Polarimetry Applications in Industry, Research, and Development
Analysis of optically active substances by determining the angle of rotation
A polarimeter is a device used to determine the direction of polarization of light and the optical rotation of optically active substances. These substances include sugars, amino acids and other chiral molecules. That is why polarimetry is an important analytical method in chemistry, pharmacy, food analysis, and biochemistry. The measurement distinguishes between two variables.
-
Angle of rotation – This is the measured value that indicates the rotation of the plane of polarization.
-
Specific angle of rotation – This is the value that takes into account the concentration of the sample and the length of the measurement tube.
To reliably determine these measurement variables, the polarimeter must accurately measure the path of the polarised light and the resulting rotation. This raises the question of how a polarimeter is technically constructed and how the measurement process works.
Contents
How does a polarimeter work?
The analytical instruments measure the change in the plane of polarization of linearly polarized light after it has interacted with an optically active (chiral) substance (e.g. sugar). In this interaction, the polarization direction of the light wave is rotated by a certain angle—the angle of rotation.
Example: Sucrose (bottom) rotates the polarization plane clockwise, while fructose (top) rotates it counterclockwise. This allows the two substances to be clearly distinguished from each other.
The angle of rotation provides valuable information about the molecular structure, purity, and concentration of the substance being analyzed.
The functionality of this analytical method can only be fully understood if certain properties of the analyzed samples are known. This is because not every substance affects polarized light – this ability is linked to certain features and influences.
Sample Properties and Influences on the Measurement
chirality
Chirality describes the fundamental property of a molecule that it is not superimposable on its mirror image. The optical activity utilized in polarimetry occurs only in chiral molecules. Their spatial structure corresponds to a mirror image that cannot be aligned by rotation. One example is our own hands: the left hand corresponds to the molecule, the right to its mirror image – despite rotation, they never fit exactly on top of each other.
Many chemical compounds show exactly this behavior. Due to their lack of symmetry, they can rotate the plane of polarization of light. This optical activity is measured and provides information about the structure, purity, and composition.
Influences on the measurement
Optical activity—and thus the measured value—is influenced by temperature, the wavelength of light, and the optical path length. The optical path length is determined by the length of the measurement tube or cuvette used. The rule of thumb is that a longer optical path results in a larger angle of rotation. As the concentration rises, the angle of rotation also rises. In the case of temperature and wavelength, whether increasing these parameters results in a larger or smaller angle of rotation depends on the substance being studied.
Example: While the angle of rotation for sucrose decreases as the temperature rises, the opposite is true for quartz—it increases as the temperature rises.
Enantiomers
Enantiomers are specific pairs of mirror-image molecules. They can also be compared well with our hands: Both hands consist of the same “components” – palm and five fingers – but it is not possible to make the two hands congruent by arbitrary rotation.
Enantiomers have the same molecular formula and the same bonds, but differ in their spatial arrangement, being mirror images of each other. These mirror-image forms can have very different properties – one Enantiomers can taste sweet, the other bitter. Example: Limonene = R-limonene smells like orange, S-limonene smells like lemon. For medicinal products: Example: Ibuprofen = drug with R- and S-enantiomer (only the S-enantiomer is pharmacologically active)
The Meaning of Chirality and Enantiomers
Many pharmacologically active substances are chiral and therefore exist as Enantiomers. Although enantiomers have the same molecular formula and nearly identical physical properties—such as density or refractive index—they are difficult to distinguish or separate using conventional methods or techniques such as HPLC (high-performance liquid chromatography). That is precisely why methods such as polarimetry are so important, because they make use of a property that varies: optical activity.
Modern devices such as a KRÜSS Optronic polarimeter enable high-precision measurements of the angle of rotation and deliver reproducible results even with very low concentrations or sensitive samples. Thanks to their innovative assistance systems, these instruments are particularly well-suited for pharmaceutical quality control and research.
Why Enantiomers Are Studied in the Pharmaceutical Industry
Despite their structural similarity, enantiomers can have completely different biological effects . The reason: they interact differently with enzymes, receptors, and other biological target structures, which are themselves chiral. This results in some major differences in:
- Mechanism of action
- Pharmacological activity
- Toxicity
- Side effects
- sensory properties (e.g. smell, taste)
Example: The substance thalidomide – in the sleeping pill thalidomide it was present as a racemate (enantiomer ratio 1:1). One of the enantiomers had a teratogen effect, i.e. when taken, it caused malformations in pregnancy on the embryo. The tragic incidence surrounding the production of thalidomide prompted the introduction of legal guidelines in many countries. We now have standards, that specify the exact rules to be followed during the development of chiral drugs.
In order to meet the high standards of the pharmaceutical industry and food production, we have developed state-of-the-art assistance systems that guarantee analysis of optically active substances at the highest level.
Polarimeters for highly regulated sectors
P9000 series: Safe. Compliant. Fully automatic.
With its new P9000 series, KRÜSS Optronic is setting new standards in polarimetry. The polarimeters feature innovative assistance systems, intelligent sample monitoring, and stable temperature control to within ±0.1°C.
- The sample can be filled directly in the temperature-controlled measurement devices and checked live via camera. Air bubbles, particles, inhomogeneities and temperature gradients are reliably detected and avoided.
- A status LED signals that the system is ready to measure, while the system continuously checks the stability of the measured values and only accepts values that meet defined quality criteria.
The P9000 series delivers reliable results, saves time & meets the highest regulatory requirements such as 21 CFR Part 11 and EU Annex 11.
Video assistance systems P9000 series
Watch the P9000 series product video
Standards and guidelines
Certified measurement quality according to global standards
You can use a polarimeter to determine characteristic properties of substances without chemically altering or destroying them. These analyzers are used in accordance with normative specifications, especially for sensitive and highly regulated applications. The measurement devices must comply with industry standards (e.g. e.g. GMP, GAMP 5) or provide functions required by standards, e.g. in accordance with 21 CFR Part 11 (e.g. audit trail).
Standards in polarimetry establish best practices for environmental conditions and sample preparation, as well as measurement tolerances, specifications, and equipment requirements for devices or calibration devices. If you use the analyzers in accordance with standard specifications, you can ensure that measurements are carried out correctly and according to reproducible procedures.
Below is an overview of all standards and guidelines known to us that refer to polarimetry. Note:This is a general overview of the standards. We would be happy to discuss which specifications the different polarimeter models from A.KRÜSS meet in a personal consultation. Please feel free to contact us.
Polarimeter Standards Overview
Samples and measured values
Angle of rotation of optically active substances for every industry
The measurement involves determining the angle of rotation of optically active substances in liquids. The values obtained are used for quality control in the manufacture of active pharmaceutical ingredients and for the identity testing of chiral substances in the incoming and outgoing goods laboratories.
In the food, starch, and sugar industries, polarimetric measurements are used to determine concentration and purity. Since every industry has its own specific requirements for this measurement technology, we offer a wide selection of different devices and measurement tubes to meet those needs.
Which substances can be measured?
Below is a comprehensive overview of various samples and their specific angles of rotation. Most of the data refer to standard measurement conditions (T = 20 °C and λ = 589 nm). Deviating conditions are noted accordingly.
Note: This overview provides an initial orientation. Which models are best suited to your specific measurement tasks in a personal consultation. Contact us at any time.
Typical areas of application
Wide range of applications. Precise results.
The analysis of optically active substances is one of the most important methods of quality control in the pharmaceutical, chemical, cosmetics, food, and beverage industries. Cette méthode peut être utilisée pour déterminer l’identité et la qualité des substances, ainsi que leur concentration dans les mélanges. The progress of reactions and substance conversions can also be investigated.
The pharmaceutical industry uses these measurement devices to ensure complete separation of enantiomers, to determine the concentration of optically active substances, or to analyze the relationships between toxicological and pharmacological properties.
In food production, analytical instruments are used to verify the purity of raw materials or to provide information about product quality. The range of applications for these measurement devices is wide.
For information: Below is an overview of typical areas of application, substances tested, associated standards and the KRÜSS Optronic polarimeters recommended by us.
How to use – Product videos
Depending on the application, we offer a variety of polarimeter solutions, calibration standards, and accessories.
- In addition to our new P9000 series, we continue to offer the tried-and-true P8000 series with water-based sample temperature control.
- The P1000-LEDis used primarily for educational purposes; it measures optical rotation based on the half-shade principle.
- An economical solution is the P3000 model: It is used when a measurement accuracy of ±0.01° is sufficient.
- With PTB-certified quartz reference plates (compliant with OIML, ICUMSA, and Pharmacopoeia standards), the calibration and adjustment of KRÜSS Optronic measurement devices can be performed precisely and easily.
How to use – Product videos
3 Videos
0:16
0:16
0:16
Documents
Upload files in this category Drag und Drop Ihrer Datei hierher Upload a folder Upload files
