This standard specifies the determination of freezing point in raw milk with thermistor cryoscope.
This standard is applicable to the determination of freezing point in raw milk.
2 Theory
Raw milk sample is cooled to moderate temperature; when the tested milk sample is cooled to -3℃, by releasing heat instantaneously, the sample crystallizes, then after the sample temperature achieves a balance and the temperature rising does not exceed 0.5℃ within 20s, the temperature is the freezing point of sample.
3 Reagents and Materials
Unless otherwise specified, reagents of analytically-pure or above and Grade II water (defined in GB/T 6682) are adopted for the purposes of this method.
3.1 Reagents
3.1.1 Ethylene glycol (C2H6O2).
3.1.2 Sodium chloride (NaCl).
3.2 Reagent preparation
3.2.1 Sodium chloride (NaCl): after being grinded, sodium chloride is placed in drying oven and dried at 130℃±2℃ for more than 24h, and then cooled to room temperature in dryer.
3.2.2 Coolant: measure 330mL of ethylene glycol (3.1.1), put it into a 1,000mL volumetric flask, then bring the volume with water to the scale and shake well; the volume fraction of the solution is 33%.
3.3 Sodium chloride standard solution
3.3.1 Standard solution A: weigh 6.731g of sodium chloride (3.2.1), dissolve it into 1,000g±0.1g of water. Store standard solution in polyethylene plastic bottles of 250mL or less separately and put the bottles in about 5℃ refrigerator for cold storage for a storage life of two months. The freezing point of the solution is -400m℃.
GB 5413.38-2016 The following standards are cited：
