Refractometry refractive index

Refractometry Refractive index change for the enzyme solution is measured using a differential refractometer 0.1-5 mg ml ... 

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 ... 

Part—IV has been entirely devoted to various Optical Methods that find their legitimate recognition in the arsenal of pharmaceutical analytical techniques and have been spread over nine chapters. Refractometry (Chapter 18) deals with refractive index, refractivity, critical micelle concentration (CMC) of various important substances. Polarimetry (Chapter 19) describes optical rotation and specific optical rotation of important pharmaceutical substances. Nephelometry and turbidimetry (Chapter 20) have been treated with sufficient detail with typical examples of chloroetracyclin, sulphate and phosphate ions. Ultraviolet and absorption spectrophotometry (Chapter 21) have been discussed with adequate depth and with regard to various vital theoretical considerations, single-beam and double-beam spectrophotometers besides typical examples amoxycillin trihydrate, folic acid, glyceryl trinitrate tablets and stilbosterol. Infrared spectrophotometry (IR) (Chapter 22) essentially deals with a brief introduction of group-frequency... 

Fig. 12.4 Continuous dilution differential refractometric data for the C6H12/C6D12 isotopomer pair at 298.15 K. (a) through (d) are interferograms observed at 650, 559, 520 and 470 nm, respectively. (e) shows refractive index differences derived from the interferograms left to right 650, 559, 520 and 470 nm) and (f) is a dispersion plot of the data. In (f) the interferometric data are compared with the result at 589.3 nm obtained by Abbe refractometry, which nicely illustrates the better precision of CDDR (Reprinted from Wieczorek, S. A., Urbanczyk, A. and Van Hook. W. A., J Chem. Thermodyn. 28, 1009 (1996) copyright 1996 with permission from Elsevier)...

Differential Refractometry (dn/dc). Stock solutions of polymer were prepared with known concentrations (w/v) in the solvent of choice, and the specific refractive index increment (dn/dc) was measured at 26 deg C with a KMX-16 Laser Differential Refractometer (LDC/Milton Roy). Sample concentrations typically were ca. 5 x 10 3 gm/ml. 

Optics Refractometry, interferometry, timhidimetry, polarimetry Refraction index, interference, turbidity, rotation of polarization plane... 

Clearly, the calculation of moisture content by difference, whether using hydrometry or refractometry to obtain estimates of solute concentration, is an approximate method. Its utility depends upon there being a repeatable correlation between either density or refractive index and the true percent weight concentration of the solution. This repeatability is dependent upon the exact composition of the solute system. 

Refractometry can be used to determine the composition of a copolymer. In addition, differential refractometry has been used to study micellization in dilute block copolymer solutions (Tfizar and Kratochvfl 1972). The refractive index (n) is obtained in an Abbe refractometer via measurements of the critical angle for external reflection. The refractive index increment dn/dc, where c is the polymer concentration, can be related to the molecular weight of particles in solution. Further details of the method are provided by Pepper and Samuels (1989). 

Derivative formation (pre-column derivatisation Section 4.5) is the most widely used approach that permits detection to be accomplished. It is based on the light-absorption properties of each derivatised amino acid or peptide that emerges from the column. Alternatively, changes in refractive index (RI) of the mobile phase that occur when solutes are present in the eluate can be exploited to detect the arrival of a separated component at the end of a chromatographic column. The Rl-measur-ing detector can be quite simple, or interference-polarising refractometry can be employed, allowing capillary columns to be used, giving detection limits of about 10-7 in RI, so that about 10 pg of a polypeptide can be detected in an eluate (Alexander et al., 1992). 

These are properties, such as the pH of an aqueous solution, melting point/range, and refractive index. The procedures used for the measurement of these properties are usually unique and do not need much elaboration, for example, capillary melting point and Abbe refractometry. The tests performed in this category should be determined by the physical nature of the new drug substance and its intended use. 

The rates of change (slopes of the curves) of many important properties (such as the refractive index, surface tension, and gas permeabilities) as a function of temperature, the value of the dielectric constant, and many other optical and electrical properties, often change considerably at Tg. These changes enable the measurement of Tg by using techniques such as refractometry and dielectric relaxation spectroscopy. Refractometry provides results which are similar to those obtained from dilatometry, because of the correlation between the rates of change of the specific volume and of the refractive index with temperature. Dielectric relaxation spectroscopy is based on general physical principles which are similar to those in dynamic mechanical spectroscopy, the main difference being in its use of an electrical rather than a mechanical stimulus. 

Refractometry is another approach for direct detection of carbohydrates. An interesting holography-based refractive index detector was implemented by Burggraf et al. [207]. A cyclic channel of 80 mm in circumference and 10-p.m deep was fabricated. The detection scheme was constructed having a diode laser beam (670 nm) split into two beams, one passing through the separation... 

Refractometry is a technique used to detect the concentration of binary mixtures based on differences in their refractive index. Besides concentration, it is also a simple method to quantify purity. Salinity of brine or sucrose concentrations in grapes or syrup are two typical applications. Urine-specific gravity is measured for drug diagnostics and plasma protein is assessed by refractometry in veterinary medicine. 

Refractometry is effective for liquids with a refractive index smaller than that of flint glass and typically between 1.3 and 1.7. The accuracy is one to two units to the fourth decimal place. 

Refractometry Based on change in refractive index by the displacement of proteins... 

Refractometry is an analytical technique that characterizes structure and composition of materials by the velocity of light transmitted through them. The result of the measurement is usually expressed as the ratio of the velocity of light through a vacuum (c) to that of the sample v), and is referred to as the refractive index ... 

Table 1 shows the refractive indices for several materials. The variation of refractive index as a function of electromagnetic radiation wavelength (dispersion spectrum) provides simultaneous information about the polarizibility and absorption properties of the sample. The rapid development of modern optical and imaging technologies such as lasers and photodiode arrays creates opportunities for application of refractometry to small analytical systems and multidimensional monitoring. 

In principle, absolute values of the refractive index can be used to identify chemical species in the same fashion as boiling and melting points, and the density of light absorption properties. Specific refraction and dispersion spectra are used to characterize the chemical structure of analytes. However, it is very difficult to apply refractometry for this purpose because of small differences in refractive index between substances, and relatively large dependence of the index with temperature, dissolved gas, and impurities. This method has been used more successfully in combination with microscopy to differentiate between components of inhomogeneous solid samples. 

Refractometry Refractometry is a quick and reasonably accurate alternative to chemical analysis for serum total protein when a rapid estimate is required. The refractive index of water at 20°C is 1.330 if solute is added to the water, the refractive index of a dilute solution increases linearly and proportionally to the solute concentration at higher concentrations of dissolved solids (50-200gl ), the increase is nearly linear. Temperature affects appreciably the refractive index of a solution, so refracto-meters for clinical use compensate for temperature effects. Serum contains dissolved solids in concentrations of 80-100 gl, most of which are proteins. In the refractometry of serum, it is assumed that the concentration of inorganic electrolytes and nonprotein organic compounds does not vary appreciably from serum to serum and that the differences in the refractive index reflect primarily the differences in protein concentrations. The assumption has been shown to be reliable for clear, nonpigmented samples, but hemolysis, lipemia, icterus, and azotemia produce erroneously high results. The method cannot be used for urine protein measurement because of excess solutes in relation to the protein. 

By using the deflection principle of refractometry, it is possible to use one sample cell throughout the entire refractive index range from 1.00 to 1.75. An optical block and heat exchanger are provided to bring the liquid temperature to the temperature of the cell at all flow rates normally encountered. An example of a chromatogram obtained from this type of detector is shown in Figure 2. 

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