# Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996, Paragraph 3: REAGENTS


Distilled or demineralised water, free from carbon dioxide.
Buffer solution, pH 6.88 at 20°C
3.1 Dissolve 3.40 ± 0.01 grams of potassium dihydrogen orthophosphate (KH2PO4) in approximately 400 ml of water. Then dissolve 3.55 ± 0.01 gram of disodium hydrogen orthophosphate (Na2HPO4) in approximately 400 ml of water. Transfer the two solutions without loss into a 1 litre graduated flask, make up to the mark and mix. Keep the solution in an airtight vessel.
Buffer solution, pH 4.00 at 20°C
3.2 Dissolve 10.21 ± 0.01 grams of potassium hydrogen phthalate (KHC8O4H4) in water, transfer without loss into a 1 litre standard flask, make up to the mark and mix.
Keep this solution in an airtight vessel.
3.3 Commercially available pH standard solutions may be used.

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Source: https://www.legislation.gov.uk/nisr/1996/513/schedule/2/part/I/chapter/14d./paragraph/3 (the official version)
Page: https://openlegislation.uk/fertilisers-sampling-and-analysis-regulations-northern-ireland-1996/schedule-2/part-I/chapter-14d./paragraph-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.