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ISO 8986-1-2014 pdf free download
ISO 8986-1-2014 pdf free download.Milk and milk products Determination of nitrogen content
Part 1:Kjeldahl principle and crude protein calculation
Lait et produits laitiers — Determination de la teneur en azote — Partie 1: Méthode Kjeldahl et calcul de Ia teneur en protéines brutes.
a) the tablets contain a quantity of potassium sulfate such that the required amount can be dispensed using an integer number of whole tablets to maintain a similar salt to acid (5) ratio. For instance, three tablets each containing 5 g of potassium sulfate, may be used with 20 nil of sulfuric acid (53), and
b) the tablets do not contain salts of toxic metals, such as selenium or mercury.
Turn on the fume extraction system of the digestion apparatus (6110) prior to beginning the digestion. Heat the digestion flask and its contents (9J.J.) on the digestion apparatus using a heater setting low enough such that charred digest does not foam up the neck of the digestion flask. Digest at this heat setting until white fumes appear in the flask after approximately 20 mm. Increase the heater setting to half way to the maximum setting determined in 1L and continue the heating period for 15 mm. At the end of the 15-mm period increase the heat to maximum setting determined in fLifi. After the digest clears (clear with light blue-green colour), continue boiling for 1 h to 2,5 h at maximum setting. If visible boiling of the clear liquid is not apparent as bubbles forming at the surface of the hot liquid, the temperature of the heating device might be too low. The total digestion time will be between 1,8 h and 3,25 h.
To determine the specific boiling time required for analysis conditions in a particular laboratory using a particular set of apparatus, select for milk analysis a high-protein, high-fat milk sample and determine its protein content using different boiling times (1 h to 2,5 h) after clearing. Other milk products require samples of compositions similar to those being tested. The mean protein result increases with increasing boil time, becomes constant and then decreases when boil time is too long, Select the boil time that yields the maximum protein result for the product tested.
At the end of digestion. the digest shall be clear and free of undigested material. Allow the digest to cool to room temperature In an open flask in a separate hood over a period of approximately 25 mm. If the flask Is left on the hot heating device to cool, It will take longer to reach room temperature. The cooled digest should be liquid or liquid with a few small crystals at the bottom of the flask at the end of the 25- mm cooling period. Do not leave the undiluted digest in the flasks overnight. The undiluted digest might crystallize during this period and it will be very difficult to get the crystallized digest back into solution.
NOTE Excessive crystallization after 25 mm is the result of undue acid loss during digestion and can result In low test values. Undue acid loss Is caused by excessive fume aspiration or by an excessively long digestion time caused by an incorrect maximum burner setting.
Add 300 ml of water to the 500 ml digestion flasks or 400 ml of water when using the 800 ml digestion flasks. Wash down the neck of the flask during the addition of water. Mix the contents thoroughly ensuring that any crystals that separate out are dissolved.ISO 8986-1-2014 pdf free download.
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