This International Standard specifies a semi-micro colour-indicator method for the determination of acidic constituents in new or used petroleum products and lubricants soluble in mixtures of toluene and propan-2-01, or capable of existing as suspensions in such mixtures, and where the suspended material is sufficiently dissociated that its acidic components can be titrated.

The method is especially intended for applications in which the amount of sample available to be analysed is too small to allow accurate analysis by ISO 6619 or ISO 6618. It is applicable to the determination of acids having dissociation constants in water larger than 10⁻⁹. Extremely weak acids having dissociation constants smaller than 10⁻⁹ do not interfere. Salts titrate if their hydrolysis constants are larger than 10⁻⁹.