# The Feeding Stuffs (Sampling and Analysis) Regulations 1999, Paragraph 3: Reagents


3.1 Sodium hydroxide solution: dissolve 50 g sodium hydroxide in 50 ml water, mix well and store in a suitable plastic container.
3.2 Formaldehyde solution: the strength of the commercially available solution should be checked as follows: mix 3 ml formaldehyde solution with 50 ml IN sodium hydroxide solution and 25 ml hydrogen peroxide solution (20 volumes). Heat on a steam bath until effervescence stops. Cool, and titrate with IN hydrochloric acid using phenolphthalein indicator. Carry out a blank titration using 3 ml water in place of the formaldehyde.
1 ml of 1N sodium hydroxide ≡ 0.0300 g formaldehyde
strength of formaldehyde solution≡(B-T)× 0.0300×1003per 100 ml
where B = blank titre; and
T = sample titre.
3.3 Neutral ethanolic formaldehyde solution: mix an appropriate volume of formaldehyde solution (3.2) containing 17.5 g of formaldehyde with 250 ml water and 500 ml ethanol. Adjust the pH of the solution to 7.0 with 0.1N sodium bhydroxide solution. Dilute to 1,000 ml with water, mix and gain adjust the pH to 7.0 if necessary.
3.4 Scucinate buffer solution: dissolve by heating, 29.5 g of succinic acid in 750 ml water and 20 ml sodium hydroxide solution (3.1). Cool, add an appropriate volume of formaldehyde solution (3.2) containing 17.5 g of formaldehyde, mix well and adjust the pH to 6.0 with sodium hydorxide solution (3.1). Dilute to 1,000 ml with water, mix and gain adjust the pH to 6.0 if necessary.
3.5 sodium thiosulphate solution: 25 g sodium thiosulphate (Na2S2O3.5H2O) per 1,000 ml.
3.6 Silver lactate solution: dissolve, by heating, 3 g silver lactate in 50 ml water and 1 ml lactic acid. Dilute to 100 ml with water, filter, and store in dark glassware. Do not expose to strong light.
3.7 Ammoniacal magnesium solution: dissolve 8.75 g magnesium sulphate (MgSO4.7H2O) and 17.5 g ammonium chloride in 50 ml water. Add 30 ml ammonia solution (d = 0.88 g/ml) mix well and dilute to 100 ml with water.
3.8 Benedict and Hitchcock reagent: mix 35 ml silver lactate solution (3.6) with 15 ml ammoniacal magnesium solution (3.7). Add 50 ml ammonia solution (d = 0.88 g /ml). Mix well, Prepare immediately before use.
3.9 Standard uric acid solution: weigh to the nearest 0.1 mg, 250 mg of uric acid and transfer to a 150 ml round-bottomed flask fitted with a reflux condenser. Add 100 ml ethanolic formaldehyde solution (3.3) and boil under reflux on a steam bath for 30 minutes, shaking frequently. Cool, transfer the solution to a 250 ml graduated flask, wash the round-bottomed flask with ethanolic formaldehyde solution (3.3) and combine the washings with the uric acid solution. Dilute to the mark with ethanolic formaldehyde solution (3.3) and mix. 1 ml contains 1 mg of uric acid.
3.10 Light petroleum, boiling range 40–60°C.

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Source: https://www.legislation.gov.uk/uksi/1999/1663/schedule/2/part/4/paragraph/3 (the official version)
Page: https://openlegislation.uk/feeding-stuffs-sampling-and-analysis-regulations-1999/schedule-2/part-4/paragraph-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.