Thermal stability assessment of antibiotics in moderate temperature and subcritical water using a pressurized dynamic flow-through system

Thermal degradation of antibiotics has been studied for decades in a broad range of disciplines including food production, agriculture and analytical chemistry. Yet, there is a lack of thermal stability data for many antibiotics. Here we systematically investigated the thermal stability of ten commonly prescribed antibiotics applying a laborsaving automated inhouse pressurized dynamic flow-through system. The design of the system allowed a fast access to a large number of data at medium to subcritical water temperatures, ranging from 50-250 °C. The five ß-lactams cefadroxil, cefuroxime, amoxicillin, penicillin V, and penicillin G showed a high degree of stability with a maximum degradation of less than 30 % at 150 °C. The two quinolones ciprofloxacin and norfloxacin showed a very high thermal stability up to 200 °C, as did trimethoprim and sulfamethoxazole. At 250 °C all antibiotics were either partly of fully removed. The tetracycline doxycycline showed a specific removal pattern probably involving both binding to metal surfaces at lower temperatures as well as degradation at increased temperatures.