Electrochemical determination of water in environmental hydraulic fluids using the karl Fischer reaction

Different procedures based on the Karl Fischer reaction were investigated with respect to their applicability for water determinations in environmental hydraulic fluids: (i) continuous coulometry using a recently described diaphragm-free cell; (ii) on-line stripping of water at elevated temperature using either continuous coulometry or direct potentiometry for detection of the liberated water. Except for one of the oils, Statoil PA, which is a poly(α-olefin) with certain polymers added, no significant difference was found among coulometry using an optimized imidazole-buffered methanolic reagent containing 75% (v/v) chloroform, the two different stripping techniques (working in the temperature interval 100-110 °C), and the commercially available Hydranal Coulomat AG-H. The high stability and sensitivity of the coulometric technique described made it possible to work with sample amounts in the low milligram-range, and this is shown to increase the reliability of the coulometric method as compared to normally used procedures.