ASTM D4377: Water Content, Karl Fischer (potentiometric) grease & oil

ASTM D4377 Water in Crude Oils by Potentiometric Karl Fischer Titration

Water may be detrimental to lubricants. It may catalyze oxidation, lessen anti-corrosion properties, cause precipitation of additives and change viscosities, dielectric constants, and resistivity values. It is therefore desirable to know the water content of a lubricant.

This method measures water content of lubricants using the Karl Fischer reaction. The sample is combined with the appropriate reagents and the Karl Fisher (iodine-containing) reagent is titrated into the mixture. The percent water by weight is reported.

Choosing a water content test: Petro-Lubricant Testing Laboratories offers several tests to determine water contents: Consider a coulometric method (ASTM D6304) when very low levels of water are predicted (10 to 25,000 ppm). Consider a potentiometric method (such as ASTM D4377 (this method)) when slightly higher levels of water are predicted (0.2 to 2%). Consider a distillation method (ASTM D95) for higher levels of water (up to 25%). Consider the centrifuge method (ASTM D1796) for even higher levels of water (up to 30%) or if both water and sediment are of interest: If volumetric information is desired, consider ASTM E203 "Water Using Volumetric Karl Fischer Titration". For volatile solvents consider ASTM D1364 "Water in Volatile Solvents (Fischer Reagent Titration Method)".