Refractometry

The two most commonly used measurement principles are still the Fresnel type and the deflection type. Different designs of the deflection type are marketed by Waters Assoc., Siemens, Winopal Forschung and Dr, Ing. Herbert Knauer. All brands of the Fresnel transmittance type seem to be of the same design. Laboratory Data Control. 

The optical conditions are such that the total intensity of the refracted beam is virtually constant. 

In the Fresnel type, the intensity of the refracted beam is measured. The optical conditions are such that this intensity is a steep function of the refractive index of the liquid. Therefore, the beam is sent from glass into the liquid at an angle of incidence that approximates to the critical angle. Instruments based on this principle have provisions for changing the angle of incidence of the beam in order to fulfill this requirement. 

In order to avoid illumination of the photodetector by the beam reflected at the first interface, the intensity of the broken beam is measured after diffuse reflection at the rear wall of the cell. Compensation for the refractive index of 

The relative performances of the two principles were unclear until recently. 

The refractive index is an important quantity for characterizing the structure of polymers. This is because it depends sensitively on the chemical composition, on the tacticity, and - for oligomeric samples - also on the molecular weight of a macromolecular substance. The refractive indices (determined using the sodium D line) of many polymers are collected in the literature. In order to characterize a molecule s constitution one requires knowledge of the mole refraction, Rg. For isotropic samples, it can be calculated in good approximation by the Lorentz-Lorenz equation  

The refractive index is a useful physical property of liquids. Often, a liquid can be identified from a measurement of its refractive index. The refractive index can also provide a measure of the purity of the sample being examined. This is accomplished by comparing the experimentally measured refractive index with the value reported in the literature for an ultrapure sample of the compound. The closer the measured sample s value to the literature value, the purer the sample. 

The refractive index has as its basis the fact that light travels at a different velocity in condensed phases (liquids, solids) than in air. The refractive index n is defined as the ratio of the velocity of light in air to the velocity of light in the medium being 

The superscript indicates the temperature, and the subscript indicates that the sodium D line was used for the measurement. If another wavelength is used for the determination, the D is replaced by the appropriate value, usually in nanometers (1 nm =10 m). 

Notice that the hypothetical value reported has four decimal places. It is easy to determine the refractive index to within several parts in 10,000. Therefore, is a very accurate physical constant for a given substance and can be used for identification. However, it is sensitive to even small amounts of impurity in the substance measured. Unless the substance is purified extensively, you will not usually be able to reproduce the last two decimal 

2 The Abb6 The instrument used to measure the refractive index is called a refractometer. Al- 

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Purity. This is a widely used expression in the industry and represents, as a percentage, the proportion between polarization (considered a measure of sucrose) and dry soHds (usually obtained by refractometry). 

Fig. 11 Elution profile of the ws-material from microwave-heated spruce chips after SEC [218]. Detection by refractometry index (Rl) dotted line) and UV detection at 280 nm (full line). The arrows mark the elution volume of acetylated GGM fractions...

Refractometry (dn/dc) the LALLS Optical Solutions of f VA and PCP with known concen-... 

Haubenreisser W., Lehmann J., Perthel R., Willsch R., Fiber optic refractometry, Experimentelle Technik der Physik 1984 32 519. 

In addition, typical methods of sensing are total internal reflection fluorescence or monitoring of fluorescence resonance energy transfer6,7. The second class is a direct optical detection principle which relies either on reflectometry or refractometry. The latter is connected to evanescent field... 

Hyphenated techniques like combination of optical detection methods based on reflectometry or refractometry and separation techniques are of future interest. The same is valid for the intention to couple SPR or RIfS with mass spectrometry like MALDI33. 

It is worth stressing that in the use of the coated LPG as a refractometer, and not as chemical sensor, the sPS layer acts just as a passive HRI layer and no chemical interaction with surrounding medium occurs. Therefore, any HRI overlay could be used for the refractometry, not necessarily a chemo-sensitive one as the sPS. However, in this work the same material has been used for both applications taking advantage of the experience ripened in its deposition. 

Skivesen, N. Horvath, R. Pedersen, H. C., Multimode reverse symmetry waveguide sensor for broad range refractometry, Opt. Lett. 2003, 28, 2473 2475... 

Brandenburg, A., Differential refractometry by an integrated optical Young interferometer,... 

Refractometry Using Nanoporous-Silica-Supported and Freestanding Waveguides... 

Droplet temperature is of interest in practical spray processes since it influences the associated heat and mass transfer, chemical reactions, and phase changes such as evaporation or solidification. Various forms of Rayleigh, Raman and fluorescence spectroscopies have been developed for measurements of droplet temperature and species concentration in sprays.16471 Rainbow refractometry (thermometry), polarization ratioing thermometry, and exciplex method are some examples of the droplet temperature measurement techniques. 

As indicated, the specific refractive index increment is best measured by differential refractometry or interferometry. Experimental procedures as well as tabulated values of dn/ dc for many systems have been presented elsewhere40,63K The relevant wavelength and temperature are those used for LS. The value of X0 is invariably 436 or 546 nm, but with the advent of laser LS, values of dn/dc at other wavelengths are required. These can be estimated with good reliability using a Cauchy type of dispersion (dn/dc a 1/Xq). For example the values of dn dc for aqueous solutions of the bacterium T-ferrioxidans at 18 °C are 0.159, 0.141 and 0.125 ml/gm at X0 = 488, 633 and 1060 nm respectively64 ... 

Evaluations of Rd and Y necessitate a knowledge of certain physical properties of the two liquids and the mixtures. The variation of refractive index with concentration is measured readily by refractometry, if I nT, — n21 is large. The coefficient of isothermal compressibility of a mixture t2 requires specialised equipment. Alternatively, it can be determined from the heat capacity and the coefficient of isentropic compressibility87, 88, the latter being yielded from velocity of sound data88. However, provided and 02 for the pure compounds are known, j312 is evaluated most conveniently on the basis of additivity, thus ... 

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