Absorption of Water into Organic Solvents Used for Electrochemistry under Conventional Operating Conditions

Many solvents used for electrochemistry can be dried to <1 x 10(-3) M water content by storing the solvents over 3 angstrom molecular sieves in a nitrogen or argon atmosphere. However, as soon as the solvents are placed in an electrochemical cell, the water content increases significantly. Karl Fischer coulometric titrations were conducted on several predried solvents commonly used for electrochemistry (acetonitrile, dichloromethane, N,N-dimethylformamide, and dimethyl sulfoxide) in a controlled-humidity environment (30%, 50%, and 70% relative humidity) to determine the rate of moisture uptake into the organic solvents when used under typical electrochemical conditions (either in an electrochemical cell under a nitrogen atmosphere or in an electrochemical cell directly exposed to the atmosphere). The results in this study give guidelines for estimating the water content of organic solvents under conventional electrochemical operating conditions.