Standards

Q: What does ASTM D6304 measure?

D6304 reports water content by coulometric Karl Fischer titration, typically in mg/kg.

ASTM D6304 Karl Fischer Water Determination

ASTM D6304 is the coulometric Karl Fischer method for water in petroleum products, lubricating oils, and additives. Laboratories use it when they need a specific water number — usually in mg/kg — rather than a generic “moisture” loss on heating.

The method allows more than one way to get the water into the titration cell. Direct introduction works for many hydrocarbons. Other procedures heat the sample and sweep the released moisture into the cell with dry inert gas, which is the evaporator path used on oils that would foul a direct injection. Sulfur species such as mercaptans and sulfides can interfere, so a D6304 result is not automatically valid for every chemistry.

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ASTM Standard at a Glance

Property	Value
ASTM Standard	ASTM D6304
Type	Test method
Measures	Water by coulometric Karl Fischer titration
Applicable samples	Petroleum products, lubricating oils, additives
Related standards	Karl Fischer family (volumetric methods are separate)
Recommended equipment	VeroDry — Oil Moisture Analyzer

Choosing the right equipment for ASTM D6304

Coulometric Karl Fischer work is sensitive to cell condition, reagent quality, and how the water actually reaches the titrator. Oils that coat the electrode need the evaporator path, not a hopeful direct injection.

The Vero Scientific oil moisture analyzer (VeroDry) is the instrument linked to this method.

Frequently Asked Questions

What does ASTM D6304 measure?

D6304 reports water content in petroleum products, lubricating oils, and additives by coulometric Karl Fischer titration. Results are typically in mg/kg, with sample size chosen so the same method can cover higher concentrations.

What is coulometric Karl Fischer titration?

Karl Fischer titration measures water by a specific chemical reaction. The coulometric form generates the reagent in the cell and calculates water from the charge passed. It is not a loss-on-heating moisture method.

Does ASTM D6304 always inject the oil into the cell?

Some procedures inject the sample into the titration cell. Others heat the sample and sweep the released moisture into the cell with dry gas — the evaporator path used when the oil would foul a direct injection. Mercaptans, sulfides, and some other sulfur species are known interferences.

Does Vero Scientific provide equipment for ASTM D6304?

Yes. The oil moisture analyzer (VeroDry) is the Vero Scientific instrument for this Karl Fischer moisture workflow.

Is ASTM D6304 the same as a distillation water test?

No. D95 and D4006 are distillation / trap methods with a different range and a different set of interferences. Do not treat a D6304 number as interchangeable with those results without a written correlation.