Refractive Concentrators

When a slight amount of salt is present, it forms a colloidal solution, containing rod-shaped particles. The solution shows streaming double refraction. Concentrated solutions may gel and a paste of the dye with water is typically plastic. 

Note that in liquid phase chromatography there are no detectors that are both sensitive and universal, that is, which respond linearly to solute concentration regardless of its chemical nature. In fact, the refractometer detects all solutes but it is not very sensitive its response depends evidently on the difference in refractive indices between solvent and solute whereas absorption and UV fluorescence methods respond only to aromatics, an advantage in numerous applications. Unfortunately, their coefficient of response (in ultraviolet, absorptivity is the term used) is highly variable among individual components. 

Figure I represents a two-dimensional damage distribution of an impact in a 0/90° CFRP laminate of 3 mm thickness. Unlike in ultrasonic testing, which is usually the standard method for this problem, there is no shadowing effect on the successive layers by delamination echos. With the method of X-ray refraction the exact concentration of debonded fibers can be calculated for each position averaged over the wall thickness. Additionally the refraction allows the selection of the fiber orientation. The presented X-ray refraction topograph detects selectively debonded fibers of the 90° direction.

Chakactkrisation of Unsaturatkd Aliphatic Hydrocarbons Unlike the saturated hydrocarbons, unsaturated aliphatic hydrocarbons are soluble in concentrated sulphuric acid and exhibit characteristic reactions with dUute potassium permanganate solution and with bromine. Nevertheless, no satisfactory derivatives have yet been developed for these hydrocarbons, and their characterisation must therefore be based upon a determination of their physical properties (boiling point, density and refractive index). The physical properties of a number of selected unsaturated hydrocarbons are collected in Table 111,11. 

Fundamental Limitations to Beers Law Beer s law is a limiting law that is valid only for low concentrations of analyte. There are two contributions to this fundamental limitation to Beer s law. At higher concentrations the individual particles of analyte no longer behave independently of one another. The resulting interaction between particles of analyte may change the value of 8. A second contribution is that the absorptivity, a, and molar absorptivity, 8, depend on the sample s refractive index. Since the refractive index varies with the analyte s concentration, the values of a and 8 will change. For sufficiently low concentrations of analyte, the refractive index remains essentially constant, and the calibration curve is linear. 

Numerous methods for the deterrnination of monomer purity, including procedures for the deterrnination of saponification equivalent and bromine number, specific gravity, refractive index, and color, are available from manufacturers (68—70). Concentrations of minor components are deterrnined by iodimetry or colorimetry for HQ or MEHQ, by the Kad-Eisher method for water, and by turbidity measurements for trace amounts of polymer. 

Density and refractive index are nearly linear functions of formaldehyde and methanol concentration. Based on available data (16—19), the density may be expressed ia g/cm by the following approximation ... 

The concentration of distilled glycerol is easily determined from its specific gravity (15) by the pycnometer method (16) with a precision of 0.02%. Deterrnination of the refractive index also is employed (but not as widely) to measure glycerol concentration to 0.1% (17). 

Physical Properties. Almost all Hquid diacyl peroxides (20) and concentrated solutions of the soHd compounds are unstable to normal ambient temperature storage many must be stored well below 0°C. Most of the soHd compounds are stable at ca 20°C but many are shock-sensitive (187). Other physical constants and properties have been reviewed (187,188). The melting poiats and refractive iadexes of some acyl peroxides are Hsted ia Tables 10-12. 

Refractive Index. The effect of mol wt (1400-4000) on the refractive index (RI) increment of PPG in ben2ene has been measured (167). The RI increments of polyglycols containing aUphatic ether moieties are negative drj/dc (mL/g) = —0.055. A plot of RI vs 1/Af is linear and approaches the value for PO itself (109). The RI, density, and viscosity of PPG—salt complexes, which maybe useful as polymer electrolytes in batteries and fuel cells have been measured (168). The variation of RI with temperature and salt concentration was measured for complexes formed with PPG and some sodium and lithium salts. Generally, the RI decreases with temperature, with the rate of change increasing as the concentration increases. 

The concentration of a pure sugar solution is determined by measurements of polarization (optical rotation), refractive index, and density. 

ICUMSA (1) has adopted tables showing the relationship between the concentration of aqueous solutions of pure sucrose, glucose, fmctose, and invert sugar and refractive index at 20.0°C and 589 nm. 

Equations have been developed that determine the relationship of the refractive index of sucrose solutions between 0—85% concentration, 18—40°C, and 546—589 nm. 

The index of refraction of sulfuric acid solutions (62) and additional related data (66), along with solubiUty data for oxygen in sulfuric acid solutions (67), are available in the Hterature. The solubiUty of sulfur dioxide in concentrated sulfuric acid is shown in Figure 9 (68) additional data are also available (69). 

Critical Micelle Concentration. The rate at which the properties of surfactant solutions vary with concentration changes at the concentration where micelle formation starts. Surface and interfacial tension, equivalent conductance (50), dye solubilization (51), iodine solubilization (52), and refractive index (53) are properties commonly used as the basis for methods of CMC determination. 

Another classification of detector is the bulk-property detector, one that measures a change in some overall property of the system of mobile phase plus sample. The most commonly used bulk-property detector is the refractive-index (RI) detector. The RI detector, the closest thing to a universal detector in lc, monitors the difference between the refractive index of the effluent from the column and pure solvent. These detectors are not very good for detection of materials at low concentrations. Moreover, they are sensitive to fluctuations in temperature. 

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