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The multi-residue detection of pesticides has always been the goal pursued by analytical chemists, and is the research focus and development trend of pesticide residue analysis
In order to provide a legal basis for pesticide residue limits in agricultural products, China has successively formulated relevant pesticide residue standards since the mid-1980s
(1) Gas chromatography and method development
Gas chromatography is currently the most widely used method for the analysis of organophosphorus and organochlorine pesticide residues, and it can also be used for the analysis of other organic substances
Gas chromatograph is a chemical analysis instrument used to separate compounds in complex samples
In gas chromatography, a certain amount (known amount) of gas or liquid analyte is injected into the injection port at one end of the column [usually a micro (automatic) sampler is used, or solid phase microextraction fiber (solid phase microextraction fiber) microextraction fibres)]
Currently, there are more than 20 detectors that can be used in gas chromatographs
1.
(1) Thermal conductivity detector (TCD)
(2) Flame ionization detector (FID)
(3) Flame-photometric detector (FPD)
(4) Electron capture detector (ECD)
(5) Nitrogen-phosphorus detector (NPD)
2.
(1) TCD has strong versatility, stable performance, maximum linear range, high quantitative accuracy, simple operation and maintenance, low cost, easy to popularize, suitable for constant and semi-micro analysis, especially suitable for permanent gas or relatively pure sample analysis
(2) FID is particularly suitable for the macro-to-micro analysis of organic compounds, and is a conventional method for testing the content of active ingredients in pesticide products
(3) FPD is a highly sensitive and selective detector, which is particularly sensitive to phosphorus and sulfur.
(4) ECD is particularly suitable for the analysis of complex multi-component and multi-interfering substances in environmental monitoring and biological samples, but some interfering substances have similar sensitivity (almost no selectivity) to the components to be quantified and quantitatively analyzed, especially in When doing trace analysis, the necessary pre-treatment of the sample should also be carried out, or the column separation should be improved to prevent qualitative errors
.
ECD analysis has high sensitivity to electronegative samples; ECD is sensitive to almost all operating conditions, and its high sensitivity to interfering substances and targets makes the operation of ECD more difficult, and only a small concentration of sensitive substances May cause interference to the analysis
.
(5) NPD has good selectivity and high sensitivity to nitrogen and phosphorus compounds, and is suitable for trace and trace analysis of nitrogen and phosphorus in samples
.
The sensitivity of NPD is related to the molecular structure of the compound.
For example, when detecting nitrogen-containing compounds, it has the highest sensitivity to easily decomposed into cyano groups (-CN).
Other structures, especially nitrates and amides, have little response
.
Related Links: Selection of Pesticide Residue Testing Instruments