Factors Affecting the Measurement of Optical Rotation
The rotation exhibited by an optically active substance depends on the thickness of the layer traversed by the light, the wavelength of the light used for the measurement, and the temperature of the system. In addition, if the substance being measured is a solution, then the
concentration of the optically active material is also involved and the nature of the solvent may also be important. There are certain substances that change their rotation with time. Some are substances that change from one structure to another with a different rotatory power and are said to show mutarotation. Mutarotation is common among the sugars. Other substances, owing to enolization within the molecules, may rotate so as to become symmetrical and, thus, lose their rotatory power. These substances are said to show racem-ization. Mutarotation and racemization are influenced not only by time, but also by pH, temperature, and other factors. Of course, rotations that determined for the same compound under the same conditions are identical. Therefore, in expressing the results of any polarimetric measurement, it is, therefore, very important to include all experimental conditions.
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