Multi-residue assay of 446 pesticides in fruits and vegetables
Multi-residue assay of 446 pesticides in fruits and vegetables
China has made great progress in recent years in the series determination of many kinds of pesticide residues. Source: Food Safety Monitoring Technology (Chemical Industry Press)
Operation method
Gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry
Materials and Instruments
Vegetables Fruits Move 1. Extraction For more product details, please visit Aladdin Scientific website.
Sodium Chloride Acetonitrile Sodium Sulfate Anhydrous Toluene
Envi-18 Column Envi-Carb Activated Carbon Column Sep-Pak Aminopropyl Solid Phase Extraction Column Gas Chromatography-Mass Spectrometer Liquid Chromatography-Tandem Mass Spectrometer
Weigh 20 g of sample (accurate to 0.01 g) in an 80 mL centrifuge tube, add 40 mL of acetonitrile, and extract by homogenization with a high-speed tissue masher at 15000 r/min for 1 min; add 5 g of NaCl, and then homogenize for another 1 min; put the tube into a centrifuge, and centrifuge it at 3000 r/min for 5 min; take 20 mL of supernatant (equivalent to the amount of 10 g of sample), and leave it to be purified. Purification.
2. Purification
(1) The pesticides in groups A, B, C and D were purified.
Put the Envi-18 column into the stationary rack, pre-wash the column with 10 mL acetonitrile before adding samples, connect the chicken-centered vial underneath, transfer the above 20 mL of extraction solution and elute with 15 mL acetonitrile, and then rotate and concentrate the eluate in a water bath at 40 ℃ to about 1 mL, and then set aside.
(2) For Group E pesticides
Concentrate the above 20 mL of extract to about 1 mL by rotating in a 40 ℃ water bath, and set aside.
About 2 cm high was added to an Envi-Carb column anhydrous sodium sulfate , which was attached to the top of a Sep-Pak aminopropyl column, and the tandem column was placed in a stationary rack underneath a chicken-centered vial. Pre-wash the column with 4 mL of acetonitrile + toluene (3 + 1) before adding the sample. When the liquid level reaches the top of the sodium sulfate, quickly transfer the sample concentrate (①) or (②) to the clean-up column, and then wash the vial of the sample three times at a time with 2 mL of acetonitrile + toluene (3 + 1), and transfer the wash solution into the column. A 50 mL reservoir was added to the tandem column, and the pesticides were eluted with 25 mL of acetonitrile + toluene (3 + 1), combined in a chicken-centered vial, and concentrated to about 0.5 mL by rotary evaporation in a 40 ℃ water bath. For pesticides of Groups A, B, C, and D, 5 mL of n-hexane was added to the column each time by rotary evaporation in a 40 ℃ water bath for solvent exchange two times, and the final volume of the sample liquid was made to be about 1 mL, and 40uL of the internal standard solution was added, and mixed. Mix well and use for GC-MS determination. For pesticides in group E, put the concentrate on a nitrogen blow-dryer and blow-dry it, and quickly volume 1 mL with acetonitrile + water (3 + 2), mix well and use for liquid chromatography-tandem mass spectrometry determination.
3. Determination
(1) Gas chromatography-mass spectrometry
Column: DB-1701 (3O m×0.25 mm×0.25um) quartz capillary column;
Column temperature program: 40 ℃ for 1 min, then 30 ℃/min to 130 ℃, then 5 ℃/min to 250 ℃, then 10 ℃/min to 300 ℃ for 5 min;
Carrier gas: helium, purity ≥99.999%, flow rate of 1.2 mL/min;
Inlet temperature: 290 ℃;
Inlet volume: 10 L;
Sampling mode: no shunt injection, open the shunt valve and spacer purge valve after 1.5 min;
Electron bombardment source: 70 eV;
Ion source temperature: 230 ℃;
GC-MS interface temperature: 280 ℃.
Selected ion monitoring: one quantitative ion and 2/3 qualitative ions were selected for each compound respectively. All the ions to be detected in each group were detected according to the order of peaks; separately in time slots.
The method is based on the quantitative determination of single ions by internal standard method. The internal standard was heptachlor epoxide. In order to reduce the influence of matrix, the standard for quantification should be a matrix mixed standard working solution. The concentration of the standard solution should be similar to that of the compound to be tested.
(2) Liquid chromatography-tandem mass spectrometry
Column: AtlantisTMdC18, 3um, 150 mm×2.1 mm.
Column temperature: 40 ℃.
Injection volume: 2O0 L
Scanning mode: positive ion sweep
Detection method: multi-reaction monitoring
Electrospray voltage: 55OO V
Atomizing gas pressure: 0.076 MPa
Air curtain gas pressure: 0.083 MPa
Auxiliary gas flow rate: 6 L/min
Ion source temperature: 350 ℃