Testing the Honeywell Durafet® for seawater pH applications

Abstract

We report on the first seawater tests at 1 atm of the Honeywell Durafet ® pH sensor, a commercially available ion sensitive field effect transistor (ISFET). Performance of this sensor was evaluated in a number of different situations including a temperature-controlled calibration vessel, the MBARI test tank, shipboard underway mapping, and a surface mooring. Many of these tests included a secondary reference electrode in addition to the internal reference supplied with the stock Durafet sensor. We present a theoretical overview of sensor response using both types of reference electrode. The Durafet sensor operates with a short term precision of ± 0.0005 pH over periods of several hours and exhibits stability of better than 0.005 pH over periods of weeks to months. Our tests indicate that the Durafet pH sensor operates at a level of performance satisfactory for many types of biogeochemical studies at low pressure. *Corresponding author: E-mail: trmartz@ucsd.edu AcknowledgmentsThis work was supported by grants from the David and Lucile Packard Foundation and the National Science Foundation through the Biocomplexity in the Environment Program Grant ECS-0308070 and the Ocean Technology and Interdisciplinary Coordination Program Grant OTIC-0844394. We thank Bob Carlson at Honeywell Laboratories for many helpful discussions throughout this work and for a critical review of the manuscript. Gernot Friederich provided underway TCO 2 and pCO 2 data. Hans Jannasch, Luke Coletti, Tom Marion, and Jim Montgomery facilitated construction of the autonomous Durafet sensor. Ginger Elrod, Steve Fitzwater, and Carole Sakamoto performed spectrophotometric pH measurements on test tank samples.

Spatiotemporal Assessment of CO2–Carbonic Acid System Dynamics in a Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern Hawaiian Islands

“…These pairs were assumed to be representative of duplicates since the measurements were taken in the open ocean while transiting between islands. The mean difference for the pH electrode duplicates was ±0.0006, which is consistent with the findings of Martz et al (2010).…”

“…Experimental results indicate the DuraFET can operate with a short-term precision of ±0.0005 over several hours and a stability of ±0.005 over weeks to months (Martz et al 2010;Bresnahan et al 2014). Calibration samples were collected into borosilicate glass bottles, poisoned with 0.02% volume of saturated mercuric chloride and sealed with Apiezon grease (Dickson et al 2007).…”

Real-time estimation of pH and aragonite saturation state from Argo profiling floats: Prospects for an autonomous carbon observing strategy

“…The advent of new pH sensors [Seidel et al, 2008;Martz et al, 2010] and developing technologies for determination of a second carbon system parameter (R. H. Byrne et al, Sensors and systems for observations of marine CO 2 system variables, 2009, OceanObs09 community white paper, available at http://www.oceanobs09.net/blog/?p=253) will ultimately shed light on short-term variability, but currently these options have limited long-term, autonomous profiling capability. The inability to characterize natural variability of ocean carbon chemistry on a broad range of space and time scales therefore remains a hindrance to understanding organism and ecosystem thresholds and potential biogeochemical feedbacks within the carbonclimate system.…”

Exploring local adaptation and the ocean acidification seascape – studies in the California Current Large Marine Ecosystem

“…Prior to OMEGAS, however, no coordinated inner-shelf time series were available that would allow evaluation of the frequency, intensity and spatial expanse with which coastal ecosystems experience rapid acidification. The recent development of autonomously recording pH sensors (Martz et al, 2010) has helped to bridge this data gap. Easily deployed on either moorings or benthic (e.g., rocky intertidal) locations, these sensors facilitate the collection of environmental pH data in a variety of habitats and support the collection of long-term data sets that more comprehensively characterize the OA seascape .…”