Polarimetry and Refractive Index Measurement Techniques
Classified in Physics
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Abbe Operation
Abbe Operation is based on the determination of the critical angle. The technique is to calibrate the device, usually with distilled water at 20ºC, by matching the shade formed by the prism surface illuminated by a brand (not recorded) in the center of the telescope. Perform the same operation with the test sample to make the correct reading of the refractive index in the eyepiece of the telescope. Since the refractive index varies with temperature, it is important to perform the measurement with the apparatus thermostatted at 20°C or at least know the temperature at which to make the determination.
Understanding Light Polarization
- Natural Light: It is a vibration in all directions perpendicular to the beam.
- Polarized Light: It is a movement in one plane of vibration perpendicular to the beam.
Rotatory Power and Polarimetry
Rotatory Power: Optically active substances are those that provoke a turn in polarized light. These are substances whose molecules do not have any axis of symmetry. Substances that rotate light are called right-handed and left-handed.
Polarimeter: The apparatus used for measuring the optical rotation of solutions.
Polarimetry: A measure of the change of direction of vibration of polarized light when it interacts with optically active materials. It allows us to know the concentration of solutions by determination of their rotatory power since this is proportional to the concentration of solutions. Instead, assume the specific rotatory power of dilute solutions is constant for a given temperature and wavelength.
3 Steps to Perform Measurement
- Adjust the apparatus with distilled water until the darkness disappears and note the reading of the limbo that is usually provided with a vernier.
- Then, the tube is rinsed with the test sample and filled. The twilight zone appears.
- Finally, turn the analyzer until the gloom disappears, and then note the reading of the lamina.
Abbe Operation
Abbe Operation is based on the determination of the critical angle. The technique is to calibrate the device, usually with distilled water at 20ºC, by matching the shade formed by the prism surface illuminated by a brand (not recorded) in the center of the telescope. Perform the same operation with the test sample to make the correct reading of the refractive index in the eyepiece of the telescope. Since the refractive index varies with temperature, it is important to perform the measurement with the apparatus thermostatted at 20°C or at least know the temperature at which to make the determination.
Understanding Light Polarization
- Natural Light: It is a vibration in all directions perpendicular to the beam.
- Polarized Light: It is a movement in one plane of vibration perpendicular to the beam.
Rotatory Power and Polarimetry
Rotatory Power: Optically active substances are those that provoke a turn in polarized light. These are substances whose molecules do not have any axis of symmetry. Substances that rotate light are called right-handed and left-handed.
Polarimeter: The apparatus used for measuring the optical rotation of solutions.
Polarimetry: A measure of the change of direction of vibration of polarized light when it interacts with optically active materials. It allows us to know the concentration of solutions by determination of their rotatory power since this is proportional to the concentration of solutions. Instead, assume the specific rotatory power of dilute solutions is constant for a given temperature and wavelength.
3 Steps for Measurement
- Adjust the apparatus with distilled water until the darkness disappears and note the reading of the limbo that is usually provided with a vernier.
- Then, the tube is rinsed with the test sample and filled. The twilight zone appears.
- Finally, turn the analyzer until the gloom disappears, and then note the reading of the lamina.