What are refractometers?
A refractometer is a piece of laboratory apparatus used for measuring the refractive index of gases, liquids, and translucent solids. Used for determining the chemical composition of substances, refractometers are commonly found in industrial and clinical laboratories.

How a Refractometer Works
When light enters a liquid it changes direction; this is called refraction. Refractometers measure the degree to which the light changes direction, called the angle of refraction. A refractometer takes the refraction angles and correlates them to refractive index (nD) values that have been established. Using these values, you can determine the concentrations of solutions. For example, solutions have different refractive indexes depending on their concentration in water.

The prism in the refractometer has a greater refractive index than the solution. Measurements are read at the point where the prism and solution meet. With a low concentration solution, the refractive index of the prism is much greater than that of the sample, creating a large refraction angle and a low reading (“A” on diagram). The reverse would happen with a high concentration solution (“B” on diagram).

The % Brix Scale
The % Brix Scale shows the concentration percentage of the soluble solids content of a sample (water solution). The soluble solids content is the total of all the solids dissolved in the water, beginning with sugar, salts, protein, acids, etc.; the measurement reading value is the value of the sum total of those. The Brix scale is calibrated to the number of grams of cane sugar contained in 100 g of water. When measuring a sugar solution, the % Brix reading should perfectly match the actual concentration.

Common Refractive Indexes
Refractive index readings are temperature-dependent.

Information Required to quote on a Benctop Refractometers

  1. What is your application?
  2. Do you require temperature compensation?
  3. What scale and range will you be measuring?
  4. What accuracy do you require?

Information Required to quote on a Handheld Refractometer

  1. What is your application?
  2. Do you require analogue or digital?
  3. Do you require temperature compensation?
  4. What scale and range will you be measuring?

Further Reading


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