Field Performance of an ISFET based Profiling pH Sensor

Charles William Branham1, Vladislav Simontov1, Yuichiro Takeshita2 and David J Murphy1, (1)Sea-Bird Scientific, R&D, Bellevue, WA, United States, (2)Monterey Bay Aquarium Research Institute, Moss Landing, CA, United States
Spectrophotometry is the gold standard for measuring the pH of seawater from a shipboard CTD cast, but this method is expensive, labor intensive, and can only be measured at depths where bottle samples were taken. Ion Sensitive Field-Effect Transistor (ISFET) pH sensors offer many advantages over spectrophotometry especially for autonomous applications, and has been recently adapted for shallow and deep ocean monitoring on profiling floats, gliders, and moorings. Sea-Bird has expanded its use into new applications by developing an ISFET based pH sensor for shipboard profiling CTDs. This new pH sensor records data at 1 Hertz and integrates into Sea-Bird’s current CTD packages, like the SBE25 and SBE9. This presentation will focus on calibration of the ISFET pH sensor, evaluation of its analytical performance, and validation of the performance down to 2000 m by comparing sensor output to discrete samples analyzed by spectrophotometry.