Experimental residue analysis of pyrethroid insecticides

Summary

Pyrethroids are an important class of synthetic insecticides with high efficiency, broad-spectrum, low toxicity and easy biodegradation. Source: Food Safety Testing Technology (Chemical Industry Press)

Operation method

Residue analysis of pyrethroid insecticides

Principle

Pyrethroids are an important class of synthetic insecticides that are highly effective, broad-spectrum, low-toxic and readily biodegradable. One of the common features of pyrethroids in their chemical structure is that the molecular structure contains several asymmetric carbon atoms, thus containing multiple optical and stereoisomers. These isomers have different biological activities, i.e., the same pyrethroid, the total ester content is the same, but contains different isomers, insecticidal effect is also very different. Therefore, in the production of pyrethroid pesticides, quality control, efficacy testing and post-application investigation of biometabolic pesticide residues, there is a need to provide an accurate and rapid method for the determination of the total ester and the most biologically active isomer content of the sample.

Materials and Instruments

Apple flesh Apple peel Hawthorn Cowpea
Ethyl acetate Acetone
Ampoule tubes Extraction flasks Capillary sampling tubes Milled triangular flasks

Move

I. Detection methods for pyrethroids 1. Extraction Generally, homogenization extraction method is used. For samples with darker pigmentation, activated charcoal can be added to the homogenization before proceeding. It is also reported to use Soxhlet extractor with ether as the extraction solvent. Zheng Xiaohua microwave-assisted liquid-liquid extraction method for the extraction of vegetables, fruits in a variety of pyrethroid residues, the authors believe that this method compared with their own national standard method, the amount of organic solvents, easy to operate, and greatly improve the speed of analysis. The extraction solvents were mostly acetone or mixed solvents. Purification is usually taken liquid-liquid partition plus column chromatography, column packing with Florisilica and silica gel. However, GPC has also been reported. 2. Detection The detection instrument is usually gas chromatography with electron capture detector, but also reported with HPLC/UV. Gas chromatographic determination of general meters with non-polar to weak column polar column. Pyrethroid pesticides are thermally stable, and the use of capillary columns in the high temperature region (250/280 ℃) is conducive to the separation of less impurity interference, the use of ECD detection with high sensitivity can meet the determination of pyrethroid pesticide residues in food. This is the same as the determination of organochlorines. Therefore, it is expected to determine organochlorine and pyrethroid pesticides at the same time, in general, organochlorine such as BHC, DDT peaks in the front and pyrethroid peaks in the back. Confirmation of the general meters with GC-MS method. Typical analytical methods Take microwave-assisted liquid-liquid microextraction gas chromatography-mass spectrometry (GC-MS) as an example to analyze pyrethroid residues in vegetables and fruits. 1. Pre-treatment steps Microwave extraction: accurately weigh 6 portions of 20.0 g of apple pulp in a 100 mL triangular flask with a milled mouth, add different amounts of pyrethroid standard solution and 1.0 uL of the internal standard solution, the standardized samples were shaken vigorously and put for 10 min, followed by the addition of 15 mL of acetone, in the ice bath under condensation and reflux into the microwave oven, 800 W radiation for 50 s, removed, cooled, and to be liquid-liquid micro-extraction. Weigh 20.0 g each of apple flesh, apple peel, hawthorn and cowpea homogenized pulp in a milled triangular flask, add 1.0 uL of internal standard solution and shake vigorously, and leave for 10 min, followed by the addition of 15 mL of acetone, and the subsequent operation as above. Liquid-liquid microextraction: After microwave radiation, the sample was transferred to a 300 mL liquid-liquid microextraction bottle, diluted to 300 mL with water, 3 g NaCl was added, and 3.5 mL of n-hexane was added with electromagnetic stirring for 2 min, and then the sample was stirred for 15 min and then left to stand, so as to stratify the organic and aqueous phases of the extraction bottle; the organic phase was transferred to an ampoule by a capillary tube and dried by N2 blow-drying at 40 ℃, and 30 uL of acetone was added. The organic phase was transferred to an ampoule tube with a capillary sampling tube, blown dry at 40 ℃, dissolved with 30 uL of ethyl acetate, and 1 uL was taken for GD-MS analysis. 2. GC-MS-NCI detection conditions Interface temperature: 280 ℃, the reaction gas was methane gas; quadrupole temperature: 150 ℃; emission current: 49.4 mA; electron multiplier voltage: 1811 V; ion source temperature 150 ℃. The data acquisition method was selected ion monitoring by time interval. Tefluthrin m/z: 241, 205, 243, 382; bifenthrin m/z: 386, 205, 241, 387; cyfluthrin m/z: 241, 205, 243, 449; permethrin m/z: 207, 209, 354, 390; cyfluthrin, cypermethrin m/z: 207, 171, 173, 209; fluvalinate Cypermethrin m/z: 243, 207, 244, 424; Cypermethrin m/z: 211, 213; Permethrin m/z: 211, 213; Cyfluthrin m/z: 294, 296, 502; Deltamethrin m/z: 297, 217, 294, 299.

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