BS EN ISO 4629-1:2016 pdf download.Binders for paints and varnishes-Determination of hydroxyl value Part 1: Titrimetric method without using acatalyst
5 Reagents
During the analysis,use only reagents of recognized analytical grade and only water of at least grade 3purity as specified in ISo 3696.
5.1 Potassium hydrogen phthalate [C6Ha(COOH) (COOK)].5.2 Ethyl acetate, anhydrous.
5.3Toluene/butanol mixture,1 + 2 by volume.5.4Pyridine/water mixture,3 + 1 by volume.5.5Acetylating reagent.
Dissolve 4,0g of p-toluenesulfonic acid monohydrate (CHaC6HaSOgHH20) in 100 mlofethylacetate(5.2),preferably using a magnetic stirrer.
To this solution, add slowly, while stirring, 33 ml of acetic anhydride.Check that 5 ml of this reagentrequires on titration a volume of between 40 ml and 50 ml of potassium hydroxide solution (5.6) forneutralization.
5.6Potassium hydroxide, standard volumetric solution, c(KOH) ~ 0,5 mol/l, in methanol.Ethanol may also be used if the product to be tested is soluble in ethanol.
5.6.1 Preparation
Weigh, to the nearest 0,05 g,.28 g of potassium hydroxide, dissolve in the minimum quantity of water ina 1000 ml one-mark flask, dilute to the mark with methanol and mix well.
5.6.2 Standardization
Weigh, to the nearest 0,01 g, 2,.5 g of potassium hydrogen phthalate (5.1), previously dried at about120 °C to constant mass and allowed to cool in a desiccator, into a 250 ml flask. Add 150 ml freshlyboiled and cooled water and swirl until dissolved.
Titrate the potassium hydroxide solution prepared in 5.6.1, using phenolphthalein solution (5.7) asindication, until a red coloration that remains for at least 10 s appears.
Calculate the actual concentration, c, in moles of hydroxyl ions (OH) per litre, of the potassiumhydroxide solution, using Formula (1).
