BS EN ISO 20483:2013 pdf free

BS EN ISO 20483:2013 pdf free.Cereals and pulses一Determination of the nitrogen content and calculation of the crude protein content
Determine the moisture content, WH, of the test sample from an aliquot of the sample prepared according to Clause 8. Carry out the determination by following the method adapted to the product under test (i.e.ISO 712 for cereals and cereal products, ISO 6540 for maize, the method described in Reference[8] and which is used for testing certain pulses, or ISO 24557 for pulses).
If it is required to check that the requirements given concerning the repeatability limit (12.2) are fulfilled, carry out two separate determinations in accordance with 10.2 to 10.5.
Weigh, to the nearest 0,001 g, a mass of test sample prepared according to Clause 8, chosen on the basis of the assumed nitrogen content, so that the test portion contains between 0,005 g and 0,2 g of nitrogen and preferably more than 0,02 g.
WARNING – The following operations should be conducted under a well-ventilated, sulfuric acid-resistant hood.
Transfer the test portion (10.2) to the digestion flask. Then, add the required number of catalyst tablets (5.2), containing 10 g of potassium sulfate, 0,30 g of copper(II) sulfate pentahydrate and 0,30 g of titanium oxide. In the end, add 20 ml of sulfuric acid (5.3).
After a minimum of 2 h of digestion, counted from the time the unit temperature reached (420±10) °C again, leave to cool.
NOTE It is advisable to add pumice stone or glass boiling rods (5.11) as a boiling regulator and an antifoaming agent (5.4).
The minimum digestion time shall be checked on that reference material with which it was most difficult to reach the recovery rate (see 10.5).
Follow the recommendations of the equipment manufacturer as far as evacuation of the vapours is concerned, because too strong a suction can result in a loss of nitrogen.
Cautiously add to the cooled flask 50 ml of water and leave to cool. Transfer into the collecting flask 50 ml of boric acid (5.6) and, for visual colourimetry or using an optical probe, at least 10 drops of coloured indicator (5.72).
Add an excess of 5 ml of the sodium hydroxide solution (5.8) required for neutralizing the quantity of sulfuric acid used. Then carry out the distillation.BS EN ISO 20483 pdf download.