EN 14104 Fat and oil derivatives - Fatty Acid Methyl Esters (FAME) - Determination of acid value
5 Reagents
Use only reagents of recognised analytical grade and water of grade 3 in accordance with EN ISO 3696.

5.1 Diethyl ether and 95 % ethanol, 1 + 1 mixture by volume.

WARNING Diethyl ether is very flammable and may form explosive peroxides. Use with great caution.

Neutralise, just before use, by adding the potassium hydroxide solution (5.2) in the presence of 0.3 ml of phenolphthalein alcoholic solution (5.3) per 100 ml of solvent mixture.

If it is not possible to use diethyl ether, a mixed solvent may be used as follows:
toluene and 95 % (V/V) ethanol, 1 + 1 mixture by volume;
toluene and 99 % (V/V) 2-propanol, 1 + 1 mixture by volume.
The mixed solvent can be replaced by 99 % (V/V) 2 propanol.

NOTE Larger volumes of solvent mixture and indicator may be necessary for dark-coloured samples.

5.2 Potassium hydroxide, standard volumetric solution in ethanol:
c(KOH) = 0.1 mol/l

The ethanolic potassium hydroxide solution can be replaced by aqueous potassium or sodium hydroxide solutions, but only if the volume of water introduced does not lead to phase separation.

5.2.1 Preparation of the solution
Dissolve approximately 7 g of potassium hydroxide pellets in ethanol and dilute to 1000 ml with the same solvent.

NOTE 2 propanol can be used instead of ethanol.

Weigh, to the nearest 0.0002 g, 0.15 g of benzoic acid having minimum purity 99.9 % (m/m), or another primary standard, in a 150 ml beaker and dissolve in 50 ml of 4-methylpentan-2-one (5.4). Use a pH meter to follow titration and to detect the end point, start the stirrer and titrate with the potassium hydroxide solution to the equivalence point.

5.2.2 Calculation of the solution concentration
The concentration of the potassium hydroxide solution, expressed in moles per litre, (when benzoic acid is used), is given by:
(1000 x m0)/(122.1 x V0)
where
m0 is the mass, reported in grams, of benzoic acid used;
V0 is the volume, in millilitres, of potassium hydroxide solution used to reach the endpoint.

NOTE 1 In the above and later mathematical expressions, the symbol represents the numerical values of the quantities.

NOTE 2 Potassium hydroxide standardised solutions are commercially available and suitable for use.

Use solution prepared at least 5 days previously and decanted into a brown glass bottle, fitted with a rubber stopper provided with a thermometer needed for temperature correction (see 10). The solution shall be colourless or straw yellow. If the bottle is connected to the burette, provision shall be made to prevent intake of carbon dioxide, for example by using a tube filled with granular soda lime.

5.3 Phenolphthalein, 10 g/l solution in 95 % Ethanol.

5.4 4-Methylpentan-2-one neutralized just before use by adding the potassium hydroxide solution (5.2) using the pH-meter (6.3).

6 Apparatus
Usual laboratory equipment and, in particular:
6.1 Microburette, 10 ml capacity, graduated in 0.02 ml subdivisions.

6.2 Analytical balance, capable of weighing with an accuracy of +/- 0.05 g or less.

6.3 pH-meter, equipped with glass and calomel electrodes.

7 Sampling
Sampling is not part of the method specified in this European Standard. A recommended sampling method is given in EN ISO 5555.

It is important that a laboratory receives a sample, which is truly representative and has not been damaged or changed during transportation and storage.

8 Preparation of test sample
Prepare the test sample in accordance with EN ISO 661. The test sample shall not be heated and/or filtered.