ANNEX IIU.K. [F1DETERMINATION OF FREE FATTY ACIDS, COLD METHOD]
Textual Amendments
1.DETERMINATION OF ACIDITYU.K.
The determination of free fatty acids in olive oils. The content of free fatty acids is expressed as acidity calculated conventionally.
1.1.PrincipleU.K.
A sample is dissolved in a mixture of solvents and the free fatty acids present titrated using an ethanolic solution of potassium hydroxide.
1.2.ReagentsU.K.
All the reagents should be of recognized analytical quality and the water used either distilled or of equivalent purity.
1.2.1. [X1Diethyl ether]; 95 % ethanol (v/v), mixture of equal parts by volume.U.K.
Note:U.K.
[X1Diethyl ether] is highly inflammable and may form explosive peroxides. Special care should be taken in its use.U.K.
Neutralize precisely at the moment of use with the potassium hydroxide solution (1.2.2), with the addition of 0,3 ml of the phenolpthalein solution (1.2.3) per 100 ml of mixture.
Note:U.K.
If it is not possible to use [X1diethyl ether], a mixture of solvents containing ethanol and toluene may be used. If necessary, ethanol may be replaced by propanol-2.U.K.
1.2.2.Potassium hydroxide, titrated ethanolic solution, c(KOH) about 0,1 mol/l or, if necessary, c(KOH) about 0,5 mol/l.U.K.
The exact concentration of the ethanolic solution of potassium hydroxide must be known and checked immediately prior to use. Use a solution prepared at least five days before use and decanted into a brown glass bottle with a rubber stopper. The solution should be colourless or straw coloured.
Note:U.K.
A stable colourless solution of potassium hydroxide may be prepared as follows. Bring to the boil 1 000 ml of ethanol with 8 g of potassium hydroxide and 0,5 g of aluminium shavings and continue boiling under reflux for one hour. Distill immediately. Dissolve in the distillate the required quantity of potassium hydroxide. Leave for several days and decant the clear supernatant liquid from the precipitate of potassium carbonate.U.K.
The solution may also be prepared without distillation as follows: to 1 000 ml of ethanol add 4 ml of aluminium butylate and leave the mixture for several days. Decant the supernatant liquid and dissolve the required quantity of potassium hydroxide. The solution is ready for use.
1.2.3.Phenolphthalein, 10 g/l solution in 95 to 96 % ethanol (v/v) or alkaline blue, (in the case of strongly coloured fats) 20 g/l solution in 95 to 96 % ethanol (v/v).U.K.
1.3.ApparatusU.K.
Usual laboratory equipment including:
1.3.1.analytical balance;U.K.
1.3.2.250 ml conical flask;U.K.
1.3.3.10 ml burette, graduated in 0,05 ml.U.K.
1.4.ProcedureU.K.
1.4.1.Preparation of the specimen for testingU.K.
(Carry out the test on the filtered sample. Where moisture and impurities together are less than 1 %, use the specimen without further treatment; where they exceed 1 %, it should be filtered.)
1.4.2.Taking the sampleU.K.
Take a sample depending on the presumed acid number in accordance with the following table:
| Expected acid value | Mass of sample(g) | Weighing accuracy(g) |
|---|---|---|
| < 1 | 20 | 0,05 |
| 1 to 4 | 10 | 0,02 |
| 4 to 15 | 2,5 | 0,01 |
| 15 to 75 | 0,5 | 0,001 |
| > 75 | 0,1 | 0,0002 |
Weigh the sample in the conical flask (1.3.2).
1.4.3.DeterminationU.K.
Dissolve the sample (1.4.2) in 50 to 150 ml of the previously neutralized mixture of diethyl [X1ether] and ethanol (1.2.1).
Titrate while stirring with the 0,1 mol/l solution of potassium hydroxide (1.2.2) (see Note 2) until the indicator changes (the pink colour of the phenolphtalein persists for at least 10 seconds).
Note 1.U.K.
The titrated ethanolic solution of potassium hydroxide (1.2.2) may be replaced by an aqueous solution of potassium or sodium hydroxide provided that the volume of water introduced does not induce phase separation.U.K.
Note 2.U.K.
If the quantity of 0,1 mol/l potassium hydroxide solution required exceeds 10 ml, use the 0,5 mol/l solution.U.K.
Note 3.U.K.
If the solution becomes cloudy during titration, add enough of the solvents (1.2.1) to give a clear solution.U.K.
1.5.Acidity: expressed as percentage of oleic acidU.K.
Acidity as a percentage by weight is equal to:
where:
=
the volume of titrated potassium hydroxide solution used, in millilitres;
=
the exact concentration in moles per litre of the titrated solution of potassium hydroxide used;
=
the molar weight in grams per mole of the acid used to express the result (= 282);
=
the weight in grams of the sample.
[X1Take as the result, the arithmetic mean [F2of two calculations] carried out.]