Deep-Sea DuraFET: A Pressure Tolerant pH Sensor Designed for Global Sensor Networks.

Increasing atmospheric carbon dioxide is driving a long-term decrease in ocean pH which is superimposed on daily to seasonal variability. These changes impact ecosystem processes, and they serve as a record of ecosystem metabolism. However, the temporal variability in pH is observed at only a few locations in the ocean because a ship is required to support pH observations of sufficient precision and accuracy. This paper describes a pressure tolerant Ion Sensitive Field Effect Transistor pH sensor that is based on the Honeywell Durafet ISFET die. When combined with a AgCl pseudoreference sensor that is immersed directly in seawater, the system is capable of operating for years at a time on platforms that cycle from depths of several km to the surface. The paper also describes the calibration scheme developed to allow calibrated pH measurements to be derived from the activity of HCl reported by the sensor system over the range of ocean pressure and temperature. Deployments on vertical profiling platforms enable self-calibration in deep waters where pH values are stable. Measurements with the sensor indicate that it is capable of reporting pH with an accuracy of 0.01 or better on the total proton scale and a precision over multiyear periods of 0.005. This system enables a global ocean observing system for ocean pH.

[1]  B. Carter,et al.  An automated system for spectrophotometric seawater pH measurements , 2013 .

[2]  Kenneth S Johnson,et al.  Chemical sensor networks for the aquatic environment. , 2007, Chemical reviews.

[3]  R. Lukas,et al.  Physical and biogeochemical modulation of ocean acidification in the central North Pacific , 2009, Proceedings of the National Academy of Sciences.

[4]  Xavier Llovet,et al.  Monte Carlo Simulation of Secondary Fluorescence in Small Particles and at Phase Boundaries , 2000, Microchimica Acta.

[5]  R. Feely,et al.  Evidence for Upwelling of Corrosive "Acidified" Water onto the Continental Shelf , 2008, Science.

[6]  Robert H. Byrne,et al.  Spectrophotometric seawater pH measurements: total hydrogen ion concentration scale calibration of m-cresol purple and at-sea results , 1993 .

[7]  E. Lewis,et al.  The practical salinity scale 1978 and its antecedents , 1980 .

[8]  J. F. Waters,et al.  The free proton concentration scale for seawater pH , 2013 .

[9]  D. Wallace,et al.  Program developed for CO{sub 2} system calculations , 1998 .

[10]  F. Millero The marine inorganic carbon cycle. , 2007, Chemical reviews.

[11]  D. O’Sullivan,et al.  Continual measurement of the total inorganic carbon in surface seawater , 1998 .

[12]  S. Riser,et al.  The Argo Program : observing the global ocean with profiling floats , 2009 .

[13]  R. Feely,et al.  Direct observations of basin‐wide acidification of the North Pacific Ocean , 2010 .

[14]  K. Daly,et al.  Technology for Ocean Acidification Research: Needs and Availability , 2015 .

[15]  Nicholas R. Bates,et al.  A Time-Series View of Changing Ocean Chemistry Due to Ocean Uptake of Anthropogenic CO2 and Ocean Acidification , 2014 .

[16]  Stephen C. Riser,et al.  Long-Term Nitrate Measurements in the Ocean Using the in situ Ultraviolet Spectrophotometer: Sensor Integration into the APEX Profiling Float , 2013 .

[17]  Kenneth S Johnson,et al.  Characterization of an ion sensitive field effect transistor and chloride ion selective electrodes for pH measurements in seawater. , 2014, Analytical chemistry.

[18]  Rainer Feistel,et al.  pH of seawater , 2011 .

[19]  Adina Paytan,et al.  High-Frequency Dynamics of Ocean pH: A Multi-Ecosystem Comparison , 2011, PloS one.

[20]  H. S. Harned,et al.  THE DISSOCIATION CONSTANT OF ACETIC ACID FROM 0 TO 35° CENTIGRADE1 , 1932 .

[21]  M. DeGrandpre,et al.  A submersible autonomous sensor for spectrophotometric pH measurements of natural waters. , 2003, Analytical chemistry.

[22]  Todd R. Martz,et al.  Testing the Honeywell Durafet® for seawater pH applications , 2010 .

[23]  Jens Zosel,et al.  Encapsulation of ISFET sensor chips , 2005 .

[24]  C. Culberson,et al.  EFFECT OF PRESSURE ON CARBONIC ACID, BORIC ACID, AND THE pH IN SEAWATER1 , 1968 .

[25]  R. Wanninkhof,et al.  Decadal acidification in the water masses of the Atlantic Ocean , 2015, Proceedings of the National Academy of Sciences.

[26]  Philip J. Bresnahan,et al.  Best practices for autonomous measurement of seawater pH with the Honeywell Durafet , 2014 .

[27]  K. H. Khoo,et al.  Determination of hydrogen ion concentrations in seawater from 5 to 40.degree.C: standard potentials at salinities from 20 to 45% , 1977 .

[28]  R. Feely,et al.  Real‐time estimation of pH and aragonite saturation state from Argo profiling floats: Prospects for an autonomous carbon observing strategy , 2011 .

[29]  Piet Bergveld,et al.  Thirty years of ISFETOLOGY ☆: What happened in the past 30 years and what may happen in the next 30 years , 2003 .

[30]  A. Dickson Standard potential of the reaction: , and and the standard acidity constant of the ion HSO4− in synthetic sea water from 273.15 to 318.15 K , 1990 .

[31]  Francesco Pomati,et al.  Potentiometric sensing array for monitoring aquatic systems. , 2015, Environmental science. Processes & impacts.