Study On The Residue And Withdrawal Of Chlortetracycline In The Egg And Tissues Of Laying Hens

A high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS)method for the determination of chlortetracycline(CTC)and 4-epi-chlortetracycline(ECTC)was established.to investigate the deposition and withdraw of chlortetracycline in eggs and hen tissues.Exp.l Screening and Optimization for the Separation and determination methods of Chlortetracycline and Chamamycin Residue in Eggs and Layer tissuesThe effect between HPLC and HPLC-MS/MS on the determination of CTC residues in the samples was compared.The test limit of HPLC method is too high,not suitable for the determination of low concentrations of CTC residue.HPLC-MS/MS method fits the requirement of CTC determination,however,when the external standard method is used,the recovery rate is unstable.Finally,the internal standard mehod was used as the quantitative method,while the demethylchromycin was used as the internal standard.O.lmol/L Na2EDTA-Mcllvaine buffer was used as the extraction solvent,the samples were purified by Oasis HLB SPE column,the purification method had achieved good effects,and high recovery rate.The liquid chromatographic conditions were selected by screening the liquid chromatography conditions,the mobile phase was methanol and 0.1%formic acid,a good separation effect was achieved by gradient elution.When the concentration of CTC and ECTC was 0.5～150μg/kg,the peak area was linear.The limit of detection was 0.5μg/kg and the limit of quantification was 1.0μg/kg.Exp.2 Study on residue and withdraw of chlortetracycline in eggs and layer tissuesTo investigate the deposition and elimination of CTC in eggs and layer tissues,a single factor random test was designed.A total of 120 laying hens(62wk aged)were divided into four treatment groups according to body weight and egg laying rate,each group contains 6 replicates,and each replicate contains 5 hens.The test period is 26 days,at 1-12 days the drug capsules,which contains 4 different CTC concentration level of Omg(control),6mg,12mg,24mg respectively,were fed to hens of different group on 8:00 daily.At 13-26 days,fed no drug capsules(withdraw period).Eggs were collected on 12:00,16:00 and 20:00 at the first day of the trial,and on 16:00 from the next day to the last.Layer tissues were collected at the first,6th,11th,15th day of withdraw period for CTC and ECTC determination.The result shows that CTC and ECTC residues were detected in eggs collected after 8h of oral administration of different concentrations of CTC,and the residues deposited with the passage of time.The residues increased fast at the first 1-4 days,then the amplitude decreased.CTC and ECTC residues in eggs and tissues collected from hens which took higher conentrations of CTC were higher than low concentration treatment group.Residues in egg yolk were higher than in egg white,and residues in kidney were the highest,followed by which in liver,and residues in muscle,muscular stomach,intestine,and uterine tube were closer.Residues in eggs and hen tissues decreased after withdraw of CTC intake,the elimination of residues in higher concentration treatment group was longer,and egg yolk were longer than egg white.For tissues the elimination of residues in kidney was longest,followed by liver.The results of this study showed that after hens were fed by CTC,it would deposit in egg and hen tissues,the residues were positively correlated with the residual time and dosage.