A Novel Method for Determining Substances That Interfere With the Measurement of Water in Oils and Other Chemicals by the Karl Fischer Methods
S A. Margolis, J L. Paulson, E T. Park
A coulometric method has been developed and validated for the measurement of substances that interfere with the Karl Fischer method for the determination of water by reacting with iodine or iodide. This method was calibrated with 0.1 mol/L sodium thiosulfate. The S02-free reagent that has been developed reacts quantitatively with cysteine and ascorbic acid but does not react with vinyl acetate. A series of oils including five transformer oils (including RM 8506 and RM 8507), a high and a low sulfur crude oil (SRM 2721 and SRM 2722), a white oil, a high vacuum oil and a high viscosity base stock oil have been evaluated. One oil contained less than 10 mg/kg (water equivalents of interfering substances in oil) and two oils(RM 8507 and Drakeol 35)contained no measurable amounts of interfering material. SRM 2271, a sour crude oil contained 834 (SD = 25) mg/kg (water equivalents of interfering substances in oil). Approximately 20% of this material was volatile and an additional 20% appeared to undergo some degradation (possibly oxidation) once the oil was exposed to air. These results indicate that this method is a general method for measuring substances that react with iodine and that it is capable of measuring in a variety of oils interfering substances that inflate moisture measurements.
coulometry, crude oils, interfering subtances, Karl Fischer, transformer oils
, Paulson, J.
and Park, E.
A Novel Method for Determining Substances That Interfere With the Measurement of Water in Oils and Other Chemicals by the Karl Fischer Methods, Analytical Chemistry
(Accessed June 7, 2023)