Polarisimeters

A polarimeter is a scientific instrument used to measure the angle of rotation of plane-polarized light by an optically active substance. This rotation is caused by the interaction of polarized light with molecules that are chiral, meaning they exist in non-superimposable mirror-image forms. Optically active substances, such as sugars, amino acids, and certain steroids, exhibit this property.

The basic principle of a polarimeter involves passing plane-polarized light through a sample contained within a tube. A polarizer creates the plane-polarized light. As this light passes through the optically active sample, its plane of polarization is rotated. A second polarizer, called an analyzer, is then rotated until the light is extinguished or appears at its minimum intensity. The angle through which the analyzer is rotated directly corresponds to the specific rotation of the substance, which is a characteristic property and can be used for identification and quantification.

Polarimeters are widely used in various fields, including chemistry, pharmaceuticals, and food science. In chemistry, they are essential for determining the enantiomeric excess or purity of chiral compounds, which is crucial for drug development and synthesis. In the food industry, polarimetry is employed to measure the sugar content of products like honey, fruit juices, and molasses. The accuracy and sensitivity of polarimeters have led to their widespread adoption as a standard analytical tool for characterizing optically active materials.