On-line direct potentiometry of residual water in organic solvents using cells without a liquid junction under proton isoconcentration conditions

Abstract

A laboratory prototype monitor, based on direct potentiometry, was applied to the determination of residual water in organic solvents using cells without a liquid junction under proton isoconcentration conditions. In the monitor, a sample stream is bled off and mixed with a buffer before passing through a cell containing a pH glass electrode, a solid-state chloride electrode and an automatic temperature compensation probe. The instrument is calibrated with standard solutions containing water in the same solvent. The system is controlled by a program running on a general-purpose minicomputer. Results obtained for residual water in methanol, ethanol, propan-1-ol and propan-2-ol are accurate, reproducible and sensitive with an average response time of 5 min, and are superior to those obtained with the same monitor using cells with a liquid junction.