Potentiometric Water Sensor For Eutectic Solvents Containing Choline Chloride and Ethylene Glycol.

Area of Science:

• Electrochemistry
• Materials Science
• Environmental Science

Background:

• Eutectic solvents (ESs) are cost-effective and environmentally friendly for metal reprocessing.
• Moisture absorption by ESs significantly impacts electrochemical recovery processes.
• Choline chloride:ethylene glycol (ChCl:2EG) is a widely used ES with known hygroscopic properties.

Purpose of the Study:

• To develop and validate a novel electrochemical method for quantifying atmospheric water content in ChCl:2EG.
• To assess the water uptake of ChCl:2EG over an 8-day period of atmospheric exposure.
• To establish a user-friendly, in situ method independent of external reference electrodes.

Main Methods:

• Exposing ChCl:2EG with initial 10 mM Cu²⁺ to open atmosphere for 8 days.
• Employing cyclic voltammetry to analyze the relative reduction potentials of Cu²⁺/⁺ and Cu⁺/⁰ redox couples.
• Utilizing a calibration plot derived from external reference samples to determine water content.

Main Results:

• A maximum water content of approximately 35% was observed after 8 days of atmospheric exposure.
• The method relies on the potential difference between two in situ formed redox couples, not absolute potentials.
• The developed method proved to be independent of the reference electrode choice.

Conclusions:

• The novel electrochemical method accurately quantifies water content in ChCl:2EG.
• This in situ potentiometric approach offers a user-friendly alternative for monitoring ES moisture.
• The methodology shows potential for generalization to other eutectic solvents for water content determination.