BS EN ISO 1736:2000 pdf – Dried milk and dried milk products Ð Determination offat content Ð Gravimetric method (Reference method).
5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or water of equivalent purity. The reagents shall leave no appreciable residue when the determination is carried out by the method specified (see 9.2.2). 5.1 Ammonia solution, containing a mass fraction of NH 3 of approximately 25 % (? 20 = 91 0 g/l). NOTE? If ammonia solution of this concentration is not available, a more concentrated solution of known concentration may be used (see 9.4.2). 5.2? Ethanol (C 2 H 5 OH), or ethanol denatured by methanol, containing a volume fraction of ethanol of at least 94 %. (See A.5.) 5.3? Congo red solution Dissolve 1 g of Congo red in water in a 1 00 ml one-mark volumetric flask (6.1 4). Dilute to the mark with water. NOTE? The use of this solution, which allows the interface between the solvent and aqueous layers to be seen more clearly, is optional (see 9.4.4). Other aqueous colour solutions may be used provided that they do not affect the result of the determination. 5.4? Diethyl ether (C 2 H 5 OC 2 H 5 ), free from peroxides (see A.3), containing no more than 2 mg/kg of antioxidants, and complying with the requirements for the blank test (see 9.2.2, A.1 and A.4). NOTE? The use of diethyl ether could lead to hazardous situations. Due to expected changes in safety regulations, studies are ongoing to replace diethyl ether by another reagent provided that it does not affect the end result of the determination. 5.5? Light petroleum, with any boiling range between 30 °C and 60 °C or, as equivalent, pentane (CH 3 [CH 2 ] 3 CH 3 ) with a boiling point of 36 °C and complying with the requirements for the blank test (see 9.2.2, A.1 and A.4). NOTE? The use of pentane is recommended because of its higher purity and constant quality. 5.6? Mixed solvent Shortly before use, mix equal volumes of diethyl ether (5.4) and light petroleum (5.5).
6.4? Drying oven, electrically heated, with ventilation port(s) fully open, capable of being maintained at a temperature of 1 02 °C ? 2 °C throughout its working space. The oven shall be fitted with a suitable thermometer. 6.5? Water bath, capable of being maintained at a temperature of 65 °C ? 5 °C. 6.6? Mojonnier-type fat-extraction flasks, as specified in ISO 3889. NOTE? It is also possible to use fat-extraction tubes, with siphon or wash-bottle fittings, but then the procedure is different. The alternative procedure is given in annex B. The fat-extraction flasks shall be provided with good quality corks or stoppers of another material [e.g. silicone rubber or polytetrafluoroethylene (PTFE)] unaffected by the reagents used. Bark corks shall be extracted with the diethyl ether (5.4), kept in water at a temperature of 60 °C or more for at least 1 5 min, and shall then be allowed to cool in the water so that they are saturated when used. 6.7? Rack, for holding the fat-extraction flasks (or tubes) (6.6). 6.8? Wash bottle, suitable for use with the mixed solvent (5.6). A plastics wash bottle shall not be used. 6.9? Fat-collecting vessels, such as boiling flasks (flat-bottomed), of capacities 1 25 ml to 250 ml, conical flasks, of capacity 250 ml, or metal dishes. If metal dishes are used, they shall be of stainless steel, flat-bottomed with a diameter of 80 mm to 1 00 mm and a height of approximately 50 mm. 6.10 Boiling aids, fat-free, of non-porous porcelain or silicon carbide (optional when metal dishes are used). 6.11 Measuring cylinders, of capacities 5 ml and 25 ml. 6.12 Pipettes, graduated, of capacity 1 0 ml. 6.13 Tongs, made of metal, for holding flasks, beakers or dishes. 6.14 Volumetric flask, one-mark, of capacity 1 00 ml.
9.1? Test portion Mix the test sample (clause 8) by gently stirring or rotating and inverting the container several times. Immediately weigh to the nearest 1 mg, directly or by difference, in a fat-extraction flask (6.6) one of the following test portions: a)? about 1 g of dried high-fat milk, of dried whole milk or of dried butter serum; b)? about 1 ,5 g of dried partially skimmed milk; c)? about 1 ,5 g of dried skimmed milk; d)? about 1 ,5 g of dried whey; e)? about 1 ,5 g of dried buttermilk. Transfer the test portion as completely as possible into the lower (small) bulb of the fat-extraction flask. 9.2? Blank tests 9.2.1? Blank test for method Carry out a blank test simultaneously with the determination using the same procedure and same reagents, but replacing the dispersed test portion in 9.4.1 by 1 0 ml of water (see A.2). If the value obtained in the blank test regularly exceeds 1 ,0 mg, check the reagents if this has not been recently done (9.2.2). Corrections of more than 2,5 mg should be mentioned in the test report. 9.2.2? Blank test for reagents To test the quality of the reagents, carry out a blank test as specified in 9.2.1 . Additionally use an empty fat- collecting vessel, prepared as specified in 9.3, for mass control purposes. The reagents shall leave no residue greater than 1 ,0 mg (see A.1 ).