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16.
1.
4 Residue analysis techniques
Nitroimidazole drug residues have attracted the attention of governments of various countries, and there are many studies on their residue detection methods.
At present, instrumental analysis methods are mainly used
.
Polzer et al.
16.
1.
4.
1 Pre-processing method
Pre-treatment often involves steps such as concentration and drying.
The vapor pressure of this type of medicine is high, and it is easy to be lost by solvent or air flow.
Therefore, the evaporation temperature should not be too high, the blowing speed should not be too fast, and the sample should not be evaporated to dryness.
Slowly blow in nitrogen or air
.
(1) Extraction method
Extraction is to transfer the residual drug in the biological sample through a suitable solvent, and minimize the sample matrix for co-extraction
.
The nitroimidazole drugs and their hydroxyl metabolites in the sample matrix degrade rapidly at room temperature.
1) Liquid liquid extraction (LLE)
Due to the alkaline nature of this type of drug, it is soluble in water under acidic conditions and soluble in organic solvents under alkaline conditions.
After the tissue extract is reconstituted with an acidic aqueous solution, it can be degreased with dichloromethane or n-hexane
.
The extraction of nitroimidazole drugs uses ethyl acetate , acetonitrile, dichloromethane and toluene, etc.
A.
Acetonitrile extraction
Acetonitrile has a good effect on protein precipitation and is miscible with aqueous matrix.
It is one of the commonly used solvents for extracting nitroimidazole drugs from tissues
.
Acetonitrile is used to extract poultry meat samples, and the recovery rate is between 79% and 93%
B.
Ethyl acetate extraction
Ethyl acetate also has a certain compatibility with tissues and is suitable for the extraction of medium-polar drugs.
Many studies have used ethyl acetate to extract nitroimidazole drugs from tissues, but it should be noted that the ethyl acetate extract often contains more fat , Degreasing and purification steps are essential
.
Sun et al.
C.
Dichloromethane extraction
The chemical properties of dichloromethane and ethyl acetate are similar, but the density of dichloromethane is relatively high.
After the extraction is completed, the matrix floats on the top of the extraction solution.
Follow-up operations should minimize secondary pollution
.
When extracting with dichloromethane, adding anhydrous sodium sulfate can absorb the water in the tissue and increase the density of the tissue.
D.
Other solvent extraction
There are also reports of using other solvents for extraction
.
GB/T21318-2007 Determination of 4-Nitroimidazole, IPZ, MNZ, RNZ, MNZ, CMNI, DMZ, Bennimidazole in pork, chicken, beef, pig liver, chicken liver, beef liver, pig kidney, beef kidney and fish For its metabolites MNZOH and HMMNI, the sample is mixed with diatomaceous earth, saturated sodium chloride, methanol-acetone (3+1, v/v), and then homogenized for 3 min.
2) Ultrasonic-assisted extraction (UAE)
UAE uses the strong cavitation effect, mechanical vibration, disturbance effect, high acceleration, emulsification, diffusion, crushing and stirring effects produced by ultrasonic radiation pressure to increase the frequency and speed of the molecular motion of substances and increase the penetration of solvents.
, So as to speed up the target component into the solvent and promote the extraction method
.
UAE is suitable for homogenized samples with loose tissues and structures (such as honey, milk)
Related Links: Metabolism and Toxicology of Nitroimidazole Drugs