The Development Of Analytical Method For Screening Typical Chemical Contaminants In Bovine Milk

Milk is an important part of people's healthy diet,and its safety has received great attention.Various kinds of chemical contaminants such as veterinary drugs,pesticides and mycotoxins may produce residues in milk because of direct uses or indirectly pollution.The technical methods currently reported are mainly used to detect the single category of contaminant,and are difficult to screen and detect different kinds of contaminants simultaneously.This is unable to meet the supervision requirements for food safety under the new situation.According to this,the optimization of sample preparation was achieved by exploring the intrinsic change behaviour of sample matrix according to lipidomics study,and this could be the fundamental theory of establishing the method of screening and quantitative determination of 209 chemical contaminants in milk.Finally the method was validated and applied in real samples.The related results were as follows:First,lipidomics was used to investigate the effects of different extraction and purification conditions on the lipid content of different classes in milk.The addition of formic acid,acetic acid or EDTA buffer salts in the extract would lead to changes in various types of lipids.With the increase of acid and buffer,PC lipids present an irregular change,PE,PS and PI lipids show a decreasing trend.After salting-out treatment,PC lipids still show irregular changes,the other three types of lipids show an increasing trend,which is opposite to the unsalted.With the increase of acid and buffer,the effects of salting-out become obvious due to the obvious increase in total lipids content.Different sorbents have different adsorptive capacity for lipids in the extract.C18 presents a stronger adsorptive capacity for PC and PS lipids,PSA is second to C18,but ZrO₂ is for PE and PI lipids.When acid or buffer is added,the adsorptive capacity of PSA and C18 does not change significantly.But ZrO₂ and EMR are greatly affected by the increase of acid,and ZrO₂ was also greatly affected by the EDTA buffer.Different lipid content in extracts have different matrix effects on chemical contaminants,the total lipid content shows an increasing trend with the increase of acetic acid after salting out,and all contaminants do not show obvious changes,but veterinary drugs are difference with pesticides and mycotoxins.When the volume of EDTA buffer is 7.5 mL,the matrix inhibition was observed.But the matrix enhancement effect was obvious at 10 mL,and the effect on each compound was quite different.Secondly,based on the results of lipidomics and investigation of matrix effects,The QuEChERS method was optimized for sample preparation,and 2%acid in acetonitrile was selected as the optimal extraction solution.By comparing four sorbents including PSA,C18,EMR and ZrO₂,C18 was selected to be the cleanup sorbent.Then,a mass spectrometry database of contaminants was constructed by UHPLC-QTRAP-MS.A method for simultaneous screening and quantitative confirmation of 209chemicals,including 138 veterinary drugs,55 pesticides and 16 mycotoxins in bovine milk was established and validated.The results showed that the recoveries ranged from 51.20%to 129.76%and the RSDs was 0.82%-19.76%.The limit of quantification?LOQ?of the method is 0.05?g/kg-5?g/kg,which meet the maximum residue limit requirements of related contaminants in bovine milk set by China or European Union,and the qualitative confirmation can be achieved at the same time of accurate quantitation.Finally,the established method was used to screen and qualitatively analyze real bovine milk and feed samples.The positive samples were found with lower concentrations of imidacloprid,acetamiprid,fipronil sulfone,cloxacillin,sulfamethazine and aflatoxin M1 in bovine milk samples.Compared with the literature in recent years,51 contaminants and relevant metabolites in bovine milk have been reported,of which 80.4%are veterinary drugs.Penicillin G and chlorzocillin in beta-lactams,enrofloxacin and ciprofloxacin in quinolones,and sulfamethazine in sulfonamides are relatively high-frequency drugs in different countries,and should be given priority attention.