Robust and sensitive analysis of methanol and ethanol from cellulose degradation in mineral oils.

Methanol and ethanol have been identified as oil-soluble by-products generated by the aging of oil-impregnated cellulosic insulation materials of power transformers. Their presence provides useful information for diagnostics and end-of-life transformer estimation. Despite their value as cellulose degradation indicators, their sensitive and accurate determination is challenged by the complex oil matrix.

Efficiency of methods for Karl Fischer determination of water in oils based on oven evaporation and azeotropic distillation.

The efficiency of azeotropic distillation and oven evaporation techniques for trace determination of water in oils has recently been questioned by the National Institute of Standards and Technology (NIST), on the basis of measurements of the residual water found after the extraction step. The results were obtained by volumetric Karl Fischer (KF) titration in a medium containing a large excess of chloroform (> or = 65%), a proposed prerequisite to ensure complete release of water from the oil matrix. In this work, the extent of this residual water was studied by means of a direct zero-current potentiometric technique using a KF medium containing more than 80% chloroform, which is well above the concentration recommended by NIST.