# The Preservatives in Food Regulations 1989, Paragraph 2: Principle


After distillation in an acid medium and extraction by di-isopentyl ether, the extract is purified and treated with a solution of 4-aminophenazone. A red colour develops, the intensity of which is measured spectrophotometrically at 510 nm.

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Source: https://www.legislation.gov.uk/uksi/1989/533/schedule/5/part/III/paragraph/2 (the official version)
Page: https://openlegislation.uk/preservatives-in-food-regulations-1989/schedule-5/part-III/paragraph-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.