| Milk is an essential part of people's daily life.However,the milk and its products were contaminated so badly that the problems of quality and safety often occurred.Residues of veterinary drugs are mainly come from the process of prevention and treatment of cows.There are much hazards that can be caused by excessive use of veterinary drugs in milk,such as fermentation of milk,allergies and dysbacteriosis.It can even cause teratogenic,carcinogenic and sudden mutations.What is worse,it affects the development of animal husbandry negatively.In order to regulate food safety,European Union,Japan,Canada,China and other countries have established the maximum residue limits(MRLs)of some veterinary drugs in milk.A method was established to determine 25 veterinary drugs(8 ?-lactams,5 quinolones,5 ?-receptor agonists,3 chloram phenicols,3 glucocorticoids and furazolidone)in milk by liquid chromatography coupled to tandem mass spectrometry.1.A method for simultaneous determination of 25 veterinary drugs in milk samples by LC-MS/MS was established.The extraction method is based on extraction with acetonitrile and defatting by n-hexane.Degreasing steps were repeated one time.The solution was evap-orated on35?.Residue was dissolved with acetonitrile:water(V:V=5:95)solution,vortexed and centrifuged by a high-speed centrifuge,through a 0.22 ?m microfiltration membrane.The target compounds were separated on a Waters X-Bridge C18(5.0 um,2.1 mm×100 mm)column,using acetonitrile(0.1% formic acid)-water as mobile phase with gradient elution.And then detected by HPLC-MS/MS under positive and negative ion mode with multiple reaction ion monitoring.In order to get a high sensitivity at a concentration of the maximum residue limit(MRLs)for 25 analytes,method validation was based on the European Commission Decision 2002/657/EC,including specificity,decision limit(CC?),detection capability(CC?),recovery,precision,accuracy,linearity and stability of the projects.The results showed the linear range of enrofloxacin,ofloxacin,chloramphenicol,hydrocortisone,dexamethasone,florfenicol was 0.1~10 ng/mL,salbutamol,terbutaline,norfloxacin,ciprofloxacin,sparfloxacin was 0.2~50 ng/mL,ractopamine,clorprenaline,prednisone,thiamphenicol,ampicillin,oxacillin,cloxacillin was 0.5~50 ng/mL,clenbuterol,piperacillin,cefoperazone was 1~100ng/mL,penicillin G and cefazolin was 4~256 ng/m L,furazolidone was 4~128 ng/mL,cephalexin was 12~384 ng/m L.For compounds which have MRLs in bovine milk,the CC? values fall into a range from 0.32~113.68 ?g/kg and CC? of 0.36~125.75?g/kg.For compounds which have no MRLs in bovine milk,the CC? values fall into a range from 0.01~2.80 ?g/kg and CC? of 0.01~3.09 ?g/kg.Absolute recovery rates of the 25 analytes was 65.9%~123.5% and relative standard deviation(RSD)was below 7.76%.The RSD of accuracy and inter-,intra-day precision were85.08%~114.6% and 0.89%~11.03%,respectively.The spiked samples were stable at-20? for 3 days and 7 days.Method validation showed that the method was accurate and reliable.2.The analysis method was ued to detect milk samples from the market.According to the milk pretreatment method,20 milk samples of four different brands,purchased in a supermarket,were isolated and detected by LC-MS/MS.Three positive samples were found.Clorprenaline was detected in two samples respectively,which were not approved. |
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