In-situ Chemical Measurements at Deep-Sea and
The image above shows the prototype ISE sensor array undergoing in-situ testing in April 2012 on a cruise starting at Franklin Bridge in Philadelphia, down the Delaware River, and then 10 miles off-shore.
In summary, the immediate goal of the proposed work was to develop and demonstrate as a proof-of-concept a sensor array capable of providing simultaneous in-situ real-time nM-mM measurements of ionic species, initially including Na+, K+, Mg2+, Ca2+, NO3-, NH4+, H+, S2-, F-, and Cl-, at extreme depths in seawater. The longer-term objective was to enable follow-on research that, with improved detection limits and selectivity, would provide the ocean sciences community with a new tool for in-situ real-time chemical mapping of a broad range of ionic chemical species in seawater. The proposed effort was divided over two years (2011-2013). During the first year our goal was to design, purchase, fabricate, test, integrate, and field test, a prototype sensor array in easily accessible location traversing fresh and sea water domains. During the second year, building on lessons learned from the first-year evaluation, we made modifications and demonstrated that the sensor array can provide reliable/accurate real-time chemical analyses during cruises in coastal waters (~ 2700m) off of Delaware. We successfully fabricated a subset of the ion selective (ISE) sensors. They have been tested in the lab in a custom-built high-pressure chamber up to 160 bar and in seawater collected during an August cruise from surface to a 2700m depth. In addition, the sensors were also evaluated during a cruise (3/31- 4/3/2012) in Delaware Bay over a 177 km transect starting 26 km south of Franklin Bridge (Philadelphia PA) and ending 20 km offshore from the mouth of Delaware Bay in open ocean. The results show that the prototype ISE sensors are capable of accurately measuring concentrations of the proposed ionic species at pressures up to 160 bar and in real seawater samples. We have shown for the first time the potential ability to use ion selective electrodes (ISE) to obtain in-situ concentrations of several inorganic ionic species, but most importantly shown by comparisons with two other NO3- analytical techniques, that we can detect variations of nitrate at ambient concentrations in the micro-molar range in seawater.
A more detailed report of our results can be found HERE.
 "Solid Contact Ion Selective Electrodes for In Situ Measurements at High Pressure" A. W. Weber, G. D. O'Neil, and S. P. Kounaves, Anal. Chem., 2017, 89, 4803-4807, doi: 10.1021/acs.analchem.7b00366. Full Text