In-situ pH measurement: A continuous flow analysis method for seawater pH determination using a ion sensitive field effect transistor (ISFET)

With the aim of adapting ISFET sensors to in-situ seawater pH monitoring, a continuous flow method was set up in the laboratory. The system used consists of a peristaltic pump, a two position valve and a measurement cell including the ISFET detector and a renewable junction reference electrode. The calibration and measurement procedure was achieved by alternating buffers and sample flowing over the detector. This enables the authors to eliminate inherent ISFET drift. The method was tested on acidified seawater samples of pH 8.00 to 7.38. Results obtained, with a resolution of 0.06 pH, are in good agreement with pH-metric measurements (using a glass electrode). This method could be utilized in an autonomous underwater system