HPLC Determination Of Roxarsone And Its Elimination In Feces Of Swine

A high performance liquid chromatography (HPLC) method was developed for determination of roxarsone levels in feces of swine. The feces of swine were extracted by dipotassium hydrogen phosphate,and cleaned up by Waters Oasis~R MAX SPE column.HPLC mobile phase consisted of potassium dihydrogen phosphate(0.05 mol/L),methanol and acetic acid. The limit of detection and limit of quantitation of roxarsone in feces of swine was 0.05mg/kg and 0.1mg/kg,respectively. The standard curves were observed to be linear from 0.05～2.0mg/kg for roxarsone in pig feces.The mean recoveries of roxarsone ranged from 82.09%～84.03%. Coefficients of variation ranged from 2.92%～5.45%,are preferably good for residue analysis.Twenty-four healthy changmei crossbreed pigs were randomly divided into 4 groups of 6 pigs each.The animals were fed with feed containing roxarsone (25,50,100mg/kg).Then, the feces were collected at different time from 0 to 120h. The concentrations in feces were determined by HPLC.The results obtained from experiment were as follows:Pigs began to excreted roxarsone at twenty-four hours after feeding with feed containg roxarsone. In the group with the addition of 25mg/kg roxarsone, the amount of roxarsone that was excreted by swines reached the peak at 36h after feeding, with a peak concentrarion of 12.31mg/kg; while in the groups with the addition of 50-and 100- mg/kg roxarsone, the amount of roxarsone reached the peak at 48h,with the peak concentration of 22.52 and 34.78mg/kg.Then, the amount of roxarsone in the feces reduced gradually,and roxarsone was undetectable in swine feces within 72h,108h and 132h,respectively.1ml 250mg/L standard solution of roxarsone was spiked in the fresh swine feces without roxarsone after sterilization, yeilding the concentration of roxarsone 50mg/kg in each sample.The sample was divided into two groups,one incubated at 25℃in the incubator without light while another at 25℃in the light.The sample was collected at indicated times, and the concentration of roxarsone was determined by HPLC.Roxarsone in the swine feces was stable and not subjected to degradation,either without light or in the light.Under the initial concentration of 50 mg/kg, roxarsone degraded only by 11.63% and 21.68%, respectively,after seven days of degradation. 150 samples of swine feces were randomly collected from fifteen swine farms in Shandong and Jiangsu province,and the investigation was conducted to determine the concentration of roxarsone in pig feces.The minimum concentration of roxarsone in the feced was 12.36mg/kg, wheras the maximum was 31.57mg/kg.The average concentration of roxarsone in the feces from 15 farms was 23.13mg/kg.