Angle of Rotation
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 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) )
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,
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 is the proportion of the amount of sucrose contained
in the total soluble solid content. Brix value is required for
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 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.
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.
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.
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.