Specific extinction coefficient

The direct absorbance methods require only a protein-specific extinction coefficient to deliver an accurate protein concentration. These methods typically require minutes to perform and require only a spectrophotometer and a good quantitative... 

Hubert Tschamler They were derived either from mean values observed for model compounds of known structure or from the properties of solvent extracts of coals. In the latter case an accurate value for %H i can be derived by measuring proton spin resonance in solution and this, combined with the optical densities observed in the infrared spectra, gives the specific extinction coefficients. (See J. F. M. Oth, E. de Ruiter and H. Tschamler, Brennstoff-Chem. 42, 378 (1961) also Ref. 7). 

The ultraviolet spectra of coals, examined as suspensions in potassium bromide, show an absorption band at 2650 A that becomes more pronounced with increasing rank of the coal. This band has been assigned to aromatic nuclei, and on the basis of data obtained from comparison between the specific extinction coefficients of coal and those of standard condensed aromatic compounds, it has been concluded that the concentration of aromatic systems in coal is lower than had previously been believed. 

Mulholland, G. and Croarkin, C., Specific extinction coefficient of flame generated smoke. Fire and Materials 2000, 24, 227-230. 

Owing to the UV absorbance of ferulic acid, steryl ferulates (SFs) can be analyzed from oils and total lipid extracts using UV-spectropho-tometric methods. These methods are robust and easy to perform, and provide a good estimate of the total content of SFs in a sample. The absorption maximum varies between different solvents, being 314nm, 327 nm, and 328 nm in heptane, isopropanol, and methanol, respectively (Evershed et ah, 1988 Seetharamaiah and Prabhakar, 1989 Bucci et ah, 2003). Further, the specific extinction coefficients for quantification of SFs are 358.9 cm in hexane (314nm, 25 °C) and 19,500 L mol cm (328 nm) (Evershed et ah, 1988 Seetharamaiah and Prabhakar, 1989). 

When concentration is expressed in g/100 ml, k is described as the specific absorbance and given the symbol A cm or A(l%, 1 cm), defined as The absorbance of a 1% w/v solution in a cell of 1 cm path-length . It is usually written in the shortened form Ai and is widely used in analytical chemistry. It was formerly known as the specific extinction coefficient , symbol or E (1%, 1 cm). American convention recognises the constant k as absorptivity (a, litre/g/cm) defined as the absorbance of a 1 g/litre solution in a cell of 1 cm path-length . These terms for absorptivity can be readily inter-converted, as follows... 

Spantin, 943 Sparine, 931 Sparteine, 972 in sport, 99 Spasmaverine, 332 Spasmoban, 535 Spasmocyclon, 496 Spasmolysin, 943 Spasmolytine, 320 Spasmonal, 332 Spasuret, 619 Specific absorbance, 223 Specific extinction coefficient, 223 Specilline G, 390 SpectraBAN 4, 847 Spectrobid, 369... 

Equations (4-10) and (4-11) can also be expressed in terms of specific extinction coefficients using the suspension optical thickness, , tlmough the following relationship. 

The catalyst concentration required to allow 0.2% transmission of the incident radiative flux can be calculated using the effective specific extinction coefficients (aj catP the reactor optical thickness ( ), and Equation (4-27) as follows,... 

Values of catalyst concentration for 0.2% transmittance are included in the last column of Table 4.4. It can be noticed that the effective specific extinction coefficients range from 2.6 10 cm g for the Rutile 1 catalyst to 1.32 lO cm g for Degussa P25, with the photocatalysts with higher extinction coefficients requiring lower catalyst concentrations to reach the condition of 0.2% of qac o.z.tk-, Thus, it can be infeired that the type of catalyst used significantly affects the concentration needed to achieve the condition 0.2% of qac h,z. t c, ... 

Figure 4.34 reports the evolution of the averaged specific extinction coefficients with elapsed time after sonication for several Ti02 catalysts. As it can be noticed, Ucaiit)... 

FIGURE 4.34. Evolution of the averaged effective specific extinction coefficients for several Ti02 catalysts (o) Degussa P2.5, (A) Hombikat UV-100, and (x) Rutile 1. 

The concentration of tFdx is detemiined by measuring the absorbance at 390nm. The corresponding molar extinction coefficient 6390 is 17,400 Af cm , as determined by correlating the absorption of tFdx with a quantitative amino acid analysis of the same probe. With a molecular mass of 6565 Da, this corresponds to a specific extinction coefficient A390 = 2.65 cm mg". ... 

Calculate the protein concentration at each wavelength using the specific extinction coefficients (for the fluorescent protein usually on the same Web page) andfor280 nm ad/toe calculated coefficients can be obtainedat http // web.expasy.org/protparam/. The ratio cone, fluorescent protein at wave-length/conc. protein 280 nm should be near 1 for the highest purity. 

Figure 10.10 Wavelength dependence of the specific extinction coefficient for various polystyrene...

In 1941, Mackinney (1) published specific extinction coefficients (a g/l /cm" ) for chlorophylls (Chls) a and b dissolved in 80% aqueous acetone. Also in 1941, Arnon (2) used these coefficients to derive his now-famous simultaneous equations for solving Chi a and b concentrations in the same solvent. Many workers (3-6) have since shown that Mackinney s coefficients were low, especially those of Chi b, and published more accurate equations but there has been a reluctance to use them probably because no conversion factors were provided to correct older data researchers seemed reluctant to change if unable to compare new data with older results. 

This is derived from the definitions of e and E A table listing the specific extinction coefficients for a large number of carotenoids can be found... 

Can you solve the problem in a different way (Hint After having determined A for the unknown try determining the specific extinction coefficient). 

---