Residue Analysis of Oxytetracycline in Milk Sample by Two Different Chromatographic Methods and Determination of Ionization Constant Values

In the present study, two analytical methods for the residue analysis of oxytetracycline in milk sample have been generated. In HPLC method, the analysis was performed on an X Terra RP-18 column at 25 °C with the mobile phase as methanol: water (20 : 80 )(v/v) modified to pH 5. For the second method capillary electrophoresis system was used. The analysis of oxytetracycline in milk sample could be achieved without using organic modifier in a 58 cm length capillary at a working voltage of 12 kV with 20 mM NaH2PO4-H3PO4 (pH 7) by capillary electrophoresis. Tetracycline was used as internal standard in both methods. The results calculated from both methods were compared to each other. The calculated data for drugs was checked with the data predicted by the SPARC on-line pKa estimator.