ISO 5518:1978

The method consists in homogenizing the product, followed by dilution and acidification of a test portion, extraction of the acid by diethyl ether, then alkaline re-extraction of this acid and purifying by oxidation using acidified potassium dichromate, determination of the acid with a suitable spectrophotometer. The method cannot be applied in the presence of p-chlorobenzoic acid and cinnamic acid, respectively.