Polarimetry: determination of chirality and optical purity of substances
Analyze the optical composition of your substances using polarimetry
Polarimetry is an analytical technique for measuring the angle of rotation of polarized light as it passes through a chiral substance. It is primarily used to determine the optical purity, concentration, and identity of optically active compounds and plays a key role in the pharmaceutical, food, and chemical industries .
Thanks to its precision and non-destructive nature, polarimetry is a method of choice for quality control and compliance with regulatory standards.
How does polarimetry work?
Polarimetry is based on the interaction between polarized light and a chiral substance. Its principle is based on the following steps :
- Polarized light beam emission – A light source (usually a laser or sodium lamp) sends polarized light through the sample.
- Interaction with chiral substance – If the solution contains optically active molecules, they will rotate the plane of polarization of light.
- Rotation angle measurement – An analyzer detects the rotation angle of the output light and compares it to the initial value.
- Interpretation of results – The measured angle allows the concentration and optical purity of the compound to be determined according to Biot's law.
The rotation angle depends on several parameters: the wavelength of the light used, the concentration of the substance, the temperature and the length of the measuring tube.
Technical characteristics of polarimetry
Polarimetry to various analytical conditions:
- Wavelength range : often centered around 589 nm (sodium lamp) or other sources in the UV-visible range.
- Sensitivity : precision of the order of 0.001° depending on the device.
- Types of polarimeters :
- Automatic polarimeters : fast and accurate measurement with digital display.
- Manual polarimeters : suitable for applications requiring fine adjustment.
- Measurement conditions : precise temperature control, particularly for substances sensitive to thermal variations.
- Units of measurement : optical degrees (°) or specific rotational power ([α]).
Polarimetry is often used in conjunction with other analytical techniques, such as chromatography, for more complete characterization of samples.
For which matrices is polarimetry suitable?
Polarimetry ideal method for the analysis of various matrices containing optically active compounds:
and ease of use, polarimetry is an essential tool for industries seeking to guarantee the conformity and quality of their optically active products.
Main industrial applications of polarimetry
Polarimetry used in several industrial sectors for quality control and product conformity:
Léa Géréec
Technical and scientific advisor
