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among the pesticides banned by the state, chlordimeform and acephate have been detected by high frequency. because of the high illegal cost of banned pesticides and the control of raw drugs, the probability of banned pesticides being used as recessive additives is relatively small. in order to occupy the pesticide market by increasing the efficacy of pesticides, illegal manufacturers make a big fuss on the implicit addition. a variety of implicit pesticides are added at the same time, which greatly increases the difficulty of law enforcement sampling.
therefore, according to the national pesticide law enforcement cases and the station's many years of testing experience, 25 kinds of high-frequency illegally added pesticides are summarized.
fenitrothion, triazophos, fenitrophos, pyridaben, cypermethrin, fenpropathrin, buthikebaiwei, zhongdingwei, acephate, fipronil, isocarbophos, high-efficiency cypermethrin, methomyl, chlorpyrifos, high-efficiency cypermethrin, pymetrozine, imidacloprid, acetamiprid, carbofuran, quinazone, phoxim, flusuurea, bromofenitrile, avermectin bacteriocin.
according to the physical and chemical properties, instrument adaptability, similarities and differences of detection standards, and interference of components with similar peak time of the above 25 banned pesticides, they are divided into two parts of high performance liquid chromatography (10 kinds) and gas chromatography-mass spectrometry (15 kinds) for repeated experiments, and the test conditions obtained are for readers to refer to. the biggest characteristic of this method is to unify gc-ms and hplc.
experimental part
liquid chromatography experiment part
(1) instrument
agilingt 1260 high performance liquid chromatograph, ultrasonic cleaner.
(2) reagents
10 pesticide standards, such as pymetrozine, imidacloprid, acetamiprid, carbofuran, chlorobenzamide, quinolinone, phoxim, fluorosuzuki, bromofenitrile, avermectin (content ≥ 99.0%); pure methanol (solvent) chromatography; ultra pure water.
(3) selection of chromatographic conditions
methanol water system: gradient; chromatographic column: 250mm stainless steel column; mobile phase elution gradient. flow rate: 1.0ml/min; column temperature: 25 ℃; detection wavelength: 254 nm; injection volume: 10 μ l. the chromatogram of mixed standard samples and retention time of 10 kinds of standard samples are separately located according to the elution conditions for each standard sample, and no one by one list is attached.
（4） experimental steps
standard solution: prepare about 0.0500 g / 50 ml methanol solution of the above 10 pesticides.
put 2 ml of each of the 10 standard solutions into a 50 ml volumetric flask and prepare them into a mixed standard. finally, the chromatogram of the mixed standard is obtained according to the elution gradient, and the repeatability of the chromatogram is verified by multiple injections.
the retention time of 10 pesticides was 3.35 min for pymetrozine, 4.12 min for imidacloprid, 4.97 min for acetamiprid, 9.87 min for carbofuran, 16.75 min for chlorobenzamide, 17.59 min for quinolinone, 29.76 min for phoxim, 32.83 min for fluroxylurea, 33.61 min for bromofenitrile and 44.06 min for avermectin.
（5） conclusion
the elution gradient of a single standard sample was analyzed qualitatively and the retention time was determined one by one.
in the detection of pesticide recessive components by liquid chromatography, it is necessary to weigh the samples according to the determination conditions of prohibition limit, then compare the peaks of each component of the samples with the peaks of the mixed standard samples to determine the addition of suspected recessive components with the same and similar peak time, and finally carry out quantitative analysis of the suspected components.
gc-ms experiment
1) instruments and conditions
agilent 7890b-5977a gc-ms column: 30 m × 0.25 mm (i.d.) dv-17ms quartz capillary column with a membrane thickness of 0.25 μ m (or equivalent); microinjector: 10 μ l; temperature: 100 ℃ for 2 min, gradient, because methomyl peak time is earlier, set solvent delay for 2 min, gc operation gradient
gas flow (ml / min): carrier gas (he) 1.5; split ratio: 10:1; injection volume: 10 μ l; ionization energy: 70 ev; ion source temperature: 230 ℃; four-stage rod temperature: 150 ℃; auxiliary channel temperature: 280 ℃; scanning mode: full scanning; retention time.
(2) reagents
15 agricultural drug standards, such as fenitrothion, triazophos, fenitrophos, pyridaben, cypermethrin, fenpropathrin, buthikebudweil, zhongdingwei, acephate, fipronil, isocarbophos, high-efficiency cypermethrin, methomyl, chlorpyrifos, and high-efficiency cypermethrin (content ≥ 99%); avermectin emulsifiable oil samples; chromatography level acetone.
(3) experimental steps
weigh about 0.05 g of each of the 15 pesticide standards into the same reagent bottle, add 50 ml of acetone, fully dissolve them into the mixed standard sample, take 1.5 ml of the solution with a burette to mark the sample bottle i; weigh 0.25 g of avermectin 1 × sample into the reagent bottle, add 50 ml of acetone, fully dissolve them, take 1.5 ml of the solution with a burette to mark the sample bottle ii. peak output of sample bottle i and ii
the peak time of standard samples of 15 pesticides: methomyl 2.27 min; acephate 5.9 min; zhongbutwei 7.56 min; fenitrophos 8.42 min; buthicarbaryl 9.24 min; fenitrothion 12.61 min; chlorpyrifos 13.19 min; isocarbophos 13.47 min; fipronil 14.56 min; triazophos 17.79 min; fluthrin 20.91 min; fenpropathrin 21.2 min; flufenpropathrin 22.61 min; pyridaben 23.53 min min; cypermethrin 24.95 min.
the peak time of abamectin ec was 13.35 min for chlorpyrifos, 21.11 min for acetamiprid and 22.66 min for cypermethrin.
(4) conclusion
after repeated condition exploration and gradient adjustment, the mass spectrum was obtained. the peak time of methomyl was earlier, and the delay time of solvent was changed from the initial 3.00min to the final 2.00min; the response value of acephate was lower, and the standard dose could be increased appropriately in actual operation, and the peak time was checked separately to find out whether the component was contained.
comparing the mass spectrum of abamectin pesticide samples, it was found that the samples contained three banned pesticides, chlorpyrifos, acetamiprid and cypermethrin, which was a typical case of illegal addition.
general theory
in the investigation of these 25 prohibited and restricted pesticides, the difference from the existing literature is that the first 10 pesticides that can not be detected by gc-ms are put in the liquid chromatography for detection, increasing the reliability of the overall investigation. based on these 10 methods, methanol with low toxicity and low cost is used instead of acetonitrile in the selection of mobile phase; the absorption wavelength is determined to be 254 nm through repeated trials; in view of the acid conditions and buffer phosphates may lead to the decomposition or peak abnormality of some samples, no acid and salt are added to the mobile phase temporarily in this experiment. 15 pesticides detected by gc-ms are used as a whole standard sample mass spectrum for accurate comparison of later samples. once suspicious components are found, they are analyzed quantitatively by liquid chromatography. gc-hplc was used.
pesticide, as a special commodity to control pests and pests of crops, plays an important role in increasing agricultural output and farmers' income. if the quality of pesticide is unqualified or used improperly, it will lead to pesticide residues in agricultural products exceeding the standard, human and animal poisoning, and ecological environment pollution. an ordinary avermectin emulsifiable concentrate was added with three banned and restricted pesticides. therefore, this comprehensive analysis method is developed to reduce the cost of investigation and achieve the popularization effect of illegal addition of pesticides, so as to promote the healthy development of the entire pesticide industry.