Reagentless and calibrationless silicate measurement in oceanic waters

Area of Science:

• Environmental Science
• Analytical Chemistry
• Electrochemistry

Background:

• Accurate in situ determination of silicate in seawater is essential for autonomous monitoring.
• Existing methods often require liquid reagents and calibration, limiting autonomous applications.
• Developing reagentless, calibrationless methods is a key challenge for in situ sensors.

Purpose of the Study:

• To develop and validate a calibrationless electrochemical method for silicate determination in seawater.
• To assess the feasibility of using chronoamperometry on microelectrodes (ME) and ultramicroelectrodes (UME) for this purpose.
• To enable autonomous in situ silicate sensing without reagent addition.

Main Methods:

• Utilized successive chronoamperometry on planar microelectrodes (ME) and ultramicroelectrodes (UME).
• Employed a pair of gold disk electrodes for measurements.
• Tested the method with varying concentrations of silicate in artificial seawater (55–140×10⁻⁶ mol L⁻¹).

Main Results:

• The method successfully estimated diffusion coefficients and silicate concentrations simultaneously.
• Results for ferrocyanide showed excellent agreement with literature values.
• The calibrationless silicate method yielded good agreement between known and experimentally derived concentrations, with a diffusion coefficient of 2.2±0.4×10⁻⁶ cm² s⁻¹ for the silicomolybdic complex.

Conclusions:

• The developed chronoamperometric method offers a promising approach for calibrationless, reagentless silicate determination.
• This technique supports the development of autonomous in situ electrochemical silicate sensors.
• Future work will focus on extending the method to lower oceanic silicate concentration ranges.