Ocean pH sensor technology has advanced quickly over the last few years. This is predominately driven by the integration of Honeywell™ Durafet® pH electrodes in oceanographic sensor packages. Durafets sensors contain Ion Sensitive Field Effect Transistor (ISFET) technology, which produces highly precise pH measurements in seawater. Precision is better than 0.005 units pHT and stability of the calibration can be maintained for several months (Martz et al. 2010; Takeshita et al. 2014). These characteristics have made Durafet-based sensors popular among oceanographers and marine biologists alike.
Since 2010, multiple Durafet-based pH sensors have become commercially available. Sensors are currently used in estuarine, coastal, and deep-sea ecosystems, underway measurements, profiling floats, and laboratory-based ocean acidification experiments. Durafet-based sensors require specialized expertise for optimal operation and high-quality data acquisition (McLaughlin et al. 2017). The crux of data quality lies in the intricacies associated with calibration of these sensors. While commercial sensors have a factory calibration, this may not be accurate enough for certain marine applications (Figure 1). Most often, users need to perform a calibration using multiple, independent, seawater samples which are then analyzed for pH in the laboratory and used in data processing (Bresnahan et al. 2014). Using such reference samples for calibration, and following proper maintenance, a single SeaFET™ pH sensor can produce high-quality data for multiple years in a coastal environment (Kapsenberg et al. 2017a). Currently, data quality varies among user groups and is associated with experience level (McLaughlin et al. 2017). For this reason, hands-on training provides a beneficial supplement to recently published best practices (Bresnahan et al. 2014; Kapsenberg et al. 2017b; Rivest et al. 2016).
Kapsenberg L., 2017. Workshop on Durafet-based pH sensors highlights importance of collecting reference samples. Limnology and Oceanography Bulletin 27 (1): 26-28. Article.