Question: What is polarimeter. [CoU-2020]
Answer: A polarimeter is an analytical instrument used to measure the rotation of polarized light by optically active substances. The rotation of polarized light is dependent on the chemical structure of the substance through which it passes, and the polarimeter is able to provide valuable information about the chemical composition and structure of the sample.
Question: Write down the various parts/instrumentation of a polarimeter. [KU-2021, CoU-2020]
Answer: The basic parts of a polarimeter include:
1. Light Source: The polarimeter requires a stable and consistent light source that emits polarized light. The light source can be a sodium vapor lamp or a mercury vapor lamp.
2. Polarizer: The polarizer is used to generate polarized light. It is typically made of a material that transmits only light waves that vibrate in one direction, producing a beam of light with a single polarization.
3. Sample Cell: The sample cell is where the optically active substance is placed. The length of the sample cell is critical for the accuracy of the measurement.
4. Analyser: The analyser is used to detect the rotation of polarized light caused by the optically active substance in the sample cell. The analyser is typically a polarizer. It is positioned at a fixed angle relative to the polarizer.
5. Detector: The detector is used to measure the intensity of the light that passes through the analyser. The detector can be a photodiode or a photomultiplier tube.
6. Control Unit: The control unit is responsible for controlling the polarimeter, including the light source, polarizer, analyser, and detector. It also contains the software and hardware necessary for data acquisition and analysis.
Question: What are the requirements of polarimetric measurement of a chiral molecule? [KU-2021, KU-2019]
Answer: The requirements of polarimetric measurement can vary depending on the specific application and the level of accuracy required. However, some general requirements include:
Polarizer: A polarizer is needed to polarize the light. It can be either linear or circular polarizer depending on the type of measurement required.
Detector: A detector is used to measure the intensity of the polarized light. It can be a photodiode, a photomultiplier tube, or a CCD camera.
Light source: A light source is needed to illuminate the sample. It can be either a monochromatic or a polychromatic source depending on the measurement requirements.
Sample: A sample is required to be measured. It can be a liquid, a solid, or a gas.
Optics: Optics components such as lenses, mirrors, and beam splitters are required to guide and manipulate the light as needed.
Calibration: Accurate calibration is necessary to ensure the accuracy of the polarimetric measurement. Calibration can be achieved by using standard samples of known polarization properties.
Stability: The measurement setup should be stable to ensure consistent and repeatable results. Factors such as temperature, vibration, and humidity can affect the stability of the setup and need to be controlled.
Data analysis: Appropriate data analysis techniques are needed to extract the relevant information from the polarimetric measurement data. These techniques can include statistical analysis, Fourier analysis, and image processing.
Question: State the application of polarimeter. [CoU-2021]
Answer: A polarimeter is an analytical instrument used to measure the angle and amount of rotation of plane-polarized light as it passes through an optically active substance. Here are some common applications of polarimeters:
Chemical analysis: Polarimeters are often used in chemical analysis to measure the concentration and purity of optically active compounds such as sugars, amino acids, and proteins. The specific rotation of a compound can be determined by measuring the angle of rotation of polarized light passing through a solution of the compound.
Pharmaceutical industry: The pharmaceutical industry uses polarimeters to determine the purity and concentration of chiral compounds. Polarimeters are also used to ensure the quality and consistency of pharmaceutical products.
Food industry: Polarimeters are used in the food industry to determine the sugar content of various food products such as fruit juices, honey, and syrups. For example, the specific rotation of sucrose is well-known. So by measuring the rotation of polarized light passing through a sucrose solution, the concentration of sucrose can be determined.
Environmental monitoring: Polarimeters can be used to monitor water quality by measuring the specific rotation of polarized light passing through water samples. This can provide information about the presence and concentration of optically active substances such as organic pollutants, which can have harmful effects on aquatic life.
Research: Polarimeters are used in research to study the optical properties of various materials such as crystals, polymers, and liquid crystals. This information can tell us important things about the structure and properties of those materials.
Quality control: Polarimeters are used in various industries such as pharmaceuticals, food, and cosmetics for quality control purposes. By measuring the specific rotation of a sample, manufacturers can ensure that the product meets the required standards and specifications.
Biomedical research: Polarimeters are used in biomedical research to study the optical properties of biological samples such as cells, tissues, and fluids. This can provide information about the molecular structure and properties of these samples, which can help in the development of new diagnostic and therapeutic methods.
Astronomy: Polarimeters are used in astronomy to study the polarization of light from cosmic objects such as stars and galaxies. This can provide information about the magnetic fields and other physical properties of these objects.
Material science: Polarimeters can be used to study the optical properties of materials such as crystals, fibers, and films. This can provide information about the molecular structure and properties of these materials, which can help in the development of new materials with specific optical properties.
Overall, polarimeters have a wide range of applications in various fields of science, engineering, and industry, where they are used to measure the optical properties of substances and materials.
Question: Write down the factors affecting the angle of rotation in polarimetry. [CoU-2020]
Answer: The angle of rotation is affected by several factors, including:
Nature of the substance: The angle of rotation is directly proportional to the concentration and the specific rotation of the optically active substance. The specific rotation is a constant for a given substance and is a measure of its ability to rotate the plane of polarization of light.
Wavelength of light: The angle of rotation is dependent on the wavelength of light used. Different wavelengths of light are rotated differently, and so the angle of rotation varies with the wavelength of light.
Temperature: The angle of rotation of polarized light passing through an optically active substance also depends on the temperature of the substance. Generally, an increase in temperature causes a decrease in the angle of rotation.
Path length of the sample: The angle of rotation is directly proportional to the path length of the sample. The longer the path length, the greater the angle of rotation.
Presence of other substances: The angle of rotation may be affected by the presence of other substances in the solution. Interference from other substances may cause a decrease in the angle of rotation or may affect the specific rotation of the optically active substance.
pH of the solution: The angle of rotation is also affected by the pH of the solution. Some optically active substances may exhibit different degrees of rotation at different pH levels.
Pressure: Changes in pressure can cause changes in the density and refractive index of the solution, which can affect the angle of rotation.
Solvent: The solvent used to dissolve the optically active substance can affect the angle of rotation. Some solvents may cause changes in the refractive index or specific rotation of the substance.
Instrumentation: The accuracy and precision of the polarimeter used to measure the angle of rotation can also affect the measurement. Any errors or deviations in the instrument can lead to inaccuracies in the measured angle of rotation.
Purity of the sample: The purity of the sample can affect the angle of rotation. Impurities in the sample can cause a decrease in the angle of rotation or may interfere with the measurement.
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