Determination Of Metalaxyl Residues In Freshwater Fish

Metalaxyl is a new kind of fish drug usually stead of malachite green to prevent and treat of freshwater fish infected by water mold or other fungus.Although it has been established the MRL in freshwater fish muscle on the announcement No.2505 issued by the Ministry of Agriculture in 2017（trial）,there are no method standards for detecting metalaxyl residues in freshwater fish.In order to regulate the use of metalaxyl in freshwater fish farming in our country and ensure the consumers’health,it’s necessary to monitor this veterinary medicine residue by establishing a detection method for metalaxyl residues in freshwater fish.In the study,5 kinds of freshwater fish were taken as the experimental objects,such as grass carp.After making the optimization to the sample pretreatment,and the conditions of chromatography and mass spectrometry,there are two testing techniques established for metalaxyl residues in the muscle of the freshwater fish,including high performance liquid chromatography（HPLC）and liquid chromatography-mass spectrometry（LC-MS/MS）methods.The follows are about the major research contents and results of this paper:1.The HPLC technique has been built up for testing metalaxyl residues in freshwater fish.The sample was extracted with 0.1%phosphoric acid aqueous solution,and purified by mixed anion exchange solid phase extraction column PAX,lastly it was analyzed by fluorescence detector（FLD）,which was quantified by external standard way.The outcomes showed that the metalaxyl had good linear relevance between 0.05μg/m L and 5μg/m L for the standard solutions carve with the correlation coefficients（R²）0.9999.The limits of detection of metalaxyl were 0.006 mg/kg,while the limits of quantification were0.02 mg/kg.When the blank samples,including grass carp,tilapia,carp and so on,were respectively added with the consistence of 0.02 mg/kg,0.05 mg/kg,0.10 mg/kg standard solutions,the average recoveries were between 79.7%and 92.6%,and the relative standard deviations were 1.1%～8.0%.There were many advantages in the method,such as simple pretreatment operation,less impurity interference as well as high sensitivity and recovery and so on.2.The LC-MS/MS technique has been set up for detecting metalaxyl residues in freshwater fish.The sample was drew with acetonitrile,and cleaned-up by PSA,C₁₈,and its extracts were ionized by ESI⁺under the mode of MRM,which was quantified by external standard method.It showed that metalaxyl had good linear relationship from 0.5 ng/m L to 20 ng/m L for the standard solutions carve with the correlation coefficients（R²）0.9990.The limits of detection and limits of quantification were 0.0015 mg/kg and 0.005 mg/kg.When the blank samples,such as grass carp,tilapia,carp,silver carp,crucian carp and so on,were respectively added with the concentration of 0.010 mg/kg,0.025 mg/kg,0.050 mg/kg standard solution,the mean rate of recoveries were between 82.5%and 97.7%,and the RSD were 1.7%～8.2%.The method built-up in this paper used the mass spectrometer to test the metalaxyl residues,which can prevent mistaking the samples,while the quantitative limit was 4 times lower than that of HPLC.What’s more,LC-MS/MS had little inference from other impurities and more accurate ability of quantitation.3.Do some detection to the freshwater fish sample about the metalaxyl residuesIn total 60 samples,12 types of freshwater fish,including grass carp and so on,were detected by HPLC and LC-MS/MS established in this paper.There were 2 samples detected with metalaxyl residues,they were carp and crucian carp.The results detected by HPLC were 0.0374 mg/kg and 0.0423 mg/kg,when they got the outcomes 0.0370 mg/kg and 0.0415 mg/kg respectively by LC-MS/MS.The results of metalaxyl in 12 types of freshwater fish samples did not exceed the maximum residue of 0.05 mg/kg specified on the announcement No.2505 from the Ministry of Agriculture.Through the detection of actual samples,it was found that the results of the two detection methods established in this paper were within the allowable error range.Therefore,the two methods established in this paper can be used to detect metalaxyl residues in freshwater fish.