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 Refractometer | Its types and its most important uses

Refractometer | Its types and its most important uses

? What is a refractometer

Refractometer is a device used the refractive index of the material to measure the specific density of liquids and the percentage of  dissolved solids .

The refractometer principle is based on the natural laws of refraction of light which is" when a ray of light passes from one place to another that differs from it in optical density, it has refraction at the separation surface and the amount of refraction indicates a constant value within a constant temperature and pressure " and we named it the refractive index which is
Refractive Index = sine of incidence / sine of angle of refraction

Types of Refractometers

Types of Refractometers

There are many types of refractometers , such as digital and manual, and in some types there are gradations that give the refractive factor only, and other types give the value of the refractive factor and the percentage of dissolved solids

An abbe refractometer

It is the most common type that gives readings of refractive index between 1.3000 - 1.7000 with an accuracy of 0.0001 and measures total soluble solids at concentrations of up to 95% .. it is associated with a separate sensor to place the sample and gives a direct reading of the concentration of brix, refractive index and temperature     

Refractometer Zeiss

It gives readings of refractive factor of 1.300 - 1.540 with an accuracy of 0.001 and measures total soluble solids from 0 - 95%.

Hand held refractometers

It is characterized by its light weight and accuracy of reading. It is used in the field or on production lines directly to measure the concentration of total dissolved solids .. There are types that give the concentration of total soluble solids from 0 to 30% .. And there are types from 30 - 75% according to the purpose for which it is used.

Characterization of the refractometer

  •  It is about glass prisms, one of them is fixed and the other is movable, between them the sample is placed
  • An eyepiece that sees inside a circle with two perpendicular lines in which the boundary between the illuminated and the dark area can be determined.
  • Horizontal scale is divided into two grades: the first gives the refractive factor of the sample and the second grading at the bottom gives the percentage of dissolved solids concentration
  • Light source
  • The device contains a moving water system to adjust the temperature around the prisms during measurement, and there is also a thermometer to measure the sample temperature

?How does the refractometer work

  • Clean the prisms with ethanol or isopropanol, then with water
  • Set the measurement temperature by passing a stream of water to the appropriate temperature through the two prisms
  • The reading is adjusted before using the refractometer by measuring the refractive factor of distilled water at a temperature of 20 ° C., as it should be 1.333
  • The sample is placed between the two prisms and must not contain suspended materials
  • The eyepiece is used to define the separating line between the illuminated area and the dark area, then we look at the gradation then we take the reading
  • The thermal adjustment is made to the reading if the measurement was at a temperature other than the standard temperature

: Note 

There is an inverse relationship between the refractive factor and temperature, and it is a basic factor that must be taken into account during the measurement process, for example, sugary and brine solutions are measured at a temperature of 20 ° C, oils are measured at a temperature of 40 ° C and fats at a degree of 60 ° C and when the measurement is at a different degree Standard degree thermal adjustment is made as follows

  • We add a number of 0.0001 to the value of the refractive factor for each degree Celsius greater than the ideal degree
  • We subtract a number of 0.0001 from the value of the measured refractive factor for each degree Celsius below the ideal degree

:Benefits of using refractometer

  • It is considered one of the preferred methods for estimating total dissolved solids or the refractive factor in samples due to its accuracy, speed and small quantities required for measurement as we need a few points
  • Determination of dissolved solids in sugary and brine solutions
  • Measuring the refractive factor of tomato juice and its products, in addition to measuring the percentage concentration of total solids
  • Determining the concentration of the solute in the solvent by comparing the refractive index of the solution gives us a standard
  • To know the degree of purity of the materials, i.e. the detection of adulteration, as each food item has a constant value of refractive factor at a certain temperature
  • It is important in the manufacture of margarine, as the refractive factor is used to adjust the amount of added hydrogen because the refractive factor increases with the increase in the iodine number
(Value used in the manufacture of margarine hydrogenated)

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