Molar absorption coefficient determination

As the number of substituents increases, molar absorption coefficients determined in the maxima of the characteristic fullerene absorption bands decrease exponentially (Fig. 1.4). The maximum decrease in the extinction coefficient is observed in transiting from Cg to mono- and di-substituted products, slightly changing at > 3. 

The basic principle of most colorimetric measurements consists in comparing under well-defined conditions the colour produced by the substance in unknown amount with the same colour produced by a known amount of the material being determined. The quantitative comparison of these two solutions may, in general, be carried out by one or more of six methods. It is not essential to prepare a series of standards with the spectrophotometer the molar absorption coefficient can be calculated from one measurement of the absorbance or... 

If it is known that the compound obeys Beer s Law the molar absorption coefficient e can be determined from one measurement of the absorbance of a... 

Procedure, (a) Determination of molar absorption coefficients and verification of additivity of absorbances. The molar absorption coefficients must be determined for the particular set of cells and the spectrophotometer employed. For the present purpose we may write ... 

A) The use of a calibration graph. This overcomes any problems created due to non-linear absorbance/concentration features and means that any unknown concentration run under the same conditions as the series of standards can be determined directly from the graph. The procedure requires that all standards and samples are measured in the same fixed-path-length cell, although the dimensions of the cell and the molar absorption coefficient for the chosen absorption band are not needed as these are constant throughout all the measurements. 

Hendriksen, B. A. Sanchez-Felix, M. V. Tam, K. Y., A new multiwavelength spectrophotometric method for the determination of the molar absorption coefficients of ionizable drugs, Spectrosc. Lett. 35, 9-19 (2002). 

Determine the lowest energy transition of a simple organic molecule from the molar absorption coefficient and the structural formula. 

In order to determine the molar absorption coefficient, a pure, dry sample of the compound must be available. Purity is often difficult to check in a routine analytical laboratory but dryness may be achieved by desiccation. Care must be exercised in the choice of desiccant and the temperature used, owing to the potential instability of the compound at even ambient temperatures or the effect of light. It is advisable to determine the value for the coefficient using different samples of the compound and subsequently compare the results. 

Procedure 2.1 Determination of tile molar absorption coefficient of NADH at 340 nm... 

The molar absorption coefficient of the coloured product can be used in the quantitation of individual amino acids but this value varies from one amino acid to another and must be determined under the conditions of the assay. An accepted value, however, must be used in the quantitation of the total amino acids in a mixture when absorbance readings are normally taken at 570 nm. 

A spectrophotometer which allows spectroscopic and kinetic measurements to be made on a light irradiated sample has been developed by Ranalder et al. 5). The instrument is completely controlled by a small PDP-8/I computer. Great flexibility is introduced through software control. Several data collection routines have been written, and methods for determining molar absorption coefficients of metastable states have been discussed. 

In a pulse-radiolysis optical-absorption method, the value of kje, where 8 is a molar absorption coefficient, is measured by the time-resolved measurement of the optical absorption of solvated electrons, and then the kr value is determined by the observed value of kr/s and the value of s known separately. 

A number of dithiolato-metal-dye complexes were synthesized117 by adding thionine (TH), tolusafranine (SAF) or methylene blue (MB) to a mixture of a metal salt and Na2(mnt) or H2(tdt). The composition of the products was determined from elemental analyses and valence state considerations. Peculiar stoichiometries were found, e.g. Mn2(mnt)5(SAF)6(OH)2 11H20, necessitating the assumption that equally unusual structures existed. Nonetheless, the molar absorption coefficients of the maximum absorption were larger for the complexes than the free dyes. In hexa-methylphosphoramide, the metal dithiolene accelerated the rate of photochemical reduction versus the free ligand with TH but retarded the rate for the SAF and MB complexes. 

As was stressed above, in case of direct excitation of the lanthanides, the differences in the absorption spectra between the solvated ion and the complex formed are usually considered as slight but allow nevertheless the use of spectrophotometry for speciation purposes (for a recent example, see Giroux et al. (2000)). In the case of U(VI), the absorption changes observed upon complexation have often been used to determine equilibrium constants (for the classical example of U(VI) hydrolysed species, see Dai et al. (1998), Meinrath (1998)). For curium, no information of this kind is available the low molar absorption coefficient implies the use of solutions with high total curium concentrations, which are almost impossible to handle nowadays due to safety reasons. The absorption spectra of curium are known only for aqueous solutions of HCIO4 (Carnall et al., 1958), HC1, H2SO4 and HNO3 (Pascal, 1962). 

Both the absolute quantum yield (determined with respect to zinc tctraphcny 1 porphvrin in ethanol) and the product of the molar absorption coefficient at the excitation wavelength with the quantum yield, e Q, which represents the overall luminescence efficiency follow the... 

NCs is indispensable. In the case of cadmium chalcogenide NCs, the concentration of a colloidal solution can be determined in good approximation by means of UV-vis absorption spectroscopy thanks to tabulated relationships between the excitonic peak, the NC size, and the molar absorption coefficient.96 An advanced approach for shell growth derived from chemical bath deposition techniques and aiming at the precise control of the shell thickness is the so-called SILAR (successive ion layer adsorption and reaction) method.97 It is based on the formation of one monolayer at a time by alternating the injections of cationic and anionic precursors and has been applied first for the synthesis of CdSe/CdS CS NCs. Monodispersity of the samples was maintained for CdS shell thicknesses of up to five monolayers on 3.5 nm core CdSe NCs, as reflected by the narrow PL linewidths obtained in the range of 23 to 26 nm FWHM. 

Because the molar absorption coefficients of absorbing species in catalyst materials are usually not known, a calibration needs to be performed to relate intensity (at a certain wavelength or an integral over a range) to concentration. In a best-case scenario, the concentration is measured by a second independent method applied simultaneously. Published attempts include the use of EPR spectroscopy for the determination of the concentration of V4+ in VO /support materials in this case, the EPR tube was a "side-arm connected to the UV-vis cell, and samples could be transferred without exposure to air (Catana et al., 1998). EPR intensity and UV-vis intensity (KM function at a particular wavelength) were linearly correlated with each other. 

A stock solution of MDA is prepared as described previously, by dilution of 1 mmol to 100 ml with sulphuric acid (1% v/v). The concentration of MDA is determined by UV-spectrophotometry assuming a molar absorption coefficient of 13700 M-1 cm-1 at 245 nm. This solution is then diluted in 0.1 M Tris buffer (pH 7.0) and brought to... 

A standard solution of albumin (bovine serum) of concentration 4 mg/ml. Define the concentration accurately by diluting in water to give A279 of 0.140, corresponding to a concentration of 200 fig/ ml (determined from the molar absorption coefficient at 279 nm for albumin in aqueous solution of 45 000). Dilute this solution 1 4 to give a final concentration of 50 fig/m. ... 

Standard curve A series of dilutions of bovine serum albumin in water are prepared containing between 0 and 100 pig protein in 1 ml volume and the assay is performed as described above on each dilution. The exact concentration of the bovine serum albumin stock solution is determined using the molar absorption coefficient of 45 000 for bovine serum albumin at 279 nm after diluting to approximately 0.2 mg/ml. 

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