CHE) with the sample extract, if the CHE is inhibited, it indicates that the sample extract contains organophosphorus or carbamate pesticides.

3. Chromatography is one of the common methods for pesticide residue analysis, which achieves the purpose of separation according to the different partition coefficients of the analyzed substances between the stationary phase and the mobile phase, and converts the concentration of the analyzed substances into electrical signals (voltage, current, etc.) that are easy to be measured, and then sends them to the recorder to record them. There are mainly thin layer chromatography, gas chromatography and high performance liquid chromatography.

Rapid Detection Technology:

However, the traditional GC MS and other pesticide residue analysis technologies have high cost and long time, which has brought a lot of inconvenience to the food safety supervision department to the supervision of agricultural products before, during and after production, so it has also given rise to a large number of rapid pesticide residue detection technologies, such as chemical rapid detection method, immunoassay method, enzyme inhibition method and in vivo detection method.

1. The chemical rapid measurement method is mainly based on the redox reaction, the hydrolysate and the detection solution change color, and is used for the rapid detection of organophosphorus pesticides, but the sensitivity is low, the use is limited, and it is easy to be interfered by reducing substances.

2. Immunoassay method, mainly including radioimmunoassay and enzyme immunoassay, the most commonly used is enzyme-linked immunoassay (ELISA), based on the specific recognition and binding reaction of antigens and antibodies, for small molecular weight pesticides, artificial antigens need to be prepared in order to carry out immunoassays.

3. The enzyme inhibition method is the most mature and widely used rapid pesticide residue detection technology, which is mainly based on the specific inhibition reaction of organophosphorus and carbamate pesticides on acetylcholinelinease.

4. The liveness detection method mainly uses the sensitive reaction of living organisms to the pesticide residues, such as feeding samples to houseflies and observing the mortality rate to determine the amount of pesticide residues. The method is simple to operate, but the qualitative is rough, the accuracy is low, and the scope of application to pesticides is narrow.

<>1. Definition: Pesticide residues refer to the phenomenon that some pesticides remain in grains, vegetables and fruits, livestock products, aquatic products, soil and water bodies after the use of pesticides in agricultural production. 2. Classification of residual pesticides:

According to the residue characteristics, it is divided into three categories, namely plant residual pesticides, soil residual pesticides, and water residual pesticides. 3. Residual form: it is divided into two types, one is to maintain the original chemical structure, and the other is the form of chemical transformation products or biodegradation products.

1. The nature of pesticide residues

1. Pesticide residues refer to the phenomenon that some pesticides are directly or indirectly left in grains, vegetables and fruits, animal products, aquatic products, soil and water bodies after the use of pesticides in the agricultural production process.

2. Residual pesticides can be divided into three categories according to the residue characteristics, namely plant residual pesticides (easy to remain in plant organisms), soil residual pesticides (easy to remain in the soil), and water residual pesticides (long-term residues in water bodies).

3. There are two main forms of residual pesticides in plants, soil and water, one of which is to keep the original chemical structure unchanged, and the other is to remain in the form of chemical transformation products or biodegradation products.

4. The influencing factors of pesticide residues mainly include the properties of pesticides themselves, environmental factors (including temperature, light, rainfall, soil pH, organic matter content, microbial content, etc.), pesticide use methods, etc.

Second, what components are mainly detected for pesticide residues

1. At present, in China's pesticide market, organophosphorus insecticides, carbamate insecticides, and pyrethroid insecticides are the three most important insecticides, so the main detection components of pesticide residues are organophosphorus, carbamate and pyrethroids.

2. The rapid detection methods of pesticide residues are mainly divided into two categories according to the principle, namely biochemical determination method and chromatographic detection method.

3. The biochemical assay method mainly uses the biochemical reaction of a certain biochemical substance extracted from the organism to judge the pesticide residue and pollution. Among these detection methods, enzyme inhibition and enzyme-linked immunoassay are widely used.

4. The chromatographic detection method is mainly to analyze the pesticide residues in vegetables and fruits by simplifying the purification steps of the sample as much as possible and directly extracting the sample.

1. Extraction method:

The immersion purification method is also known as the immersion method. For the extraction of a substance from a solid mixture or organism, the extraction agent used should be able to dissolve the extracted substance in large quantities without destroying the properties of the extracted substance.

2. Solvent extraction:

Solvent extraction is used to extract a component from a solution, and use the different partition coefficients of the component in two immiscible reagents to transfer it from one solution to another, so as to separate from other components to achieve the purpose of separation and enrichment.

3. Salting-out method.

Adding some inorganic salt to the solution makes the solubility of the solute in the original solvent greatly reduced, and precipitates out of the solution, this method is called salting-out. For example, a large amount of salts (ammonium sulfate) are added to the protein solution, especially heavy metal salts, so that the protein is precipitated out of the solution.

4. Extraction method.

Extraction is a unit operation that uses the principle of similar dissolution to separate mixtures by dispersion of different components in the system shed with different solubility in the solvent, and can be divided into extraction method (solid-liquid extraction) and extraction method (liquid-liquid extraction) according to the different components extracted. Extraction method (liquid-liquid extraction method): the extracted components are separated by different partition coefficients in two solvents that are immiscible with each other.

5. Decompression concentration method.

Some components to be tested are thermally unstable and easy to decompose at higher temperatures, and the use of reduced pressure concentration reduces the boiling point of the solvent, which can not only quickly concentrate to the required volume, but also avoid the decomposition of the analyte.

The commonly used decompression concentrator is the all-glass decompression concentrator, also known as the K-D concentrator, which is a commonly used decompression distillation device, which has the characteristics of low concentration temperature, fast speed, less loss and easy control of the required volume, and is suitable for the concentration of thermally unstable analyte extracts, especially for the concentration of sample solutions in the analysis of pesticide residues. In addition, it can also be used for purification and distillation of solvents.