# First Commission Directive of 26 July 1979 laying down Community methods of analysis for testing certain sugars intended for human consumption (79/796/EEC), Division 6.1: Standardization of the Luff-Schoorl reagent (4.3)

Extent: E+W+S+N.I.

6.1.1. To 25 ml of Luff-Schoorl reagent (4.3) add 3 g of potassium iodide and 25 ml of 3 mol/litre sulphuric acid (4.6).
Titrate with 0·1 mol/litre sodium thiosulphate (4.4) using starch solution (4.5) as indicator added towards the end of the titration. If the volume of 0·1 mol/litre sodium thiosulphate used is not 25 ml the reagent must be made up afresh.
6.1.2. Pipette 10 ml of the reagent into a 100 ml volumetric flask and dilute to volume with water.
Pipette 10 ml of the diluted reagent into 25 ml of 0·1 mol/litre hydrochloric acid (4.11) in a conical flask and heat for one hour in a boiling water-bath. Cool, make up to the original volume with freshly boiled water and titrate with 0·1 mol/litre sodium hydroxide (4.10) using phenolphthalein (4.12) as indicator.
The volume of 0·1 mol/litre sodium hydroxide (4.10) used must be between 5·5 and 6·5 ml.
6.1.3. Titrate 10 ml of the diluted reagent (6.1.2) with 0·1 mol/litre hydrochloric acid (4.11) using phenolphthalein (4.12) as indicator. The end-point is characterized by the disappearance of the violet colour.
The volume of 0·1 mol/litre hydrochloric acid (4.11) used must be between 6·0 and 7·5 ml.
6.1.4. The pH of the Luff-Schoorl reagent must be between 9·3 and 9·4 at 20 oC.

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Source: https://www.legislation.gov.uk/eudr/1979/796/annex/II/division/7/division/6/division/6.1 (the official version)
Page: https://openlegislation.uk/eu-directive-1979-796/annex-II/division-7/division-6/division-6.1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.