BS EN ISO 8968-1:2014 pdf free

BS EN ISO 8968-1:2014 pdf free.Milk and milk products一Determination of nitrogen content
Turn on the fume extraction system of the digestion apparatus (6.10) prior to beginning the digestion.Heat the digestion flask and its contents (9.1.1) 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 min. Increase the heater setting to half way to the maximum setting determined in 6.10 and continue the heating period for 15 min.At the end of the 15-min period increase the heat to maximum setting determined in 6.10. 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 biling 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 min. 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-min 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 min 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.BS EN ISO 8968-1 pdf download.