BS/EN 17265-2019 pdf download.Foodstuffs – Determination of elements and their chemical species – Determination of aluminium by inductively coupled plasma optical emission spectometry (ICP-OES).
Further Instructions regarding test portions and digestion are given in B.2 and B.3.
For pressure digestion according to EN 13805, different vessels may be used depending on the instrument type and manufacturer. The maximum test portion and the minimum liquid volume depend on the pressure stability of the respective vessels. The specifications according to 7.1.2 refer to digestion vessels with volumes from 70 ml to 100 ml and a minimum liquid volume of 5 ml.
All indications in 7.1.2 shall be adjusted to the digestion instrument used. For safety reasons the manufacturer’s specifications shall be strictly followed.
7.1.2 Digestion procedure
Before digestion, different amounts of water, depending on the different types of food [31. are added in order to obtain comparable acid concentrations in the final digestion solution. The amount of water to be added depends on the test portion and thus on the content of carbon and water in the food type.
Add just as much water to the test portion that is necessary to suspend the food completely. Then complete the test portion with water to reach 3 g. Water is also added to fat-containing foods, even if a suspension is hardly possible.
Example for digestion of powdery food: Add 2,5 ml of water to the dry food, e.g. 0,5 g of flour. Mix the contents of the digestion vessel intensively, e.g. on a test-tube shaker. Repeat shaking every 10 mm to 15 mm until the suspension is homogeneous. No agglutinated particles shall remain, and the sample material shall be welled. Fat-containing samples require more time and repeated shaking. After at least 30 mm, add 2.5 ml of nitric acid (5.1) to the sample. Mix thoroughly again to obtain a homogeneous suspension. After the pre-reaction has subsided, close the digestion vessel, and start the digestion.
Example for digestion of a sample with high water content, e.g. lettuce: Directly add 2,5 ml of nitric acid (5.1) to 3 g of lettuce and mix thoroughly. It is not necessary to add water. After the pre-reaction has subsided, close the digestion vessel, and start the digestion.
A digestion temperature of at least 200 °C to be kept for at least 20 mm is required for a complete digestion in the microwave.
The digestion conditions depend on the manufacturers specifications, the reactivity of the sample, the maximum pressure stability of the digestion vessel, and the attainable temperature. To monitor the laboratory-specific digestion conditions, it is recommended to carry out measurements with reference materials containing certified contents [4j.
If precipitations or turbidities are visible in the digestion solutions, low findings can occur. In these cases, use smaller test portions and higher digestion temperatures up to 300 °C in order to minimize or avoid possible low findings.
NOTE Turbidities or small amounts of precipitates adhering to the wall or bottom of the vessel are only visible in vessels with high transparency (e.g. aluminium-free quartz vessels). Plastic vessels are often not completely transparent, making precipitates difficult to discern.
Fill up the digestion solution obtained by pressure digestion to a defined volume, e.g. 20 ml. Add the internal standard (5.4.3) (e.g. 1 000 jil) to an aliquot of the digestion solution, e.g. 5 ml, and fill up with water to 10 ml. Separate insoluble residues before measurement. If the digestion solution has a different final volume than 20 ml and a different dilution factor than 2 after addition of the internal standard, adapt the acid concentration of the calibration solutions respectively. All test solutions shall have approximately the same acid concentration as the calibration solutions. The digestion solution shall be measured within 2 weeks.
Matrix effects can occur in digestion solutions. It is recommended to dilute the digestion solution by a factor of 2 to reduce matrix effects and avoid contamination of Instruments.
In order to determine low aluminium contents reliably, choose a small filling-up volume after digestion. During sample preparation special care should be taken to avoid contaminations. See also explanation notes in Annex B.
7.2 Inductively coupled plasma optical emission spectrometry
7.2.1 ICP-OES operating conditions
Set the instrument according to the manufacturer’s specifications and ignite the plasma. After sufficient warming-up and stabilization of the instrument, optimize the settings.
7.2.2 Determination by ICP-OES
Once the instrument is optimized, start the measurement. For the determination of aluminium a wavelength of 396,15 nm is recommended. It is necessary to measure the emission intensity of the spectral background on both sides of the emission line and to subtract it from the intensity measured at a wavelength of 396,15 nm (spectral background correction on both sides).BS/EN 17265-2019 pdf download.
BS/EN 17265-2019 pdf download
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