Polarimetrillä

Polarimetrillä, literally using a polarimeter, refers to the method of measuring the rotation of polarized light as it passes through optically active substances. The technique is based on the difference in refractive indices for left‑ and right‑hand circularly polarized components of light. When unpolarized or linearly polarized light enters a sample that contains chiral molecules, the plane of polarization is rotated by an angle proportional to the concentration of the optically active species, the path length of the sample, the wavelength of the light, and the specific rotation of the substance.

The first polarimeters were proposed in the early 19th century by Legendre and later refined by Malus. Modern instruments are generally automated, with a light source (often a monochromatic laser or LED), a polarizer, the sample cell, an analyzer, and a detector such as a photodiode or photomultiplier. High‑precision polarimeters can detect rotation changes to ≤10⁻³ degrees, enabling applications in pharmaceuticals, food science, environmental monitoring, and materials research.

In analytical chemistry, polarimetry is routinely used to determine the purity of sugars, amino acids, and pharmaceuticals by measuring their specific rotation values. The method also plays a role in the authentication of natural products, such as essential oils and herbal extracts. In biochemistry, circular dichroism spectroscopy, a related technique, provides information on protein secondary structure.

Polarimetry extends into astronomy, where polarimeters attached to telescopes measure the polarization of starlight to infer properties of interstellar dust and magnetic fields. In condensed matter physics, polarimeters help characterize liquid crystals and anisotropic materials.

Overall, polarimetrillä remains a fundamental, non‑destructive analytical technique that complements spectroscopic and chromatographic methods across diverse scientific disciplines.