ISO 3657:2020 pdf download Animal and vegetable fats and oils – Determination of saponification value (ISO 3657:2020)
1Scope
This document specifies a method for the determination of the saponification value of animal andvegetable fats and oils.The saponification value is a measure of the free and esterified acids present infats and fatty acids.
The method is applicable to refined and crude vegetable and animal fats.
lf mineral acids are present, the results given by this method are not interpretable unless the mineralacids are determined separately.
The saponification value can also be calculated from fatty acid data obtained by gas chromatographyanalysis as given in Annex B.For this calculation, it is necessary to be sure that the sample does notcontain major impurities or is thermally degraded.
2Normative references
The following documents are referred to in the text in such a way that some or all of their contentconstitutes requirements of this document.For dated references, only the edition cited applies.Forundated references, the latest edition of the referenced document (including any amendments) applies.Is0 661,Animal and vegetable fats and oils — Preparation of test sample
3Terms and definitions
For the purposes of this document, the following terms and definitions apply.
lSO and IEC maintain terminological databases for use in standardization at the following addresses:-ISO online browsing platform: available at https://www.iso.org/obp
-IEC Electropedia: available at http://www.electropedia.org/
3.1
saponification valuels
number of milligrams of potassium hydroxide required for the saponification of 1 g of the product tested
4Principle
The test sample is saponified by boiling under reflux with an excess of ethanolic potassium hydroxide,followed by ‘titration of the excess potassium hydroxide with standard volumetric hydrochloricacid solution.
5Reagents
Use only reagents of recognized analytical grade,and distilled or demineralized water ofequivalent purity.
5.1 Ethanol, volume fraction io = 95%.
5.2Potassium hydroxide, c(KOH) = o,5 mol/l solution in ethanol.
This solution shall be colourless or straw yellow. A stable colourless solution can be prepared by eitherof the following procedures.
a) Reflux 1 1 of ethanol (5.1) with 8 g of potassium hydroxide and 5 g of aluminium pellets for 1 h, then distil immediately. Dissolve the required amount of potassium hydroxide (approximately 35 g) inthe distillate. Allow to stand for several days, then decant the clear supernatant liquid from theprecipitated potassium carbonate into a brown-glass stock bottle.
b)Add 4 g of aluminium tert-butylate to 1 l of ethanol and allow the mixture to stand for several days. Decant the supernatant liquid and dissolve in it the required amount of potassium hydroxide.Allow to stand for several days, and then decant the clear supernatant liquid from the precipitatedpotassium carbonate into a brown-glass stock bottle.
5.3Hydrochloric acid, standard volumetric solution, c(HCl)J = 0,5 mol/1.
5.4Alkali blue 6B solution, p = 2,5g /100 ml in ethanol (5.1).
5.5 Phenolphthalein solution, p = 0,1 g/100 ml in ethanol (5.1).
Phenolphthalein is classified as CMR substance and should only be used when no alternative is available.5.6Boiling aids.
6 Apparatus
Usual laboratory apparatus and, in particular, the following.
6.1 Conical flask, of 250 ml capacity, made of alkali-resistant glass and having a ground neck.6.2Reflux condenser, with a ground glass joint that fits the conical flask (6.1).
6.3Heating device (e.g. a water-bath, electric hot-plate or other suitable apparatus). A naked flame isnot suitable.
6.4 Burette, capacity 50 ml, graduated in 0,1 ml divisions or automatic burette.
6.5 Pipette, capacity 25 ml or an automatic pipette.
6.6Analytical balance, readability o,000 1 g, weighing precision 0,001 g.
7 Sampling
Sampling is not part of this method specified in this document. A recommended sampling method isgiven in ISO 5555.
lt is important that the laboratory receive a truly representative sample that has not been damaged orchanged during transport or storage.
8Preparation of the test sample
Prepare the test sample in accordance with ISO 661.
The test samples are carefully mixed and filtered if visible impurities are present. If filtration is necessary, this shall be mentioned in the test report.
9 Procedure
9.1 Test portion Weigh, to the nearest 5 mg, approximately 2 g of the test sample (see Clause 8) into a conical flask (6.1). The test portion of 2 g has been determined on the basis of saponification values of 170 to 200. For other saponification values, the mass should be altered accordingly so that approximately half the ethanolic potassium hydroxide solution is neutralized. Recommendations for the mass of the test portion are given in Table 1.ISO 3657:2020 pdf download