BS ISO 6732:2010 pdf download – Milk and milk products — Determination of iron content — Spectrometric method (Reference method)
5.1 Analytical balance.
5.2 Centrifuge, capable of producing a radial acceleration of 2 500g, with tubes of capacity at least 150 ml.
5.3 Grinding device, appropriate to the nature of the sample.
5.4 Sieve, nominal size of openings 500 µm, ISO 565 [1] , made of iron-free material.
5.5 Water baths.
5.6 Micro-burners or electric heaters, which do not emit iron-containing particles.
5.7 Digestion flasks (Kjeldahl), capacity approximately 70 ml, with ground-glass stoppers, calibrated on the lower part of the neck at 50 ml.
5.8 Glass beads, preferably made of quartz, which do not release iron during the digestion procedure (see 8.2.1).
5.9 Measuring cylinders, capacities 5 ml, 10 ml and 25 ml, ISO 4788 [6] .
5.10 Graduated pipettes, capacities 1 ml, 2 ml and 5 ml, graduated in divisions of 0,1 ml, ISO 835 [4] .
5.11 One-mark pipettes, capacities 1 ml, 2 ml, 3 ml, 4 ml, 5 ml, 10 ml and 25 ml, ISO 648 [2] class A.
5.12 Spectrometer, suitable for measuring absorbance at 533 nm, equipped with cells of optical pathlength 10 mm.
6 Sampling
IMPORTANT — Avoid contamination by iron. Store glass sampling jars in 10 % mass fraction nitric acid solution. Rinse them thoroughly and dry before use.
Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 707|IDF 50 [3] .
It is important that the laboratory receive a truly representative sample which has not been damaged or changed during transport or storage 7 Preparation of test sample
IMPORTANT — Avoid contamination by iron.
7.1 Milk,skimmed milk and whey
Bring the sample to (20±2)°C and mix carefully. lf, in the case of milk, the fat is not evenly dispersed, heatthe sample slowly to 40 °℃, mix gently by inversion only, and cool quickly to (20 ±2)°℃.
lf necessary, remove butter granules. Bring the sample to (20±2)C and mix carefuy, immediately beforeweighing (see 8.1.1).
7.3 Plain yogurt and skimmed yogurt
Bring the sample to (20±2) ℃ and mix carefully. lf serum separates, stir vigorously,immediately beforeweighing (see 8.1.1).
Bring the sample to (20±2) °℃.Mix or stir thoroughly, but not so vigorously as to cause frothing or churning.lf the cream is very thick, or if the fat is not evenly dispersed, warm slowly to 40 °C to facilitate mixing.
Cool the sample quickly to (20±2) °℃. Stir the sample in the container thoroughly.Mix until the whole mass ishomogeneous.Close the container.
Correct results cannot be expected if adequate mixing of the sample is not achieved or if the sample showsany evidence of churning or any other signs of abnormality.
7.5Evaporated milk
Shake the container thoroughly,inverting it frequently.Open the container and pour the milk slowly intoanother container made of glass, provided with an airtight lid, taking care to incorporate in the sample any fator other constituents adhering to the wall of the original container. Stir vigorously and close the container.
Heat the closed container in a water bath at 40 °C to 60 °C.Remove and shake the container vigorously every15 min. After 2 h, remove the container and cool to (20±2)°℃.Remove the lid and mix thoroughly by stirringthe sample with a spoon or spatula.
lf the fat separates,correct results cannot be expected.7.6Sweetened condensed milk
Open the container and thoroughly mix the mlk with a spoon or spatula,using an up-and-down rotarymovement in such a way that the top and bottom layers are moved and mixed.Take care to incorporate in thesample any milk adhering to the wall and ends of the container.
Transfer the sample as completely as possible to a second container made of glass, provided with an airtightlid, and close this container.Heat the closed container in a water bath at 30 °C to 40 °℃.Cool to (20±2)c.Stir the sample in the container thoroughly. Mix until the whole mass is homogeneous.Close the container.
In the case of a collapsible tube, open it and transfer the contents to a glass container. Cut open the tube andtransfer as completely as possible all material adhering to the interior of the container.