Petroleum products and lubricants - Determination of acid or base number - Colour-indicator titration method (ISO 6618:1997)

2Scope / Description

This International Standard specifies a colorimetric indicator titration method for determining the acidic and basic components of mineral oil products soluble in a mixture of toluene and isopropanol. This method is suitable for determining acids and bases with dissociation constants greater than 10⁻⁹ in water. Very weak acids and bases with dissociation constants less than 10⁻⁹ do not interfere. A reaction occurs when the hydrolysis constant of a salt is greater than 10⁻⁹. This method is not suitable for determining the basic components of many types of lubricating oils containing basic additives. These components can be determined according to ISO 3771. This International Standard indicates the relative changes that occur in the oil during use under oxidizing conditions. Although the titration is performed under defined equilibrium conditions, this method does not provide absolute acid or basic values that can be used to predict the behavior of the oil in use. Oils that cannot be analyzed by this method due to the difficulty in identifying the titration endpoint, such as many cutting oils, rust-preventive oils, oils with similar compositions, or dark mineral oils, can be analyzed according to ISO 6619 (potential titration).