Since this January, Isocarbophos, a banned pesticide has been detected in Hainan-grown cowpeas in Wuhan, Hubei Province by the city’s Agricultural Bureau for three times. It is obvious that abuse of this pesticide in planting has resulted in toxic cowpeas. Food Safety Office in Guangzhou City has announced the test result of 5 pcs of Hainan-grown cowpeas on the sale in Jiangnan Fruits and Vegetables Market. The result shows that 2 pcs of cowpeas grown in two cities (Waning and Sanya) of Hainan Province are toxic. Besides Isocarbophos, Carbofuran and Omethoate, these two banned pesticides, have also been detected in Sanya, Hainan-grown Cowpeas. So far, more cities in China have been hit by the scare, such as Wuhan, Shanghai, Zhenzhou, Hefei, Hangzhou, Guangzhou and other 11 cities. We must pay attention to the safety of our agricultural products after this incident.
一、Introduction
1.Introduction of isocarbophos
Chemical name: O-METHYL O-[2-(ISOPROPOXYCARBONYL)PHENYL] PHOSPHORAMIDOTHIOATE
Molecular formula: C11H16NO4PS
Molecular weight: 289.3
Main physical and chemical properties: pure isocarbophos is colorless, scaly crystal, which is soluble in ether, benzene, acetone, acetic ether and insoluble in water, hard to dissolve in petroleum ether; commercial product of isocarbophos is mahogany viscous oily liquid which will precipitate crystals when placed. Content of effective constituent is 85-90%, stable storage in normal temperature. 40% isocarbophos emulsifiable concentrate is yellow or mahogany crystal homogeneous oily liquid.
As a kind of commonly and extensively used insecticide and acaricide, isocarbophos is also called carboxamide phosphorus and is widely used in pest control of agriculture. However, it is stipulated that isocarbophos is banned in vegetables.
2.Introduction of carbofuran:
Chemical name: 2, 3-dihydro-2, 2-dimethyl-7-benzofuranyl methylcarbamate and also known as Carbofuran; molecular formula C12H15NO3, and its relative molecular weight is 221.25. Solubility (g/L,250C): 7 g/l in water, 150 g/l in acetone, 270 g/l in dimethyl phthalate ammonia, 140 g/l in acetonitrile, 90 g/l in cyclohexanone, 40 g/l in benzene. And it can be dissolved in petroleum ether and dimethylbenzene. It is decomposed at 180℃ and stable in acid medium, but unstable in alkali medium. Temperature and alkaline have greater impact on its hydrolysis. Carbofuran is a broad spectrum pesticide and nematicide that kill insects on contact or after ingestion. It is the most toxic pesticide combined with cholinesterase irreversible. The plant can absorb it through the roots, and from here the plant distributes it throughout its organs, mainly leaves. The residual pesticide is usually existing in soil for long time, but easy to disappear in the rice field. It is used against rice, cotton, tobacco, soybean and other crops pests, and as well for seed treatment
3.Introduction of omethoate
Chemical name: Dimethoxon O,O-Dimethyl-S-methylcarbamoylmethyl phosphorothioate
Molecular formula: C5H12NO4PS Molecular weight: 213.2
Main physical and chemical properties: omethoate (AR) is brown oily liquid, readily soluble in water, acetone, chloroform, methanol, ethanol, butanol, hydrocarbons, slightly soluble in ethyl ether, almost insoluble in petroleum ether; stable in neutral, acidic medium, quick hydrolyzed in heat or alkaline medium.
Omethoate is highly-toxic pesticide, strong prevention against aphid, better prevention against plant hopper, leafhopper, scale insect and other pests. Omethoate can maintain its pesticidal property in low temperature, especially suitable to prevent aphid, mites, plant louse, etc. during winter.
二、Solutions
Various testing institutes have begun the test of isocarbophos residues since the “toxic cowpeas”event to ensure the safety of cowpeas. Our company has been devoted to the research in this area and our product LC310 High-frequency Liquid Chromatograph can meet the demand for testing the pesticide residues.
LC310 instrument configurations for isocarbophos and omethoate testing:
P310 high-pressure infusion pump: 1 set
UV310 ultraviolet-visible detector: 1 set
7725i manual introduction valve (20ul loop): 1 set
LC310 chromatographic data processing system: 1 set
Kromasil C18 250*4.6mm, 5um, 100A chromatographic column: 1 piece
DT310 chromatographic column oven: 1 set
Solution tray: 1 set
Isopycnal starter kit: 1 set
LC310 instrument configurations for carbofuran testing:
P310 high-pressure infusion pump: 2 sets
High-pressure static mixer（1.7ml）: 1 set
Fluorescence detector: 1 set
7725i manual introduction valve (20ul loop): 1 set
LC310 chromatographic data processing system: 1 set
Post-column derivatization reactor: 1 set
Kromasil C18 250*4.6mm, 5um, 100A chromatographic column: 1 piece
DT310 chromatographic column oven: 1 set
Solution tray: 1 set
Binary gradient starter kit: 1 set
Laboratory Pre-treatment Devices
Solution filter (with vacuum pump): 1 set
Solution filter membrane (organic, hydro, 0.45μm, diameter 50mm)
Sample filters (organic, hydro, 0.45μm, diameter 13mm)
Glass syringe for filtration various types
Electronic balance (accuracy: 1/100000 or 1/10000)
Ultrasonic cleaner: 1 set
Nitrogen blowing meter: 1 set
Rotary evaporator
Thermostat water bath: 1 set
Pulp refiner: 1 set
Digital thermostatic drying oven: 1 set
Food processor: 1 set
100ml measuring cylinder with stopper: 5
Aluminum foil: 1 coil
Filter paper: 1 box
Other common pre-treatment equipments in the lab
Laboratory reagents:
Acetonitrile: (AR)
Methyl alcohol: (chromatographic pure)
Acetone: (redistilled)
Dichloromethane: (AR)
Sodium chloride: (140℃4h baking)
Anhydrous sodium sulfate: (AR)
Filter aid Celite545
Water: ultrapure water or redistilled water
Sodium hydroxide: (AR)
o-phthalaldehyde(OPA)
OPA dilute solution
Mercaptoethanol
Solid Phase Extraction column, Aminopropyl: 6ml volume, 500mg filler
Pre-treatment of samples:
Isocarbophos: Reference of NY/T 761.10-2004 Method for Organophosphorus Pesticide Residues in Vegetables and Fruits
The sample is extracted via acetonitrile and the extracted solution will be ready for pesticide analysis after purification, concentration and filtration processes.
Carbofuran: Reference of NY/T 761.10-2004 Method for Organophosphorus Pesticide Residues in Vegetables and Fruits
The sample is extracted via acetonitrile and the extracted solution will be ready after solid phase extraction, purification, concentration and filtration processes.
Omethoate: Reference of GB/T5009.20-2003 Determination of Organophosphorous Pesticide Residues in Foods and Vegetables
The sample is extracted in acetone and filtered, and is ready for use after dichloromethane purification and concentration processes.
Preparation of standard solution:
Isocarbophos: Reference of GB24573-2009 Isocarbophos Technical
Weigh 0.1g standard sample (accuracy up to 0.0002g) and put it into 50ml volumetric flask; dilute the standard sample with methyl alcohol to the scale; 5-minute ultrasonic vibration to fully dissolve the sample, and cooled to indoor temperature; suck exactly 5ml with suction pipette from the 50ml volumetric flask, dilute the solution with methyl alcohol to the scale and shake up.
Carbofuran: Reference of NY/T 761.10-2004 Method for Organophosphorus Pesticide Residues in Vegetables and Fruits
Weigh certain amount of carbofuran standard sample, dilute with methanol and make standard stock solution of 1000mg/L and store it in the refrigerator; dilute to standard working solution with needed concentration when used
Omethoate: Reference of HG3306-2000 Omethoate Technical
Weigh certain amount of omethoate standard sample, make constant volume in methanol, shake up and make standard solution with certain concentration.
Requirement for analyst:
Personnel with experience in chemical analytical instruments and related majors or operation of High-frequency Liquid Chromatograph |