Simultaneous Measurement of Total Ammonia Nitrogen and Free Ammonia via Integrated Electrochemical Acidification─Optode Flow Cell

Abstract

The accurate measurement of total ammonia nitrogen (TAN) and free ammonia is crucial for various environmental, biomedical and industrial applications. We present a novel integrated system combining electrochemical water splitting with ammonia optodes to simultaneously measure TAN and free ammonia. Water electrolysis induces localized pH shifts, altering the ammonia speciation in the sample solution: an increase in pH near the cathode leads to conversion of NH₄⁺ to NH₃, enabling the measurement of TAN. Concurrently, a decrease in pH near the anode reduces the NH₃ concentration to zero, enabling real-time zero calibration. In areas unaffected by these pH changes, the optode readout can effectively measure free NH₃. The system demonstrates a measurement range of 0-300 mg·L^-1 for both TAN and NH₃, with a complete measurement cycle requiring only 6 min. The method was validated through the analysis of urine samples, showcasing its potential for real-time monitoring in clinical and environmental settings. The electrochemical speciation shifting allows for precise TAN measurement, while the zero-point calibration provided by the anode enhances the method's robustness and reliability. Overall, this study introduces a versatile and efficient approach for the simultaneous determination of TAN and NH₃, offering significant improvements in speed and operational simplicity.