Refractometry, differential

In order to determine molecular weight by light scattering, the refractive index Hq of the solvent and the refractive index increment dn/dc) for the solution at a constant temperature must be known. The former is readily measured with a simple laboratory refractometer such as the Abbe type. Determination of dnjdc) of the solution with high accuracy can be achieved by using two types of refractometers divided-cell differential refractometers and interferometers. 

The difference between refractive indices of the solution ( ) and the solvent (no). An (=n - no), is calculated by the relation  

Where/is the focal length of the microscope and 0 is the angle between the thin diagonal glass partition and the lateral face of the cell. The refractive-index increment of the solution is obtained as the initial slope of the plot of A versus c for solutions with various polymer concentrations. Brice-type differential refractometers are marketed by Otsuka Electronics Co. (type DRM-1020) and C. N. Wood Co. (type RF-600). 

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

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 ... 

Table 12.3 CDDR (continuous dilution differential refractometry) least squares parameters, molar volume isotope effects, and derived PIEs for some isotopomer solutions at 298.15K see Equation 12.15, AR/R = A + mv2 (Wieczorek, S. A., Urbanczyk, A. and Van Hook, W. A.,. /. Chem. Thermodyn. 28, 1009 (1996)) ...

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. 

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. 

Thus, in small-angle x-ray scattering, measurement of the molecular weight of a macromolecule in concentrated solvent requires knowledge of the preferential interaction parameter. This can be measured by techniques such as differential refractometry, densimetry, and isopiestic vapor phase equilibrium measurements. For densimetry,... 

Lactoglobulin A in 40% 2-Chloroethanol. Previous light scattering and differential refractometry measurements (8, 23) have shown that / -lactoglobulin exhibits strong preferential interactions with solvent components in the water-2-chloroethanol system. Since the preferential interaction between protein and 2-chloroethanol in this system was found to be maximal at 40% (v/v), the effect of this interaction on the partial specific volume of the protein was determined. 

Triglycerides in vegetable oils are separated according to their equivalent carbon number by reversed-phase liquid chromatography and detected by differential refractometry. Quantitation is by area normalization. Elution order is determined by calculating the equivalent carbon numbers, ECNs, often defined (as we said before) as CN — 2n, where CN is the carbon number and n is the number of double bonds. To calculate ECNs more accurately, the origin of the double bond is taken into account ... 

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). 

Abbreviations DR, differential refractometry SLS, static light scattering DLS, dynamic light scattering SAXS, small-angle X-ray scattering TEM. transmission electron microscopy. 

Micellization of PS-PMA diblock and triblock copolymers in 80 20 dioxane water mixtures was investigated by Qin et al. (1994) using static and quasi-elastic light scattering, differential refractometry, viscomelry, sedimentation... 

For compounds bearing acrylate or methacrylate groups, the copolymer compositions were almost the same as the monomer feed compositions, and the molecular weights were nearly identical to that of poly(methyl methacrylate) (PMMA) synthesized as a control under the same reaction conditions. In addition, the dye-bearing repeat units were present uniformly in all molecular weights, as seen by comparing GPC molecular weight distribution curves determined by differential refractometry and by visible absorbance detection at the X of the... 

The ratio on the left-hand side can be obtained as a function of M since fw,app(M) / Mw can be determined, as described above, from experimental information. Thus, Eq. (5.7) allows determination of wa(M), the chain composition distribution when all other parameters on its right-and side are measured by differential refractometry. Once wa(M) is known, we are ready to compute v(M) from Eq. (5.3), fw(M) from Eq. (5.6), and finally Mw [59]. 

The preferential adsorption in dilute solution of poly(phenyl methacrylate) and its derivatives in tetrahydrofuran/water mixtures has been studied by differential refractometry and dialysis equilibrium [108], Relationships were found between the rigidity [Pg.32]

Extensive molecular characterization studies of the arms and the final products by MO and SLS and compositional characterization studies by XH NMR, UV-SEC and differential refractometry lead to the conclusion that the copolymers are characterized by a high degree of molecular and compositional homogeneity. 

The quantity 3uref/3cwt is routinely measured by differential refractometry and light scattering by nonabsorbing protein solutions. It varies slightly, from 1.7 to 2.0 x ICR4 liters/g.8... 

Present emphasis is being placed on the use of detector combinations in fact, the triple-detection system , SEC-light-scattering-vis-cometry-differential refractometry, is being used more frequently, sometimes with the addition of an on-line UV detector to monitor composition (20). 

Trudelle and Nicolas (24) utilized light reflection, differential refractometry and densitometry to find that the skin of Integral CA membranes had a water content of 38 percent by weight whereas the substructure contained 61.8 percent. The water content... 

The samples prepared by this chlorosilane route are characterized by high degrees of molecular and compositional homogeneities, as was confirmed by the exhaustive characterization data provided by SEC, membrane osmometry, low angle laser light scattering, differential refractometry, vapor pressure osmometry, UV-SEC, and NMR. The most important feature of the method is that every step of the reaction is monitored by taking small aliquots from the reaction mixture. 

The continuous detectors most often used in liquid chromatography are based on ultraviolet or visible absorption, fluorescence, and differential refractometry. 

Studies on Dilute Solutions. The procedures and instrumentation for differential refractometry light scattering, viscomet-ry and solution dialysis are those given by Tanner and Berry. 

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