Refractometric measurements, . Refractive index

Refractive Index. The refractometric value of sugar solutions is used as a rapid method for the approximate determination of the soHds content (also known as dry substance), because it is assumed that the nonsugars present have a similar influence on the refractive index as sucrose. Measurement is usually carried out on a Brix refractometer, which is graduated in percentage of sucrose on a wt/wt basis (g sucrose/100 g solution) according to ICUMSA tables of refractive index at 20.0°C and 589 nm. Tables are available that give mass fraction corrections to refractometric values at temperatures different from 20°C. 

Clarification by removal of casein with such agents as calcium chloride, acetic acid, cooper sulfate, or rennin has often been employed to obtain a serum more suitable for refractometric measurements. Obviously the composition, and hence the refractive index, of such sera will depend on the method of preparation. Furthermore, some of the serum proteins may be precipitated with the casein by some of the agents used, particularly if the milk has been heated. Refractive index measurements of such sera are not generally considered as satisfactory as freezing point measurements for detection of added water (David and MacDonald 1953 Munchberg and Narbutas 1937 Schuler 1938 Tell-mann 1933 Vleeschauwer and Waeyenberge 1941). Menefee and Overman (1939) reported a close relation between total solids in evaporated and condensed products and the refractive index of serum prepared therefrom by the copper sulfate method. Of course, a different proportionality constant would hold for each type of product. 

This approach is based on the introduction of molecular effective polarizabilities, i.e. molecular properties which have been modified by the combination of the two different environment effects represented in terms of cavity and reaction fields. In terms of these properties the outcome of quantum mechanical calculations can be directly compared with the outcome of the experimental measurements of the various NLO processes. The explicit expressions reported here refer to the first-order refractometric measurements and to the third-order EFISH processes, but the PCM methodology maps all the other NLO processes such as the electro-optical Kerr effect (OKE), intensity-dependent refractive index (IDRI), and others. More recently, the approach has been extended to the case of linear birefringences such as the Cotton-Mouton [21] and the Kerr effects [22] (see also the contribution to this book specifically devoted to birefringences). 

The (dynamic) range describes the span of the values of the measurand that can be measured by the sensor. In refractometric SPR sensors the dynamic range usually describes a range of values of the refractive index of the sample that can be measured with a specified accuracy. Dynamic range of SPR biosensors defines the range of concentrations of an analyte which can be measured with specified accuracy and extends from the lowest concen-... 

ASTM D542 describes two methods, viz., i) refractometric and ii) microscopic, for the measurement of refractive index of transparent organic plastics. Both the methods require optically homogeneous specimens of uniform index. The ASTM recommends that refractometric method is to be... 

For the refractometric method, the apparatus consists of an Abbe refractometer, a suitable source of white light and a small quantity of suitable contacting liquid. The test specimen for refractometer method should be 12.7x6.3 mm, with one flat face and one perpendicular surface. The two surfaces (preferably polished) shall intersect along a sharp line (without a rounded edge). The test specimen is attached to the prism of the refractometer with a drop of liquid of refractive index higher than the test specimen by at least 0.01 and it should not soften or dissolve the specimen. ASTM D542 suggests a list of liquids for a variety of plastics. Measurements are to be carried out at specified conditions, 296 2 K, and 50 5 per cent RH. Temperature is to be accurately controlled. For maximum accuracy. Sodium D lines are recommended. 

---