Molar extinction coefficient concentration

Em molar extinction coefficient (concentration in g-moles/e). EM electron microscope,... 

This is the fundamental equation of colorimetry and spectrophotometry, and is often spoken of as the Beer-Lambert Law. The value of a will clearly depend upon the method of expression of the concentration. If c is expressed in mole h 1 and / in centimetres then a is given the symbol and is called the molar absorption coefficient or molar absorptivity (formerly the molar extinction coefficient). 

An interesting change of the UV-absorbances with electrolyte concentration was observed for A18 and T18, as shown in Fig. 5. The molar extinction coefficient of A18 decreased by about 7% at 0.09 mM, and that of T18 about 10% at 0.16 mM. These concentrations may correspond to the critical micelle concentration, since the cmc observed from the surface tension measurements were about 0.1 mM for both A18 and T18. 

The reaction solution was diluted with 36 mL of water. The unreacted free drug and other low molecular weight materials were removed by a Centriprep-10 concentrator. Purification was repeated until HPLC analysis (Bio-Sil TSK-250) of the product indicated the absence of free drug. The final purified product was lyophilized to afford 483 mg of a yellow solid. This solid product was readily soluble in water or aqueous buffer. The amount of drug covalently bound to MVE was estimated by the absorbance at 303 nm using a molar extinction coefficient of 17.03 x 103. The MVE-y-hy-MTX contains 26% methotrexate-y-hydrazide by weight. 

One cm3 of the reactant/product/catalyst mixture was sampled periodically during the reaction for the transmission infrared analysis (Nicolet Magna 550 Series II infrared spectrometer with a MCT detector). The concentrations of reactants and products were obtained by multiplying integrated absorbance of each species by its molar extinction coefficient. The molar extinction coefficient was determined from the slope of a calibration curve, a plot of the peak area versus the number of moles of the reagent in the IR cell. The reaction on each catalyst was repeated and the relative error for the carbamate yield measured by IR is within 5%. 

AMCA-hydrazide has a maximal excitation wavelength of 345 nm and a maximum emission wavelength in the range of 440-460 nm. A solution of AMCA in PBS at a concentration of 16.7ng/ml (71.61 nmoles/ml) gives an absorbance at 345 nm of about 1.28. This translates into a molar extinction coefficient at this wavelength of about 13,900M em-1. Different solvents and conditions may alter this value somewhat. 

Measure the absorbance of the biotinylated protein solution at 354 nm. Use the molar extinction coefficient for the chromogenic group (e = 29,000 M-1cm-1) to determine the concentration of biotin present. To determine the molar ratio of biotin-to-protein, divide the molar concentration of biotin by the molar concentration of protein present (which may be determined by using the Coomassie assay or the BCA assay methods). 

In the pulse oximeter, the concentration and molar extinction coefficient are constant. The only variable becomes the path length, which alters as arterial blood expands the vessels in a pulsatile fashion. 

DOX concentration was determined spectrophotometrically based on the molar extinction coefficient of 125000 OD M (38) in a dual-beam spectrophotometer (either Perkin-Elmer Lambda 3B or Kontron Uvikon 860). The DOX quantification was confirmed by HPLC (49-51). Purity of DOX and its degree of degradation during the processes of liposome preparation and liposome storage were determined by a combination of HPLC and TLC, as described by Barenholz leave et al. (38,49,50). 

This amount of thiocyanate is sufficient for both complete reduction and complex formation. Reduction is allowed to proceed for 30 to 45 s after the addition of the thiocyanate. A bright red color can readily be observed at a technetium (VII) concentration of 0.1 ng per ml. Acetone (6 ml) is then added and the volume of the solution mixed and adjusted to 10 ml with distilled water. At this point, the color has generally developed to less than 50% of its final intensity. Quartz 1-cm glass-stoppered cells are filled with the technetiiun solution and placed in a 20 °C water-cooled spectrophotometer. The extinction will approach a maximum intensity in 1 to 3 h. The maximiun extinction occurs at 510 nm with a molar extinction coefficient and standard deviation of 47,500 + 500 in 60 vol. % of the acetone-aqueous medium. An additional examination of the analysis may be carried out by extract-... 

The light absorption act is fast compared with proton exchange rates and therefore the ultraviolet spectrum of a system in protonation equilibrium (1) is the superposition of the spectra of the base and the conjugate acid, each contributing according to its concentration. So the observed molar extinction coefficient is ven by (4), where a is the fraction of the base converted into the... 

Absorbance is proportional to concentration and path length (the Beer-Lambert Law). The intensity of absorption is usually expressed in terms of molar absorbance or the molar extinction coefficient (a) given by ... 

Outlined below is the exact method of calculation of quantum yields of the disappearance of compound A and the formation of the compounds Bi to B , even if only their analytical concentrations at a few time intervals are known and their molar extinction coefficients are not known (for more details see Ref. 71). 

For the initial phase of the photo-Fries rearrangement, IA can be determined approximately by subtracting the absorption due to the strongest absorbing product of the reaction mixture, provided its concentration and molar extinction coefficient are known. By means of this initial rate approach Humphrey8 determined the quantum yields of the photorearrangement of 13 (913-14 = 0.14), of 14 (914-.18 = 0.056), and of poly-2,2-propanebis(4-phenyl carbonate) ([Pg.138]

Figure 5. Plot of molar extinction coefficient against LCC (fraction C-l-A-1) concentration. (Reprinted with permission from ref. 8. Copyright 1979 Walter de Gruy-ter Co.)...

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