ISO 660:2009 pdf free download – Animal and vegetable fats and oils – Determination of acid value and acidity.
4 Principle
The sample is dissolved in a suitable solvent mixture, and the acids present are titrated with an ethanolic or methanolic solution of potassium or sodium hydroxide.
The methods specified in 9.1 and 9.2 are reference methods.
5 Reagents
WARNING — Attention is drawn to the regulations which specify the handling of hazardous substances. Technical, organizational and personal safety measures shall be followed.
Use only reagents of recognized analytical grade, unless otherwise specified.
5.1 Solvent A for solvent mixture (5.3): ethanol, volume fraction, p 96 %.
As a replacement, propan-2-ol, volume fraction, p 99 %, can be used.
5.2 Solvent B for solvent mixture (5.3): diethyl ether, peroxide-free.
As a replacement, tert-butyl methyl ether, light petroleum (boiling range 40 °C to 60 °C) or toluene can be used.
WARNING — Diethyl ether is very flammable and may form explosive peroxides. Use with great caution.
5.3 Solvent mixture, mix equal volumes of solvent A and B, (e.g. c’A = 50 ml/100 ml and = 50 ml/l 00 ml).
For hard or animal fats, a solvent mixture of one volume of solvent A (e.g. 25 ml) and three volumes of tertbutyl methyl ether or toluene (e.g. 75 ml) is recommended.
Neutralize, just before use, by adding potassium hydroxide solution in the presence of 0,3 ml of the phenolphthalein solution per 100 ml of solvent mixture.
For the titration with aqueous KOH, the solvent propan-2-ol can be used.
5.4 Ethanol or methanol, of minimum volume fraction, , = 95 %.
5.5 Sodium hydroxide or potassium hydroxide, ethanolic or methanolic standard volumetric solutions, amount of substance concentration c(NaOH) or c(KOH) = 0,1 mol/l and 0,5 mol/l. The concentration shall be checked with a standard volumetric HCI solution.
9.2 Cold solvent method using potentiometnc titration (Reference method)
9.2.1 According to Table 1. weigh the test portion into a 150 ml beaker.
9.2.2 Add 50 ml to 100 ml of the neutralized solvent mixture (5.3) and dissolve the sample, if necessary with gentle warming.
For high melting point samples, use an ethanol-toluene mixture.
9.2.3 Introduce the combined electrode in the solvent mixture and connect it with the automatic titration apparatus.
9.2.4 Start the stirrer for at least 30 s and then titrate with constant swirling using standard potassium hydroxide solution (5.5).
9.2.5 As soon as the equivalence point is reached, record the amount of standard solution used.
9.3 Hot ethanol method using indicator
9.3.1 Under the conditions specified in this method, short-clain fatty acids, If present, are volatile.
9.3.2 Weigh into a flask a sufficient mass of the test sample as shown in Table 1, according to the colour and expected acid value.
9.3.3 Heat to boiling 50 ml of the ethanol containing 0,5 ml of the phenolphthalein indicator in a second flask. While the temperature of the ethanol is still above 70 C, neutralize it carefully with a solution of 0,1 molll sodium or potassium hydroxide.
The endpoint of the titration is reached when the addition of a single drop of alkali produces a slight but definite colour change persisting for at least 15 s.
Larger volumes of ethanol and indicator may be necessary for dark-coloured fats. Moreover, for dark-coloured fats, alkali blue or thymolphthalein shall be used.
9.3.4 Add the neutralized ethanol to the test portion in the first flask and mix thoroughly. Bring the contents to the boil and titrate with the sodium or potassium hydroxide solution, agitating the flask contents vigorously during the titration.