Determination of organophosphorus pesticide residues

Summary

In order to study the nature and role of food contaminating factors, some modern techniques are used to detect their levels in food, to determine the safe dose of toxicants using knowledge of toxicology, to evaluate the safety of food, and to elucidate whether a certain food is safe for consumption. Source: Food Safety Testing Technology (Chemical Industry Press)

Operation method

Techniques for the determination of organophosphorus pesticide residues

Principle

Organophosphorus pesticides (organophosphorus pesticides, referred to as OPPs) are organic compounds that contain C-P bonds or C-O-P, C-S-P, C-N-P bonds. -P bond of organic compounds, currently in common use there are four major categories: 1. phosphate esters of phosphoric acid in the three hydrogen atoms replaced by an organic group to generate compounds called phosphate esters. 2. phosphorothioate class of phosphoric acid molecules in the replacement of oxygen atoms by sulfur atoms to generate compounds for the phosphorothioate, phosphorothioate in the replacement of hydrogen atoms by an organic group, which is to become the phosphorothioate esters. 3. phosphonate class and phosphorothioate class of phosphoric acid, phosphoric acid and phosphoric acid. Phosphoric acid esters and phosphorothioate esters in a hydroxyl group is replaced by an organic group! That is, in the molecule to form a P-C bond is called "phosphonic acid", phosphonic acid in the hydrogen atom of the hydroxyl group is replaced by an organic group that is phosphonate, or phosphonate in the oxygen atom is replaced by a sulfur atom, that is, phosphonothioate. 4. Phosphoramidites and thiophosphoramidites phosphoric acid molecule of the hydroxyl group is replaced by an amino group to produce phosphoramidite; or the remaining oxygen atom in the phosphoramidite molecule is replaced by a sulfur atom, which becomes phosphoramidothioate.

Materials and Instruments

Grain Oilseed
Acetone Dichloromethane Sodium chloride aqueous
Stoppered conical flasks Filter flasks Gel columns Dispensing funnels Fraction collectors

Move

1. Extraction Method 1 (Homogenized extraction) Weigh about 20 g (0.1 g) of the sample into a 250 mL stoppered conical flask, add 20 mL of water, shake and leave for 1 h. Then add 100 mL of acetone and homogenize the extract for 3 min at high speed, and then filter the extract into a 250 mL pear shaped flask. The residue was extracted again with 50 mL of acetone, and the filtrate was combined and concentrated to about 20 mL in a 40 ℃ water bath with rotation for purification. Method 2 (ASE rapid solvent extraction) Weigh about 20 g (accurate to 0.1 g) of the sample in the sample cell, sealed, according to the specified conditions [ASE extraction conditions extraction solvent: dichloromethane; pressure: 1500 psi (l psi = 6894.76 Pa); temperature: 50 ℃; extraction volume: 60 mL; static time: 5 min] for the extraction and purification. 2. 2. Liquid-liquid partition purification The concentrated extract was transferred to a 250 mL dispensing funnel, 150 mL of aqueous sodium chloride and 50 mL of dichloromethane were added (no need to add dichloromethane for ASE extraction), shaking for 3 min, static layering, and the dichloromethane phase was collected. The aqueous phase was then extracted twice with 2×50 mL dichloromethane, and the dichloromethane phase was combined. It was dehydrated by an anhydrous sodium sulfate column, collected in a 250 mL pear-shaped vial, concentrated to near dryness by spinning in a water bath at 40 C. 5 mL of cyclohexane-ethyl acetate (1 + 1) was added to dissolve the residue and filtered through a 0.45 um filter membrane. 5 mL of the solution to be purified was purified by GPC. 3. Purification by gel chromatography Combine the collected liquids from the fraction collector in a 500 mL pear shaped bottle, rotate and concentrate in a water bath at 40 ℃ until nearly dry, add 2 mL of n-hexane to dissolve the residue, and leave it to be purified by SEP. Gel chromatography (GPC) conditions: clean-up column: 700 mm×25 mm, Bio BeadsS-X3, or equivalent; mobile phase: cyclohexane-ethyl acetate (1 + 1); flow rate: 5.0 mL/min; sample quantification loop: 5.0 mL; pre-rinse volume: 50 mL; elution volume: 200 mL; collection volume: 90 ~ 190 mL. 4. Solid phase extraction cleanup
The column was pre-drenched with 6 mL of hexane, the sample solution was poured into the column, washed with 2 mL of hexane, and then eluted with 20 mL of hexane-ethyl acetate (2 + 3). All the eluate was collected in a 50 mL pear-shaped bottle, concentrated to dryness by spinning in a water bath at 40 ℃, dissolved with n-hexane and concentrated to 2.0 mL for determination and confirmation by gas chromatography-mass spectrometry (GC-MS). 5. Determination Ionization mode: EI; Ionization energy: 70 eV; Measurement mode: selected ion monitoring mode; Solvent delay: 5 mD;

Common Problems

A variety of organophosphorus pesticide residue analysis, the current common use of gas chromatography flame photometric detector method (GC- FPD), the method of high sensitivity, good separation effect, quantitative accuracy. After many years of practical use, it has been proved to be a classical and applicable analytical method. However, in gas chromatography analysis, the phenomenon of interferents and substances to be measured having the same retention time in the same column often occurs, especially for unknown samples of pollutants is more likely to cause false positives. Therefore, gas chromatography/mass spectrometry selected ion method (GC-MSD) for corroboration is an effective means to solve this problem.Stan reported PICI and EI mass spectra of 23 organophosphorus compounds and confirmed their presence in foodstuffs on the ng/g scale.The molecular ion peaks of the compounds in the EI mode were weak or absent. In the PICI mode, all compounds had strong M+1 ion peaks compared to EI. Recently, Richardson and Seiber used EI mass spectrometry to confirm the presence of organophosphorus metabolites (dimethylphosphate, diethylphosphate, dimethylphosphorothioate, dimethyldithiophosphate, diethyldithiophosphate, diethyldithiophosphate, and diethyldithiophosphate) in the livers and kidneys of pigeons exposed to diaminon and parathion. These compounds were analyzed by GC-MS as butyl derivatives.

At present, there have been many reports on the application of gas chromatography analysis of organophosphorus pesticides at home and abroad, especially on the fruits (vegetables and other samples of organophosphorus pesticide residues in the gas chromatography more research), but the literature on the detection of gas chromatography of fatty foods is less, only the American Association of Public Analytical Chemists to develop the official method of analysis and the Ministry of Health of the country to develop the national standard method for determining the organophosphorus pesticides in meat (fish). Only the official analytical method formulated by the American Association of Public Analytical Chemists and the national standard method formulated by the Ministry of Health in China used gas chromatography in the determination of organophosphorus pesticides in meat (fish).

For organophosphorus pesticides with high boiling point or thermally unstable and easy to crack and deteriorate which cannot be detected by gas chromatography, HPLC method can be used.Nearly half of the organophosphorus pesticides in AOAC have established HPLC method, and there are more research reports. For example, Paul Zavitsanos studied the conditions for the determination of organophosphorus by LC/MS for 17 organophosphorus pesticides.

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