Automatic refractometer Digipol-R300 oil detection scheme

I. Introduction

When light propagates between different substances, the ratio of the incidence Angle sine to the Angle of refraction sine, the refractive index, is an inherent property of matter. Different substances have a specific refractive index, and for a solution, its concentration is closely related to the refractive index, usually in a positive relationship. In the field of oils and fats, this property is of great significance. Natural oils are mixtures of mixed glycerides, and different sources of oils have different refractive indices due to differences in the composition of glycerides, which become the unique "fingerprint" of each oil. Moreover, once the quality of the oil changes, such as doping, rancidity, etc., its refractive index will also change accordingly. For example, oils with high relative density have a higher refractive index; When the acidity of oil increases and the density decreases, the refractive index will decrease. Therefore, the accurate measurement of the refractive index of oil becomes the key means to identify the type, judge the purity and evaluate the quality of oil.

2. Experiment preparation
2.1 Test equipment

The Digipol-R300 fully automatic refractometer from Shanghai Jiahang combines advanced optical systems, high-precision temperature control modules and intelligent data processing technology to ensure measurement accuracy and stability. The optical system adopts high-quality optical components, which can accurately capture the Angle of light refraction. Temperature control module can realize accurate temperature control and reduce the influence of temperature on measurement results. The intelligent data processing system can process and display the measurement data quickly.

2.2 Experimental reagents
Soybean oil (CASA # 8001-22-7) : a common edible vegetable oil, widely used in food processing and other fields.
Peanut oil (CASA # 8002-03-7) : has a unique flavor and is widely used in cooking and food preparation.
Corn oil (CAS# 8001-30-7) : Rich in nutrients, it is a common edible oil variety.
2.3 Reference Standards
"Animal and vegetable oil refraction index determination GB/T 5527-2010". The standard specifies in detail the determination method, equipment, operation procedure and result expression of animal and vegetable oil refractive index, which provides the authoritative operation specification and judgment basis for this experiment.

3. Sample testing
Instrument startup preheating and temperature setting: connect Digipol-R300 automatic refraction instrument power supply, startup preheating. The preheating time is based on the instructions of the instrument to ensure that the instrument reaches a stable working state. After the preheating, set the prism temperature to 20℃ on the instrument operating interface. The instrument uses efficient temperature control technology to quickly and accurately stabilize the prism temperature at the set value, providing a stable environment for accurate measurement.
Sample drip and shading treatment: Use a clean dropper to absorb an appropriate amount of the grease sample to be measured, and slowly and evenly drop it onto the surface of the instrument prism to ensure that the sample is completely covered with the prism surface to avoid bubbles or uneven distribution of the sample. After the drip is completed, the mask is quickly covered to prevent external light from interfering with the measurement process and ensure the accuracy of the measurement results.
Measurement and data reading: After the temperature between the sample and the prism surface reaches a balance (which can be judged by the built-in temperature sensor and balance indicator identifier of the instrument), click the "Measure" button on the instrument operation interface to measure. Click the measurement button continuously and closely observe the change of refractive index value on the instrument display. When the value is stable, usually the fourth decimal place no longer changes, the measurement result is regarded as stable, and the refractive index value is recorded at this time.
Prism cleaning and parallel testing: After the measurement is complete, carefully wipe the sample residue from the prism surface. Use a solvent that can dissolve the sample, such as alcohol, petroleum ether, etc., to carefully clean the prism surface to ensure that there is no residual sample on the prism surface. After cleaning, rinse with distilled water and dry with a clean soft cloth. Follow steps 2 and 3 above to perform at least three parallel tests on the same grease sample, ensuring that the instrument is in good condition and the prism is clean before each test. The average of the three measurements is calculated as the refractive index measurement of the sample.
4. Results and discussion
4.1 Test Interface
The Digipol-R300 fully automatic refractometer features an intuitive and convenient test interface. On the main interface, the current set temperature, the sample temperature, the real-time index of refraction (nD) value in the measurement, and the corresponding Brix value (if the instrument has the measurement capability) are displayed in real time. At the same time, the interface also clearly marked the measurement wavelength, reference temperature and other key information. During the measurement process, the operator can view the measurement status prompt at any time, such as "Measurement, please wait". There are function buttons such as "Measurement", "Measurement record", "Report" and "Setting" on the interface, which are convenient for users to carry out various operations. By clicking "Measurement Record" button, you can view the historical measurement data; The "Report" button is used to generate and print measurement reports; The "Set" button can adjust the temperature, measurement mode and other parameters of the instrument.

4.2 Experimental Results

As a key index of edible oil quality, refractive index is closely related to the composition of fatty acids. In general, the greater the molecular weight of the fatty acid and the higher the unsaturation, the greater the refractive index. For example, oils containing more short-chain saturated fatty acid esters have a relatively low refractive index; Oils rich in unsaturated acids, such as linseed oil, have a higher refractive index. In practical application, refractive index measurement plays an important role in quality control and quality inspection of edible oil. On the one hand, it can be used as an effective means to quickly detect fake and inferior products. If a certain oil claims to be a specific variety, its refractive index differs greatly from the standard refractive index of that variety of oil, it is likely to be adulterated or counterfeit. On the other hand, the change of physicochemical indexes in the aging process can be studied by measuring the refractive index of long-stored oils. Experimental studies have shown that the refractive index of common vegetable oils usually increases significantly after aging. Therefore, the determination of the refractive index of oil is simple, rapid, safe and reliable, and can be used as an important auxiliary method to determine whether the oil is rancidity and aging.

4.4 Digipol-R300 automatic refractometer instrument parameters