Optical rotation is a phenomenon wherein light vibrating in one fixed direction (polarized light) passes through a liquid sample and rotates. The point at which it tilts is called the "angle of rotation." It is the basic value measured with a polarimeter. The angle of rotation changes depending on the concentration of the liquid sample, the length of the observation tube, the temperature, and the measurement wavelength. The unit is expressed as, " °.
Specific Rotation
Specific rotation is a characteristic value related to optical activity, standardized for each and every substance. There are set values determined for every substance, printed in literature such as chemistry handbooks. As a definition, it corresponds with the angle of rotation of a sample at 100% concentration measured with a 100mm observation tube. The unit is expressed as, " °."
⇒specific rotation = (10000 × angle of rotation) / (length of observation tube (mm) × concentration (g/100mL) )
Concentration
The density of a solution made when dissolving an optically active substance in optically inactive water and alcohol is called "concentration." The unit is expressed as, "g/100mL."
⇒concentration (g/100mL) = (100 × angle of rotation (measurement value obtained with a polarimeter) ) / (length of observation tube (dm) × specific rotation)
* 1dm = 10cm
International Sugar Scale
A scale converted from the angle of rotation. The unit is expressed as, "°Z." 26g/100mL of sucrose solution measured with a 200mm observation tube at 20°C is 100°Z. This scale is used in the sugar refining industry. As with the Brix scale for sugar level, temperature compensation is necessary. Sucrose solution of 100°Z is 23.70% Brix.
⇒ International Sugar Scale = angle of rotation × 2.888
Purity
Purity is the proportion of the amount of sucrose contained in the total soluble solid content. Brix value is required for Purity measurement. The unit for Purity is expressed as, "% ."
⇒ Pol = (26.016/100mL of mass (density) ) × International Sugar Scale
* sucrose amount is referred to as "Pol."
⇒ Purity = (Pol / Brix) × 100
OD
OD refers to "optical density." It is also called, "absorbance."
For a given wavelength of light, supposing the transmittance of water is 100%, OD of 10% is 1.0, transmittance of 1% is OD of 2.0, and for transmittance of 0.1%, the OD is 3.0.
In regards to polarimeters, OD illustrates the densest darkly colored liquid that is capable of being measured.
ICUMSA
(International Commission for Uniform Methods of Sugar Analysis)
Known as the "International Sugar Analysis Standardization Committee" in Japanese, ICUMSA is an international organization unifying the activities of sugar analysis committees from several countries.
Measurement Wavelength
(λ)
The angle of rotation will change depending on the wavelength of the light source used by a polarimeter. Almost all polarimeters use the Sodium D-line wavelength of 589.3nm. The SAC-i 589/882 is capable of measurement not only at 589nm, but it can also be changed to measure at a wavelength of 882nm.
Observation Tube
Most polarimeters measure angle of rotation by filling the inside of tubes, called observation tubes, with liquid sample and passing light through them. Observation tube lengths of 100mm and 200mm are the most prevalent.
200mm observation tubes are primarily used in the sugar refining industry, and 100mm observation tubes are largely used in the pharmaceutical industry. There are also short-type observation tubes of lengths such as 10mm.
* RePo series does not use observation tubes.
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