28 Why Measure the Refractive Index?
The refractive index of a pure material is a physical property which you can use to identify and characterise samples. For binary mixtures, e.g. dissolved substances, the refractive index is a measure of concentration. For ternary or multi-component mixtures of a given mixing ratio, you can monitor the refractive index for quality control.
As refractive index measurements are quick and reliable, the method is the state of the art in industries around the globe. Measuring refractive index is an essential part of numerous standard operating procedures and laboratory analyses.
A measuring principle with clear benefits
Anton Paar refractometers use reflected rather than transmitted light to measure the refractive index. In this approach the sample on top of the measuring prism is irradiated from different angles by an LED. At the interface between sample and prism the incident beam is either refracted into the sample or reflected back into the prism. The reflected beam is detected by a sensor array. From this the critical angle for total reflection is calculated and used to determine the refractive index (RI) of the sample.
Your benefits of this technology are:
Economic use of sample • You only require a few microlitres • The sample can be recovered as the measurement is non-destructive
Fast and easy • You do not have to prepare your sample • Just apply sample and get a reading within seconds • A quick wipe cleans the prism after each run
Highly tolerant
• Independent of sample properties you can measure: - all samples from liquids to pastes, polymers to solids - turbid, coloured or opaque samples - liquids containing air bubbles or solid particles
• There is no influence from vibrations or other environmental disturbances
Long-lasting • There are no moving parts you need to change • A long-life LED is used as the light source
ADVERTORIAL
Every Sample has a Refractive Index Drugs:
The production of pharmaceuticals is very demanding. Many national and international drug regulations and quality standards need to be fulfilled. This includes a precise identification and purity control of the raw materials as well as the final products. Anton Paar refractometers are designed to meet the standards of international pharmacopoeias. They provide 21 CFR Part 11 compliance.
Phytopharmaceuticals:
Plants containing pharmaceutical drugs can be used for medical treatment. As they are natural products, their composition depends on several environmental parameters and the concentration of the medical drugs they contain varies in a wide range. Abbemat refractometers provide correct identification and concentration measurements.
Perfume:
In perfume manufacturing, Abbemat refractometers in combination with DMA density meters and MCP polarimeters are used to carry out purity measurements on valuable essential oils and to assure the constant quality of the perfumes.
Food flavours:
Natural and artificial flavors give all of our daily food its distinctive taste. In food production, incoming raw materials and finished products are characterised and tested for purity with Abbemat refractometers in combined setups with MCP polarimeters and DMA density meters.
Juices and syrups:
For economic transport and stocking, fruit juices are often concentrated to save weight and volume. Before bottling, they need to be diluted to a drinkable concentration. The concentration is measured in % Brix with Anton Paar refractometers.
Concrete:
Additives in the concrete mixture influence the material properties. They are used as anti-freeze agents, to adjust the time for setting, and influence the desired texture. Abbemat refractometers have proven ideal for concentration measurements and quality control of such additives.
Sugar:
In order to maximise the yield in sugar manufacturing, the most important analytical parameters to monitor are Pol (°Z), %Brix (RDS) and Apparent Purity. For these measurements an Abbemat refractometer is directly connected to an MCP Sucromat, which then displays all these values simultaneously.
Nanoparticles:
The size distribution of nanoparticles is determined by laser diffraction measurements analysed by inverse scattering theory – a method which requires the refractive index value at the used laser wavelengths. Abbemat MW refractometers are used to determine these RI values. They can also measure very low concentrations of particles which tend to be hardly soluble.
Coffee:
To ensure that coffee grounds contain at least the minimum extract content, as required by regulations, producers use Abbemat refractometers to determine the content of dry substance in the extract. The end result: a cup of coffee that tastes good and has the expected strength.
Soft matter research:
Phase transitions such as sol-gel transitions manifest themselves as changes in the volume and refractive index with temperature. Abbemat HT high- temperature refractometers are used to investigate such material behaviour. Refractometers are ideal here as they do not exert pressure on the sample and are not disturbed by other influences.
Circle no. 101
INTERNATIONAL LABMATE - MARCH 2011 - ADVERTORIAL
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