Characterization of an Ion Sensitive Field Effect Transistor and Chloride Ion Selective Electrodes for pH Measurements in Seawater

Characterization of several potentiometric cells without a liquid junction has been carried out in universal buffer, aqueous HCl, and artificial seawater media. The electrodes studied include Ion Sensitive Field Effect Transistor (ISFET) PH electrodes, and Chloride-Ion Selective Electrodes (CI-ISE) directly exposed to the solution. These electrodes were compared directly to the conventional hydrogen electrode and silver-silver chloride electrode in order to report the degree to which they obey ideal Nernstian laws. These data provide a foundation for operating the ISFETICI-ISE pair in seawater as a pH sensor. In order to obtain the highest quality pH measurements from this sensor, its response to changes in pH and salinity must be properly characterized. Our results indicate near-ideal Nernstiaii response for both electrodes over a wide range of pH (2-12) and Cl- molality (0.01-1). We conclude that the error due to sub-Nemstian response of the cell ISFETIseawaterICI-ISE over the range of seawater pH and salinity is negligible (<0.0001 pH). The cross sensitivity of the Cl-ISE, to Br- does not seem to be a significant source of error (<0.003 pH) in seawater Media in the salinity range 20-35.