Polarimetry Definitions and Applications

Polarimetry Fundamentals

Polarimetry is a sensitive, non-destructive technique for measuring the optical activity exhibited by inorganic and organic compounds. A compound is considered to be optically active if linearly polarised light is rotated when passing through it. The amount of optical rotation is determined by the molecular structure and concentration of chiral molecules in the substance. Each optically active substance has its own specific rotation as defined in Biots law:

The polarimetric method is a simple and accurate means for determination and investigation of structure in macro, semi-micro and micro analysis of expensive and non-duplicable samples. Polarimetry is employed in quality control, process control and research in the pharmaceutical, chemical, essential oil, flavour and food industries. It is so well established that the United States Pharmacopoeia and the Food and Drug Administration include polarimetric specifications for numerous substances.

Research Applications

Research applications for polarimetry are found in industry, research institutes and universities as a means of:

Isolating and identifying unknowns crystallised from various solvents or separated by high performance liquid chromatography (HPLC).
Evaluating and characterising optically active compounds by measuring their specific rotation and comparing this value with the theoretical values found in literature.
Investigating kinetic reactions by measuring optical rotation as a function of time.
Monitoring changes in concentration of an optically active component in a reaction mixture, as in enzymatic cleavage.
Analysing molecular structure by plotting optical rotatory dispersion curves over a wide range of wavelengths.
Distinguishing between optical isomers.

In each of these applications, the AUTOPOL offers up to six discrete wavelength selections to observe the effect of wavelength upon an optically active substance.

Quality and Process Control Applications

Quality and process control applications, both in the laboratory or on-line in the factory, are found throughout the pharmaceutical, essential oil, flavour, food and chemical industries. A few examples are listed below.

Pharmaceutical Industry