Four antibiotics, oxytetracycline, tetracycline, doxycycline, and chlortetracycline were separated and quantified in medicated feed. Tetracyclines from feed samples were extracted with 0.01 M citric buffer and acetonitrile (pH 3.0) and further purified with 0.45 µm syringe filters. The purified extract was separated on commercial RP-C18 column and analyzing using liquid chromatograph (LC) with two different detectors: diode array detector (DAD) and mass spectrometry (MS). These methods provided average recoveries from 72.2 to 101.8% for high pressure liquid chromatography (HPLC) with diode array detection and from 45.6 to 87.0% for liquid chromatography with mass spectrometry. The limit of detection in medicated feed ranged from 4.2 to 10.7 mg kg⁻¹ for HPLC–DAD and 5.6 to 10.8 mg kg⁻¹ for LC–MS. Our experiment showed that using the same extraction mixture we do not obtain the same recovery values for the analyzed compounds using two different detection techniques such as DAD and MS.

在加药饲料中分离并定量了土霉素、四环素、强力霉素和金霉素四种抗生素。使用 0.01 M 柠檬酸缓冲液和乙腈 (pH 3.0) 提取饲料样品中的四环素，并使用 0.45 µm 注射器过滤器进一步纯化。纯化的提取物在商业 RP-C18 柱上分离，并使用液相色谱仪 (LC) 进行分析，使用两种不同的检测器：二极管阵列检测器 (DAD) 和质谱法 (MS)。这些方法为采用二极管阵列检测的高压液相色谱 (HPLC) 提供了 72.2% 至 101.8% 的平均回收率，为采用质谱分析的液相色谱提供了 45.6% 至 87.0%。含药饲料的检测限范围为 4.2 至 10.7 mg kg ^-1（HPLC-DAD）和 5.6 至 10.8 mg kg ^-1用于 LC-MS。我们的实验表明，对于使用两种不同检测技术（例如 DAD 和 MS）的分析化合物，使用相同的萃取混合物，我们无法获得相同的回收率值。