BS EN 14108 Fat and oil derivatives - Fatty Acid Methyl Esters (FAME) - Determination of sodium content by atomic absorption spectrometry
5 Procedure
WARNING - In order to avoid polluting the sodium solutions, it is recommended to prepare all the determination solutions in polypropylene flasks and to conduct all the sampling operations using polypropylene pipettes or pipettes having disposable polypropylene tips. It is however possible to use glassware taking cleaning precautions in order to avoid pollution by the elements being analysed.
5.1 Sampling
Sampling is not part of the method spacified in this European Standard. A recommended sampling method is given in EN ISO 5555.
5.2 Preparation of the sample
5.2.1 Weigh to within 0.001 g approximately 2 g (mass m in g) of ester sample in a 50 ml volumetric flask (volume V in ml) and dilute to the mark with xylene.
5.2.2 Sample two test portions per sample.
5.3 Preparation of the set of calibration solutions
5.3.1 Prepare the calibrations solutions having the following sodium contents:
0.1 mg/l - 0.2 mg/l - 0.3 mg/l.
5.3.2 Using a variable volume automatic pipette, transfer 1.00 ml, 2.00 ml and 3.00 ml of the 5 mg/l sodium solution (3.6.2) into 50 ml volumetric flasks.
5.3.3 With a polypropylene pipette, add to each flask 10 ml of the 200 g/l solution of stock oil in xylene (3.4) and dilute to the mark with xylene.
5.3.4 Prepare the zero member or blank test in the same manner without adding any sodium solution.
5.3.5 Prepare the calibration solutions just prior to their measurement on account of their instability.
5.4 Spectrometric measurements
5.4.1 Preparation of the spectrometer
Set the wavelength at 589.0 nm and the band pass at 0.5 nm;
conduct the aspiration of the 0.3 mg/l calibration solution in order to optimize the different instrument settings. Seek the maximum response of the signal by adjusting:
- the air-acetylene gaseous mixture;
- the aspiration speed of the solution;
- the burner position.
conduct the aspiration of the xylene placed in a polypropylene bottle in order to set the instrument at zero absorbance.
5.4.2 Calibration
Conduct the aspiration of the blank (or zero member) and calibration solutions and carry out three measurements for each of them.
Calculate for each solution the arithmetical mean of the three measurements.
Plot the calibration curve from the means obtained.
By way of indication, the value of the optical density obtained for a 0.3 mg/l concentration is approximately 0.290 and the curve is more or less a straight line in the range considered.
5.4.3 Samples
Conduct the aspiration of the solutions of the samples and carry out the measurements in the same way as for the standards.
NOTE In the case where the measurement of the sample exceeds the set of calibration solutions given in 5.3, prepare standards having higher sodium contents, the maximum content being 1 mg/l.
