Refractometric measurements

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). 

Lauder (1948) also gives data for the rate of hydration of acetaldehyde based on dilatometric and refractometric measurements. He did not realize the catalytic nature of the reaction, and worked in unbuffered solutions which presumably contained small but variable quantities of acetic acid this may account for the erratic nature of his results and for the fact that his rates decrease with increasing temperature. It is more difficult to explain the fact that most of his recorded rates are considerably lower than the minimum (water-catalysed) velocity obtained by other methods. He used concentrated solutions of acetaldehyde, which may have contained considerable quantities of the hemihydrate (MeCH0H)20. The presence of this species has been recently suggested by Ahrens and Strehlow (1965) on the basis of N.M.R. spectra there is evidence for the existence of analogous species in aqueous formaldehyde solutions (Bezzi et al., 1951), and the hemihydrate (CH2CI. CH0H)20 can be isolated as a solid (Natterer, 1882). 

Refractometric measurements can often be used for the rapid measurement of solution concentration. Several standard instruments (Abbe, Pulfrich, etc.) are available commercially. A sodium lamp source is most usually used for illumination, and an instrument reading to the fourth decimal place is normally adequate for crystallization work. It is advisable that calibration curves be measured, in terms of temperature and concentration, prior to the study with the actual system. 

Neumann, G. (1996) Interferometric and refractometric measurements on fluids — Development of new detectors for supercritical fluid chromatography (SFC) (in German), Doctoral dissertation, University of Bochxim, Germany. 

Timoshenko N. I., Kholodov E. P., Tatarinova T. A. Virial coefficients and thermodynamic properties of Freon-23 from Refractometric Measurements.—Thermophysical Properties of Substances and Materials. Gosstandart SSSR, GSSSD, 1975, 8, p. 27—40. 

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. 

The lower limit of the elastic range, the glass transition temperature, can be easily determined by refractometric, volumetric, or other well known methods. The upper limit suffers from an exact definition the transition from the fixed liquid to the liquid state occurs without transformation. But as the viscosity decreases exponentially with the temperature it is very convenient to define a 1 flow-temperature by penetrometer measurements. If the rate of temperature rise is kept constant, this temperature is reproducible within 1° or 2°C. The penetrometer indicates a temperature where macroscopically one would call the substance liquid. ... 

The conservation of mass equations are used with refractometric optics. The absorption optical system will give absorbance (optical density) which is directly proportional to concentration. Unless conservation of mass equations are used, one can only obtain concentration differences from refractometric optics. The Rayleigh optical system will give information proportional to cr — cTm thus Equation 20 or 23 would have to be used to obtain cTm. Note also that the initial concentration c0 is needed. This must be measured by differential refractometry, by boundary-forming experiments, or from ultraviolet light absorption. 

The expression of results in analytical chemistry is mostly in SI units (all base units except the candela and many derived units). The principles to be followed to achieve the comparability and traceability of measurements to the SI have been clearly stated [1,2]. However, certain types of measurements are expressed in conventional units. Turbidity evaluation in water quality analysis, determination of soluble content of fruit and vegetable products by the refractometric method, measurement of caking power of hard coal by the Roga test, determination of the octane number of fuel and seric protein analysis are some examples. 

Procedure Prepare a 50% (w/w) sample solution in water. Adjust the pH to 7.0 0.2 with 1% sodium hydroxide or 1% hydrochloric acid. Filter through a 0.45-pim pore-size membrane filter, using a vacuum and a diatomaceous earth filter aid (1% on solids) if necessary. Discard the first portion of the filtrate if it is cloudy. Determine the density and concentration of solids, in grams per milliliters, refractometrically. Rinse the measuring cell three times with the sample solution, and then fill the cell. Measure absorbancy (As) at 420 nm Calculate the color in ICUMSA units (IU) as follows ... 

Temperature Corrections for Refractometric Sucrose Solutions with Measurements at 20° and 589 nm... 

C, equilibrium pressure cell/shake flask-refractometric method, measured range 10-110°C,... 

Gowman and Ethier [49,50] developed an automated laser-based refractometric technique to measure the solute concentration gradient during dead-end filtration of a biopolymer solution. This paper attempts to reconcile theory with experimental data. The refractometric technique may be useful to other researchers working on quantification of membrane fouling. 

Cowman, L.M. and Ethier, C.R., Concentration and concentration gradient measurements in an ultrafiltration concentration polarization layer. Part I A laser-based refractometric experimental technique. Journal of Membrane Science 131 1997 95-105. 

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. 

This measurement is always determined by physical, densimetric or refractometric analysis. The expression of the results can be given according to several scales some are rarely used, i.e. degree Baume and degree Oechsle. Presently, two systems exist (Section 10.4.3) ... 

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