First Deployment and Validation of in Situ Silicate Electrochemical Sensor in Seawater

Abstract

An electrochemical sensor is proposed to measure silicate concentration, in situ, in the ocean without any addition of liquid reagent. From the analytical principle to the laboratory prototype toward the first in situ, immersible sensor, the evolution of the mechanical design is presented and discussed. The developed in situ electronics were compared to the commercial potentiostat and gave promising results to detect low silicate signals with a limit of quantification of 1 µmol L −1 .The flow rate of the pump appeared to be a crucial parameter in order to transfer the silicomolybdic complex formed from the "complexation cell" to the "detection cell" without dilution as well as to fill and rinse the whole circuit. The study of temperature effect revealed no influence on the electrochemical signal between ∼7 • and ∼21 • C. Finally the sensor was successfully deployed for the very first time on a mooring off Coquimbo, Chile and also integrated onto a PROVOR profiling float in the Mediterranean Sea off Villefranche-sur-Mer, France. The data collected and/or sent through satellite were in good agreement with the 2 reference samples and previously published values illustrating the great potential of this electrochemical sensor. A 7 days silicate time series from the mooring deployment off Chile is also presented.

Electrochemical monitoring of marine nutrients: From principle to application

“…A submersible in situ electrochemical sensor was developed, based on the use of molybdosilicate for long-time monitoring of silicate without the need for additional reagents [131]. As presented in Fig.…”

Toward a Harmonization for Using in situ Nutrient Sensors in the Marine Environment

“…Electrochemistry proposes promising reagentless sensors that could facilitate miniaturization and decrease energy requirements (Lacombe et al, 2008). Electrochemical methods have been developed to detect silicate (Barus et al, 2016(Barus et al, , 2018 and phosphate (Jońca et al, 2011(Jońca et al, , 2013 in seawater. As silicate and phosphate are non-electroactive compounds, a chemical reaction with molybdates under acidic pH is required to transform these nutrients into silico-and phospho-molybdic complexes.…”

“…The method has the benefit to be robust and simple because based on straightforward sample fluidics with no liquid reagent (Table 2). However, although the electrochemical reaction is performed in few seconds, the total measurement time is about 30 min due to a rather slow pumping technology (Barus et al, 2018).…”

“…These sensors are considered more suitable for long-term deployments on moored/buoy platforms. At the present time, only one silicate prototype (ANESIS, Barus et al, 2018) has been implemented on moorings off shore as well as on profiling float.…”

Advancing Observation of Ocean Biogeochemistry, Biology, and Ecosystems With Cost-Effective in situ Sensing Technologies

“…been validated for seawater use (Barus et al, 2018). This latter instrument utilizes a two-cell configuration (complexation with molybdenum, detection using gold working and silver reference electrodes) and achieves a micromolar detection limit, has a sampling period of approximately 1 h, is small in size (100 mm diameter, 186 mm height packaged), and has a low power consumption (25 mAh for 1 sample per hour).…”