GB/T 5527-2024Animal and vegetable fats and oils - Determination of refractive index (English PDF)

6.1.1 Refractometer. Refractive index measurement range. nD =

1.300 to nD = 1.700, refractive index readable to ±0.0001.

6.1.2 Light source. Sodium vapor lamp. If the refractometer is equipped with an achromatic compensation system, white light may also be used.

6.1.3 Glass plate. With known refractive index.

6.1.4 Circulating water bath device. With circulating pump and constant temperature control device, temperature control accuracy is ±0.1°C.

6.1.5 Constant temperature water bath. When the sample is solid, it can maintain the required temperature for measurement.

6.2 Sampling The samples received by the laboratory shall be representative, and shall not have been damaged or altered during transportation or storage. Sampling is not covered in this document; GB/T 5524 is recommended.

6.3 Sample Preparation Prepare the sample according to GB/T 15687.The sample used for refractive index measurement shall be a dried and filtered oil sample. For solid samples, prepare the sample according to GB/T 15687.Then, transfer it to a suitable container. Place it in a constant temperature water bath (6.1.5). The water bath temperature is set to the temperature at which the sample is to be measured. Leave it for sufficient time to allow the sample temperature to stabilize.

6.4 Operating Procedure

6.4.1 Instrument Calibration According to the operating procedures in the instrument manual, by measuring the refractive index of the glass plate (6.1.3) or measuring the refractive index of ethyl laurate (5.1), calibrate the refractometer (6.1.1).

6.4.2 Measurement

6.4.2.1 Measurement Conditions Select one of the following temperature conditions to measure the refractive index of the sample.

a) 20°C is applicable for oils that are completely liquid at this temperature;

b) 40°C is applicable for oils that do not completely melt at 20°C but completely melt at 40°C;

c) 50°C is applicable for oils that do not completely melt at 40°C but completely melt at 50°C;

d) 60°C is applicable for oils that do not completely melt at 50°C but completely melt at 60°C;

e) 80°C or above is used for other oils, such as fully hardened fats or waxes.

6.4.2.2 Measurement Procedure 6.4.2.2.1 Hot water from the water bath (6.1.4) is circulated through the refractometer to maintain the refractometer prism at the constant temperature t required for the measurement. 6.4.2.2.2 Use precision thermometer to measure the temperature of the water flowing out of the refractometer. Before measurement, lower the movable part of the prism to a horizontal position. Clean the prism surface first with a soft cloth, then with a cotton

6.6.2 Repeatability Within the same laboratory, by the same operator using the same equipment, following the same test method, the absolute difference between two independent test results obtained from testing the same object independently within a short period shall not exceed the repeatability limit (r) in Table A.1 for more than 5% of cases. If it must verify whether the repeatability requirement is met, two single-sample determinations shall be carried out according to the analysis steps in

6.6.3 Reproducibility In different laboratories, by different operators using different equipment, following the same test method, the absolute difference between two independent test results obtained from testing the same object independently shall not exceed the reproducibility limit (R) in Table A.1 for more than 5% of cases.

6.7 Test Report The test report must indicate. -- All relevant information required for the test sample; -- If the sampling method is known, indicate it; -- The test method adopted and the referenced standards; -- Any aspects not specifically described in this document, or deemed optional, as well as all operational details that may affect the results.

7.1 Instruments

7.1.1 Automatic refractometer. Refractive index measurement range is nD =

1.300 to nD = 1.700, and the refractive index is readable to ±0.0001.Built-in constant temperature controller. with selectable temperature control range of 20°C~99.9°C, and accuracy of 0.01°C.

7.1.2 Constant temperature water bath. When the sample is solid, it can maintain the temperature required for the measurement.

7.2 Sampling Same as 6.2.