Principle and application of polarimetry

Polarimetry can be defined as the analysis of the rotation of polarized light by transparent components. Polarimetry is a sensitive and non-destructive technique for measuring the optical activity of organic and inorganic compounds. If linearly polarized light rotates as it passes, a compound is assumed to be optically active. The concentration of chiral molecules and the molecular composition of the material determine the amount of optical rotation. The direction and extent of rotation is useful for qualitative and quantitative analysis and is also useful for the elucidation of chemical composition. Optical behavior is the ability to polarize the rotation of light in the determination of certain compounds.


  1. What is a polarimeter?
  2. Principle of the polarimeter
  3. Principle of operation of the polarimeter
  4. polarimeter type
  5. Polarimeter Procedure
  6. Polarimeter applications
  7. Advantages of the polarimeter
  8. Disadvantages of the polarimeter
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Principle of the polarimeter:

The basic operating principle of a polarimeter includes a source that produces light with a specifically prepared linear polarization state, usually by passing through a polarizer. The light is transmitted by an optically active sample which often rotates the direction of polarization. After passing through the sample, another measurement of the angle of polarization modified by the light transfer by analysis, which can be rotated around the axis of the beam. The simplest technique is to move the analyzer to where optical power transmission is lowest.

Principle of operation of the polarimeter:

Polarimetry determines the rotation of polarized light as it travels through an optically active sample solution. A polarimeter includes a polarized light source, a filter, a sample cell, an analyzer, and a detector to measure the angle of rotation. The rotation determined can be used to measure the concentrations of samples, in particular sugar, vitamins, peptides and volatile oils.

Type of polarimeter:

Different types of polarimeters are mentioned below.

Manual polarimeter, fully automatic polarimeter, semi-automatic polarimeter, quartz wedge polarimeter, biquartz polarimeter, Lippich polarimeter and Laurent halftone polarimeter, etc.

Polarimeter procedure:

Before starting a polarimeter experiment, we need to recognize the different components needed to perform the process. Optical activity is calculated using polarimetry consisting of source, filter, sample cell, analyzer and detector.

Character font: Sodium vapor lamps are typically used to produce wavelengths above 450 nm.

Filtered: The nozzle is used to absorb unwanted radiation from polychromatic light into monochromatic light.

Sample cell: The sample cells are used to put the sample into the sample compartment, there it is made of glass and it has the shape of a long tube.

Analyzer: It is mainly used to analyze samples when they rotate on the right or left side of the plane of polarized light.

Detector: The photomultiplier tube is widely used for wavelength detection. The optically active component present in the solution causes the polarized light to rotate clockwise or counterclockwise. After that, the analysis calculates the twist angle and the detector detects it.

Polarimeter experimental procedure:

  • Prepare sample solutions and standard solutions as needed.
  • Turn on the instrument to start it and warm it up for about 5 minutes.
  • Spin the Polaroid wheel until the screen displays "ZERO".
  • Place the polarimeter tube inside the instrument and close the lid.
  • Roll the wheel back and forth to display minimum intensity. Note the degree readings (X1) and do not disturb the system.
  • Then remove the tube and fill it with the solution to be tested and put it back in place. The sample intensity will increase due to the rotation of the plane of polarization.
  • Turn the wheel in the direction of decreasing intensity until the intensity reaches the minimums and note the readings in degrees (X2).

Polarimeter Applications:

  • Polarimetry is used to determine specific rotation and optical rotation of products such as amino acids, cocaine, antibiotics, dextrose, carbohydrates, analgesics, vitamins, steroids, sugars, serums, diuretics , codeine, etc.
  • For its structural determination, it can be used. In this application, optical rotation changes are estimated based on the chemical change of the substance.
  • It is used to assure product quality by determining the purity and concentration of compounds in sugar foods, syrups and cereals.
  • Polarimeter applications consist of the quantitative and qualitative analysis of optically active components.
  • Polarimetry is used in the analysis of manufacturers of perfumes, aromas and essential oils
  • Chiral compounds can also be determined by polarimetry.

Advantages of the polarimeter:

  • Polarimetry is an easy-to-use technique and does not require experts to operate.
  • It is not affected by changes in laser intensity.
  • The temperature and pH inside the eye remain stable.
  • The advanced version of the polarimeter has a wide range of emission wavelengths compared to conventional light sources.
  • The analysis is very easy and fast, which means it is a profitable technique.

Disadvantages of the polarimeter:

  • To determine the specific and optical rotation of a substance, large sample volumes with high concentrations were required.
  • The main disadvantage of polarimetry is that only optically active components can be analyzed by polarimetry.
  • It has a low sensitivity compared to other techniques.
  • It is very sensitive to movement and dispersion.

The most frequently asked questions about the polarimeter are as follows.

What is the polarimeter?

A polarimeter is an analytical tool used to determine the angle of rotation due to the passage of polarized light through the optically active molecule.

How does a polarimeter measure optical rotation?

A polarimeter is a tool that determines the angle of rotation without passing the polarized light source through the optically active material.

What light source is used in the polarimeter?

The sodium (Na) vapor lamp is used in a polarimeter as a light source because it produces high-energy monochromatic light.

What is the main advantage of a polarimeter?

The main advantage of a polarimeter is its analysis of a wide range of compounds.

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