polarisimetrar

Polarimeters are analytical instruments used to measure the angle of rotation that plane-polarized light undergoes when passing through an optically active substance. The device is fundamental in chemistry, biochemistry, and pharmacology for determining the optical purity, concentration, and specific rotation of chiral compounds. Optical activity arises from the asymmetric structure of molecules, causing them to rotate polarized light either clockwise (dextrorotatory) or counterclockwise (levorotatory).

The basic design of a polarimeter consists of a light source, a polarizer, a sample holder, an analyzer, and a detector. Light from the source is polarized through the first polarizer before passing through the sample. If the sample is optically active, it alters the plane of polarization. The analyzer, positioned at a variable angle, then blocks or transmits light based on this rotation. The angle of rotation is read directly from a calibrated scale or digitally, providing quantitative data.

Polarimeters are commonly used in quality control for pharmaceuticals, where the enantiomeric purity of chiral drugs is critical. They also play a role in studying carbohydrate solutions, amino acids, and other biologically relevant molecules. Modern polarimeters may incorporate digital sensors and automated data logging for enhanced precision and ease of use.

The principle of operation relies on the relationship between the observed rotation angle, the concentration of the optically active substance, and the path length of the sample. This relationship is expressed as the specific rotation, a characteristic property of a compound that helps identify and quantify it. While polarimeters are highly effective for chiral analysis, they do not provide structural information about the molecule itself.