One, refraction method
Refraction is a method to identify the composition of the material by measuring the refractive index of the material, to determine the purity and concentration of the material and to determine the quality of the material.
The refractive index is one of the physical constants of material, it is the common indexes of process control in the production of food enterprises, when light from a transparent medium into a transparent medium will produce the phenomenon of refraction, usually in the determination of refractive index, are in the air as a comparison standard, namely the ratio of speed of light in the air and in a material speed, called the relative refractive index of this material, referred to as the refractive index. The refractive index, also called the refractive index and the index of refraction, is usually expressed in n.
Two, the relationship between the concentration of solution and the index of refraction
Homogeneous material has its intrinsic refractive index. For the solution of the same substance, the size of the refractive index is proportional to its concentration. Therefore, the purity and concentration of matter can be judged by measuring the refractive index of the material. Because refractive index is not affected by the viscosity and surface tension of the solution, it is very accurate to use the refraction method to determine the content of the substance.
For example, the oil is composed of fatty acid of certain fatty acids, each has its characteristics of refractive index, so the index of refraction of different oil, when the oil acidity increased, the refractive index will decrease when the relative density of oil increases, the refractive index increases, so the determination of oil index the rate can identify the composition and quality.
Three, the use of several common refractometer
The instrument used to determine the refractive index is a refractometer. The refractive index is usually characterized by the index of refraction, and some directly engraved with the mass fraction of the sugar solution. The commonly used refractometer in the food industry includes the handheld refractometer and the Abbey refractometer.
1. Handheld refractometer (Tang Liangji)
The handheld refractometer consists of three parts, that is, the eyepiece, the shading prism and the cover plate. When in use, first open the prism cover, with lens cleaning paper refraction prism is wiped clean, and then take a drop in sugar solution to be measured on the prism, close the cover, so that the solution uniformly coated on the surface of the prism, the light source window alignment, adjust the eyepiece diopter circle, the field of view in the field of clear vision, dark points the line is the corresponding log percentage of sugar solution.
The measuring range of the handheld refractometer is usually 0-90%. The standard temperature of the scale is 20. If it is measured at the non standard temperature, the temperature need to be corrected.
2. Abbe refractometer
The optical system of Abbey refractometer consists of two parts: an observation system and a reading system. The low calibration value of Abbe refractometer can be corrected at standard temperature. The refractive index is 1.33299. If correction temperature is not 20 degrees, correction is made.
Abbe refractometer with high scale value is usually part of a special standard glass with certain refractive index block correction, correction, put into the prism in the open, standard pieces of glass polishing on the surface with a bolb brominated naphthalene, and then the standard glass polishing side down, the glass block surface polishing stick in the birefringent prism on the surface, in order to receive the light, the measured refractive index of refraction should be consistent with the standard glass block mark rate correction if there is deviation of reading, to make reading instructions in the refraction of distilled water or standard glass block rate values, and then moving the instrument on the specific correction adjusting screw, the light the line just through the intersection of cross line.