Karl Fischer Water Testing - ASTM D6304, Procedure A, B and C

Which procedure should I request?

ASTM D6304 Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration has three procedures (all coulometric) for determining water content. The procedures can be used based on the sample itself, known interactions, and/or equipment availability. Savant Labs typically run ASTM D6304 Procedure B (which used to be Procedure C recently updated by ASTM) and Procedure A. The different procedures are highlighted below. 

The principle of Karl Fischer titration is based on the oxidation reaction between iodine and sulphur dioxide. Water reacts with iodine and sulphur dioxide to form sulphur trioxide and hydrogen iodide. An endpoint is reached when all the water is consumed.

Procedure A - is recommended only for low viscosity samples without expected interferences. A representative portion of the test specimen is injected directly into the titration cell.

Procedure B, Water Oven Accessory— is recommended for samples that do not readily dissolve in Karl Fischer reagent (reagent consists of iodine, sulfur dioxide, a base, and a solvent, such as alcohol), viscous samples, and samples with components that are expected to interfere with the Karl Fischer reaction. A representative portion of the sample is placed into a sealed glass vial and heated in an oven to extract any water present into the headspace of the vial. The vaporized water in the headspace is carried into the Karl Fischer titration cell by a dry non-reactive carrier gas where the water is titrated. Co-solvents may be used to enhance water extraction from the sample.

Procedure C, Water Evaporator Accessory— is also recommended for samples that do not readily dissolve in Karl Fischer reagent, viscous samples, and samples with components that are expected to interfere with the Karl Fischer reaction.  As in Procedure B, a representative portion of the test specimen is injected into a heated solvent or mineral oil in the water vaporizer accessory and the vaporized water is carried to the Karl Fischer cell by a dry non-reactive carrier gas where the water is titrated.

Procedures B and C can be used to analyze samples appropriate for Procedure A. Should you be unsure as to which method to select, our team of experienced technicians and chemists are here to assist you.