Download Citation on ResearchGate | On Jan 1, , Xingyu Zhu and others published Relationship between Refractive Index and Molar Concentration of. Therefore, practical tools are required to test the quality of relationship between the concentration of thymol and refractive index of essential oils as a quality. In optics, the refractive index or index of refraction of a material is a dimensionless number that .. For a more accurate description of the wavelength dependence of the refractive index, the Sellmeier equation can be used. It is an Most commonly it is used to measure the concentration of a solute in an aqueous solution.
However, when the FDA document was published, index of refraction IoR as a method of concentration measurement was limited. It is worth another look at current and emerging technologies to satisfy the spirit of risk-based approaches to manufacturing. IoR is a nonspecific and direct fluid concentration measurement using refractive index, which is the measurement of light refraction.
IoR has been shown experimentally to be a significant if not superior means of detection and identification of process fluids as compared to inline quality control methods like conductivity, pH, and osmolality. Unlike nonspecific indirect methods, IoR can be used to both positively identify and display concentration measurements. Furthermore, previous experiments have shown the usefulness of IoR as a quality control metric for buffers and media components.
- Concentration Measurement with Refractive Index
Positive identification and quantification of biopharmaceuticals and other protein-based products during manufacturing are often performed by taking a sample and using offline tests including: The newer IoR technology works well for highly ionic solutions and nonionic chemistries. This tutorial outlines applications for the IoR method as PAT for monitoring and control of biopharmaceutical purification processes. Included are examples of key process steps where the technology can be used.
Entegris IoR Concentration Monitors Cell Removal and Clarification The process of removing cells and cellular debris from a harvested culture prior to purification is typically performed using depth filtration, tangential flow filtration, centrifugation, or a combination of methods. Filters are often placed downstream in order to capture any material that escapes the separation method.
IoR can also identify buffers for diafiltration and recovery of product, while detecting even small concentrations of cells or cellular debris breakthrough.
Due to this identification and detection, processes can be designed to bypass cellular breakthrough filters until, and only if, they are needed. This can lead to a cost savings. During MF and depth filtration, IoR monitors optimize the diafiltration process by detecting when a product is below its target concentration. Utilizing real-time IoR monitors enhances these processes by reducing process time and product dilution. Affinity Chromatography In many processes, affinity chromatography performs most of the product purification process.
During cell removal, IoR monitors can identify each incoming buffer that prepares and equilibrates the cell removal system. Especially during affinity chromatography, an incorrect buffer can inadvertently damage the resin, causing thousands of dollars in lost material, before processing even begins. Regarding inadequate resin concentration, IoR monitors detect product breakthroughs, channeling, or high asymmetry in the bed, potentially saving product loss.
Moreover, topological insulator material are transparent when they have nanoscale thickness. These excellent properties make them a type of significant materials for infrared optics. The refractive index measures the phase velocity of light, which does not carry information.
This can occur close to resonance frequenciesfor absorbing media, in plasmasand for X-rays. In the X-ray regime the refractive indices are lower than but very close to 1 exceptions close to some resonance frequencies. Since the refractive index of the ionosphere a plasmais less than unity, electromagnetic waves propagating through the plasma are bent "away from the normal" see Geometric optics allowing the radio wave to be refracted back toward earth, thus enabling long-distance radio communications.
See also Radio Propagation and Skywave.
Concentration Measurement with Refractive Index
Negative index metamaterials A split-ring resonator array arranged to produce a negative index of refraction for microwaves Recent research has also demonstrated the existence of materials with a negative refractive index, which can occur if permittivity and permeability have simultaneous negative values.
The resulting negative refraction i. Ewald—Oseen extinction theorem At the atomic scale, an electromagnetic wave's phase velocity is slowed in a material because the electric field creates a disturbance in the charges of each atom primarily the electrons proportional to the electric susceptibility of the medium.
Similarly, the magnetic field creates a disturbance proportional to the magnetic susceptibility. As the electromagnetic fields oscillate in the wave, the charges in the material will be "shaken" back and forth at the same frequency. The light wave traveling in the medium is the macroscopic superposition sum of all such contributions in the material: This wave is typically a wave with the same frequency but shorter wavelength than the original, leading to a slowing of the wave's phase velocity.
Most of the radiation from oscillating material charges will modify the incoming wave, changing its velocity.
However, some net energy will be radiated in other directions or even at other frequencies see scattering. Depending on the relative phase of the original driving wave and the waves radiated by the charge motion, there are several possibilities: This is the normal refraction of transparent materials like glass or water, and corresponds to a refractive index which is real and greater than 1.
This is called "anomalous refraction", and is observed close to absorption lines typically in infrared spectrawith X-rays in ordinary materials, and with radio waves in Earth's ionosphere.
It corresponds to a permittivity less than 1, which causes the refractive index to be also less than unity and the phase velocity of light greater than the speed of light in vacuum c note that the signal velocity is still less than c, as discussed above.