Polarimeters

High-Speed Polarimeter Series – the fastest polarimeter worldwide

A.KRÜSS Optronic manufactures automatic and manual polarimeters for a variety of functions and requirements.
Instruments in the P8000 series are fully automatic and extremely time efficient. With a measuring time of just one second, they are the fastest polarimeters on the global market. They combine speed with the utmost accuracy and resolution of the measuring results.

They are operated on-site using the touchscreen on the device. The measuring results are stored in a database in the device and can be printed out from an external printer or exported onto data carriers.

The Automatic Polarimeter P3000 also functions fully automatically. It stands out due to its particular ease of use, meaning that even staff without specialist knowledge can operate it. As a result, it is especially suited to use near the production area, for example, in quality control. The results can be displayed immediately in degrees ° or in the international sugar scale °Z.

With the manual laboratory polarimeter P1000-LED, A.KRÜSS Optronic provides a classic device for simple laboratory applications and training. The device provides a cost-effective alternative to automatic digital instruments and facilitates direct experience with polarimetry.

 For full technical specifications, please download the brochure here.

KRÜSS Polarimeter – News and Blog

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 Polarimeters

Many chemical substances, particularly biochemical substances, are optically active. They rotate the plane of polarisation of polarised light passing through. The direction of rotation and specific angle α are characteristic sizes of a substance or a solution. They are measured using polarimeters.

Polarimetry is a highly efficient technique for analysing optically active liquids such as sugar solutions, lactic acid and tartaric acid. Measuring the angle of rotation of linear polarised light when it passes through an optically active substance is part of the standard repertoire of chemical, biochemical and pharmaceutical laboratories. It provides valuable information on the chemical structure, chirality and concentration of a sample.

Classic polarimeters operate manually. The brightness of the polarised and rotated light is assessed with the eye and the result read from a scale. The use of a manual polarimeter requires an experienced and qualified operator and takes up a certain amount of time. A modern automatic polarimeter speeds up this process – a precise measurement value is available in just one second. The device’s digital function rules out any measuring errors caused by the user and leads to results that can be reproduced exactly – a crucial factor for measurements used for quality control and process monitoring. Automatic polarimetry is compatible with Good Laboratory Practice (GLP) and US FDA 21 CFR part 11.

Investment in an automated instrument pays off very quickly because it significantly improves productivity in the laboratory. In modern companies in the pharmaceutical, chemical, sugar and food processing industries, an automatic polarimeter is now the absolute state of the art.

Polarisation and polarimetry – physical principles

Electromagnetic waves, including light, have a distinct polarisation plane which is defined by the level of electrical field components. Natural “unpolarised” light consists of the overlapping of a variety of single waves of different polarisations. Waves of a certain polarisation plane can only be filtered out through specific physical effects, such as the reflection on a non-metallic surface. Some insects are able to perceive polarised light and can therefore look through water surfaces, for example. Humans have to use physical instruments to observe polarisation effects.

Polarisation filters are made of a special film that only allows light of one polarisation plane to pass through, absorbing the rest of the light. Photographers use these kinds of filters to eliminate unwanted reflections.

“Optically active substances” are transparent substances which rotate the light passing through the polarisation plane. This is caused by the spatial structure of their molecules. Some substances occur in chemically identical compositions but with molecules in a spatially symmetrical arrangement. Both of these enantiomers rotate the polarisation plane of the light in opposite directions. Examples include sugar or the well-known left-rotating and right-rotating lactic acids in yoghurt. Usually only one of the two enantiomers of the same substance occurs in nature. However, both can occur in chemical synthesis. The different enantiomers of the same substance have different pharmacological effects and therefore have to be separated in pharmaceutical production, e.g. through HPLC detection. The purity of the reaction product can be determined polarimetrically.

In a polarimeter, the unpolarised light from a light source is fed through a polariser. The linear polarised light passing through the polariser passes through the cell with the substance to be tested. The polarisation plane is then rotated. The angle of rotation is determined by the analyser which also only lets through linear polarised light to the observer’s eye. In the polarimeter, polarisers and analysers are set so that no more light can pass through in the case of empty cells. After filling the optically active substance, some light passes through the analyser again. The analyser is then rotated so that it is dark again. The angle of rotation can then be read on a scale. Because the angle of rotation depends on the temperature of the sample and the wavelength of the light used, the optical rotation is stated for defined temperatures. This is usually 20 °C in laboratories. Measurement is usually carried out with light in the sodium D line with a wavelength of 589 nm.

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