Real-time monitoring of ciprofloxacin degradation in an electro-Fenton-like system using electrochemical-mass spectrometry†
Electro-Fenton-like processes are widely used in removal of antibiotics in sewage owing to their excellent degradation efficiency for organics. However, the degradation mechanisms of antibiotics in electro-Fenton-like systems are still unclear caused by the non-real time detection of current methods. An electrochemical-mass spectrometry (EC-MS) method was developed for in situ analysis and real-time monitoring of electrochemical degradation of antibiotics in this study. In EC-MS, ITO glass was used as an electrochemical reactor and counter electrode, which is positioned in front of the MS inlet. A platinum slice as a working electrode was placed over the ITO glass. When different high voltages were applied on the electrodes, the electrochemical degradation of organics started and a charged spray was generated for MS detection. To enhance the electrochemical reaction efficiency, the voltage difference was optimized. As a proof-of-concept, the degradation of ciprofloxacin (CIP) in an electro-Fenton-like system was monitored, and five intermediates (m/z 330, 304, 348, 346 and 362) different from those obtained in other removal processes were detected and verified. Furthermore, six new characteristic intermediates (m/z 364, 305, 293, 277, 275 and 280) were captured. Meanwhile, the compounds were identified by high-resolution mass spectrometry and tandem mass spectrometry. Extracted ion chromatography (EIC) of several characteristic intermediates was performed for further discussion of the degradation pathway. Based on the data acquired, the degradation mechanism of CIP by an electro-Fenton-like process was proposed for the first time. This work provided a useful tool for mechanism research in electrochemical advanced oxidation processes.