a trace analysis of oxytetracycline and tetracycline residues in pasteurized milk supplied in tehran: a one-year study (april 2011-march 2012)

background: tetracyclines (tcs) are broad-spectrumantibiotics that are widely used in veterinary medicine. thepresence of tcs residues in milk is a public health concern allover the world. objectives:this study aimed to determine tcsresiduals in pasteurized milk marketed by some dairy companiesin tehran from april 2011 to march 2012. methods: 432pasteurized milk samples were purchased from supermarketssupplying the milk products of 12 major dairy companies intehran (3 samples from each company every month), and theywere stored at -20 0c until analysis. oxytetracycline (otc) andtetracycline (tc) residues in each sample were extracted by aliquid - liquid phase procedure and quantitated using a highperformance liquid chromatographic (hplc) method. chromatographicconditions included a mobile phase as oxalic acidbuffer- acetonitril (80: 20) with a flow rate of 1ml/min and uvdetectionat 355 nm. results: tcs residuals in most milksamples were lower than 100 ppb, maximum residue level(mrl); however, in seven samples (1.62%) the total residues ofotc and tc were more than mrl. in the latter milk samples, themedian total tcs residue was 625 ppb, ranging between 274 and1270 ppb. conclusions: because of the presence of tcresidues above the mrl level in a limited number of milksamples, it is concluded that more studies and supervision ofhealth authorities are needed in this field.