BS EN 14112 Fat and oil derivatives - Fatty Acid Methyl Esters (FAME) - Determination of oxidation stability (accelerated oxidation test)
6 Sampling
It is important that the laboratory receive a sample which is truly representative and has not been damaged or changed during transport and storage.
Sampling is not part of the method specified in this European Standard. A recommended sampling method is given in EN ISO 5555.
Store the sample in the dark at about 4 °C.
7 Preparation of measurement
7.1 Preparation of test sample
In order to prevent the preparation of the test sample from influencing the test result, all handling of the laboratory sample shall be restricted to the steps given below.
Remove the required quantity from the centre of the carefully homogenised sample using a pipette.
NOTE Samples should be analysed immediately after the test sample preparation.
7.2 Preparation of apparatus
7.2.1 Cleaning procedure
Wash the reaction vessels, measurement cells and their inlet and outlet tubes at least three times with acetone in order to remove as much of the organic residue as possible. Rinse with tap water.
Fill the vessels completely with an aqueous alkaline laboratory glass cleaning solution and mount the inlet tubes. Store the vessels at least 2 h at 70 °C.
Rinse the purified vessels and their inlet and outlet tubes thoroughly with tap water and finally with demineralized or distilled water. Dry them in an oven for at least 1 h at 110 °C.
NOTE 1 If there are disposable reaction vessels available, the described cleaning procedure for these is not necessary.
NOTE 2 Check of the cleanliness of vessels: run clean vessels using distilled water for six hours in the same experimental conditions in order to check if the measured conductivity shows any significant change during time. Vessels showing conductivity changes should be discarded and cleaned again. The vessels passing the test can be used after water removal and drying in oven.
7.2.2 Determination of temperature correction
The difference between the actual temperature of the sample and the temperature of the heating block is called temperature correction ΔT. For the determination of ΔT an external calibrated temperature sensor is used.
Before starting the determination of ΔT the heating block has to be switched on and the target temperature has to be reached.
Fill one reaction vessel with 5 g thermostable oil. Insert the temperature sensor through the cap into the reaction vessel. Use distance clips to keep the sensor away from the air inlet. The sensor should touch the bottom of the vessel.
Insert the complete vessel into the heating block and connect the air supply.
If the value of the measured temperature is constant, calculate ΔT:
sensor Block
ΔT = TBlock - Tsensor
ΔT is the delta T "temperature correction";
TBlock is the temperature of the heating block;
Tsensor is the measured temperature in the reaction vessel.
Correct the block temperature:
TBlock = TTarget + ΔT
After this temperature correction the measured temperature in the reaction vessel should be equal to the target temperature.
