Optical density ratio

The denominator being a constant, a plot of the observed optical density ratio against the molar fraction of each component will be a straight line. This method has also been extended to mixtures of three substances. A further simplified form of the ratio method has been suggested48. If the optical densities of standard solutions of two substances at concentrations cx and c at wavelengths are Dx and Z), respectively, then the observed optical density of a solution containing the two components at concentrations xt and will be... 

Rate constants for methanol and ethyl alcohol relative to those for benzoate ion, phenylacetate ion and p-nitrobenzoate ion are shown in Table III. Each value in the table consists of experiments at five separate concentration ratios. The random uncertainty in each value is less than 10%. In determining these rate constants from optical density ratios it was necessary to make a small correction for the contribution to the optical density by the H-adduct free radical. The molar extinction coefficients at 340-350 m/x for the H-adduct and OH-adduct are similar for benzoic acid (22) and were assumed to be comparable for the other two aromatic ions in the table. The correction is necessary since the rate constants for the reaction of hydrogen atoms with the alcohols used are two orders of magnitude lower than the rate constants for hydrogen atom addition to the aromatic ring, while the analogous hydroxyl rate constants are roughly comparable. 

The lattice vibrations may, in addition, provide a useful information concerning the degree of crystallinity or, rather short range order. For example where tiny zeolite crystallites are formed X rays Diffraction patterns may exhibit a significant broadening which could be misleading. Examination of the optical density ratio of appropriate vibrations could lead to a more correct evaluation of the crystallinity of the zeolite (25). 

Fig. 4. Alterations in optical density ratios unrelated to cerebral glucose utilization. The influence of exposure time in the preparation of the autoradiograms upon the optical density of neocortex relative to optical density of white matter. In all cases, total in neocortex and white matter was 509 and 179 nCi/g, respectively. (Data from Kelly and McCulloch, 1981c.)...

Calculation op Optical-density Ratio, 500 mm/580 mm, for Different Mixtures OF Cysteine and Cysteinylglycine (Naphthoquinone Sulfonate Method)... 

Composition oj mixture % cysteine Optical density Ratio 500 mufSSO mu... 

In the latter case, D6.08 is the sum of the optical densities of the vinylidene and vinyl absorption bands in this region. An optical density ratio for these bands of approximately this value was found (1.75 to 3.3) for the products of thermal degradation of polypropylene. It is seen that only in the case of amorphous polypropylene irradiated with gamma-radiation from Co is the ratio (D11.23 + D10.99)/D6.08 close to the value calculated from the extinction coefficients of these bands. In the spectra of irradiated isotactic polypropylene, the intensity of the 6.08 pm band is greater than would be expected if only vibration of terminal double bonds contributes to absorption in this region. This increase in absorption in the 6.08-pm region can be related to absorption by the internal double bond in the allyl radical, the vibrational frequency of which is lowered by conjugation of the Jt-electrons of the double bond... 

Substrate concentration ratio C/C in donating solution is determined easily by using optical density ratio A/A of these solutions. As permeability value is proportional to diagram slope ratio (velocity constant k) the following formula was used for a convenient calculation of membrane permeability ... 

In dye-binding tests, milk is mixed with excess acidic dye solution where the protein binds the dye in a constant ratio and forms a precipitate. After the dye—protein interaction takes place, the mixture is centrifuged and the optical density of the supernatant is determined. Utilization of the dye is thus measured and from it the protein content determined. Several methods for appHcation of dye-binding techniques to milk are given (24,25). 

The ratio /,//0 is the fraction of the incident light transmitted by a thickness / of the medium and is termed the transmittance T. Its reciprocal /0//, is the opacity, and the absorbance A of the medium (formerly called the optical density... 

Delaire et al. [124] have reported that laser photolysis of an acidic solution (pH 2.8) containing PMAvDPA (23) and MV2 + allows the formation of surprisingly long-lived MV + - and DPA cation radicals with a very high charge escape quantum yield. The content of the DPA chromophores in PMAvDPA is as low as less than 1/1000 in the molar ratio DPA/MAA. Figure 20 shows a decay profile of the transient absorption due to MV + monitored at 610 nm [124]. The absorption persists for several milliseconds. As depicted in Fig. 20, the decay obeys second-order kinetics, which yields kb = 3.5 x 10s M 1 s. From the initial optical density measured at 610 nm, the quantum yield for charge escape was estimated to be 0.72 at 0.2 M MV2 +. ... 

Ratio of the optical density of the benzophenone triplet to that of the ketyl radical. 

Ishii and Murakami (1991) evaluated the CFB scaling relationships of Horio et al. (1989) using two cold CFB models. Solids flux, pressure drop, and optical probe measurements were used to measure a large number of hydrodynamic parameters to serve as the basis for the comparison. Fair to good similarity was obtained between the beds. Dependent hydrodynamic parameters such as the pressure drop and pressure fluctuation characteristics, cluster length and voidage, and the core diameter were compared between the two beds. The gas-to-solid density ratio was not varied between the beds. As seen in Table 7, the dimensionless solids flux decreased as the superficial velocity was increased because the solids flux was held constant. 

It is well known23 that ionization ratios / can be determined from spectra using the expression /=( > — DB)/ D — D), where D is the measured UV-vis optical density or NMR chemical shift and DA and Z>B refer to the values for the pure acid form (i.e. BH+) and pure base form (i.e. B), respectively. Recasting this in terms of D gives equation (27) ... 

The principle of this method is that the initial slope (time = zero) of the optical density-time curve is proportional to the rate of flocculation. This initial slope increases with increasing electrolyte concentration until it reaches a limiting value. The stability ratio W is defined as reciprocal ratio of the limiting initial slope to the initial slope measured at lower electrolyte concentration. A log W-log electrolyte concentration plot shows a sharp inflection at the critical coagulation concentration (W = 1), which is a measure of the stability to added electrolyte. Reerink and Overbeek (12) have shown that the value of W is determined mainly by the height of the primary repulsion maximum in the potential energy-distance curve. 

We have found the combination of the azide compound and the styrene resin is well suited for achieving high resolution and high aspect ratio patterns using KrF excimer laser stepper system, because of the absence of swelling-induced pattern deformation during alkaline development and the suitable optical density at 248 nm in terms of sensitivity. 

Figure 4. Ratios of optical densities at 1730 cm1 (linear oligomers)/1705 cm"1 (cyclic dimers) as a function of mole fraction of acrylic acid in various solvents (1) dioxane (2) methanol (3) acetic acid (4) chloroform (5) toluene (6) CClk (4).

Figure 5. Ratios of optical densities at 1730 cm 1/1705 cm1 plotted in Arrhenius coordinates for pure acrylic acid (100) and acrylic acid solutions in toluene at 90, 80, and 60 volume per cent of monomer (5).

The presence of conjugated double-bond systems in the purine and pyrimidine bases means that DNA and RNA absorb light in the ultraviolet region at 260 nm. For approximate determinations it can be assumed that a 50 /xg ml-1 solution of double-stranded DNA (dsDNA) has an absorbance of 1 at 260 nm. More exact quantitation can be obtained by comparing the ratio of the absorbance of the sample at 260 and 280 nm. The term optical density (OD) is often used in place of absorbance. Pure DNA preparations should have an OD 260/OD 280 of 1.8. Ratios less than this may indicate protein contamination while higher ratios may indicate the presence of RNA. 

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