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How does a refractometer work?

     Refractometers are optical instruments used to determine the percentage of soluble solids in a liquid solution. For this, the refractometer makes use of the principle of total refraction of light (originated by the type and concentration of dissolved substances in a liquid solution for example sugar), which takes place in the boundary layer between the prism and the sample. The refractive index of the prism determines the upper limit of the measurement range, since this must always be greater than that of the sample. The refractometer therefore measures the density of liquids, the more dense a liquid, the greater the refraction.

     densidad de liquidosIt is called refractometry, the optical method of determining the speed of light propagation in a medium / compound / substance / body, which is directly related to the density of this medium / compound / substance / body. To use this principle the refraction of light is used, (which is a fundamental physical property of any substance), and the scale of measurement of this principle is called refractive index, Refractometers are the instruments that use this principle of refraction either the refraction (using several prisms), or the critical angle, (using only one prism), and its primary scale of measurement is the refractive index, from which the different specific scales are constructed


     The refractometers were invented by Dr. Ernst Abbe, a German / Austrian scientist at the beginning of the 20th century. The Abbe refractometer is the "grandfather" of all modern refractometers, thanks to its simple operation and its reliability, it still has a place in laboratories. There are two types of refractometers based on the detection of the refractive index; transparent systems and reflection systems. Portable refractometers and Abbe refractometers use transparent systems, while digital refractometers use reflection systems.

How does a refractometer work?

Refractometer [YR01768]The refractometer is used to measure the refractive index of liquids and translucent solids allowing:

  • Identify a substance.
  • Verify its degree of purity.
  • Analyze the percentage of solute dissolved in a given solution.
  • Offer other qualitative analyzes.

      Its operation is based on using the refraction of light, which is a physical property of any substance and is related to some physical properties such as density. From this, and according to its application, different scales are built. The most commonly used scale is Brix Degrees (Proportion of sucrose or salts in a solution). There are other scales, such as: % salt, gs, g/dl, nD,% w / w,% vol,% water, mash sacch, M-10, MDT, among others.

 What are the parts of a refractometer?

  • Main Prism: It is where the samples are placed, it allows to measure different types of solutions, for example: drinks, sugar, honey, salt water, alcohol, jams, grapes, etc. The prism has a sheet that allows covering the substances that are deposited here.
  • Adjustment Screw: Used to adjust the calibration of the device.
  • Mirror Tube: Reflects light up through the refractometer.
  • Eyepiece: Focusable lens where the scale is observed.
  • Scale: Located inside, indicates the scale of measurement and varies according to its application and characteristics.

Measurement procedure

1. Place 1 or 2 drops of the sample on the prism

2. Close the sheet that prevents the entry of light, gently.

3. The sample should extend over the surface of the prism.

4. Look at the scale through the lens.

5. The reading of the scale is in frontier line.

6. Dry and clean the prism sample with tissue paper and water.

      Kalstein offers refractometers with high quality and high accuracy. That will help you determine with great accuracy the density of your solutions. That's why we invite you to take a look at our refractometers available HERE 

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This article was published on Tuesday 05 February, 2019.