Determination Of Molar Absorption Coefficient Research Articles

Direct determination of molar absorption coefficients of several molecules in the lowest excited singlet states.

Molar absorption coefficient of the lowest excited state is an indispensable information for the quantitative investigation of photochemical reactions by means of transient absorption spectroscopy. In the present work, we quantitatively estimated the molar absorption coefficients of the S1 state of the solute in three solution systems, Rhodamine B in ethanol, ZnTPP in DMF and N,N'-bis(2,6-diisopropylphenyl)terrylene-3,4,11,12-tetracarboxydiimide (TDI) in chloroform, by perfectly bleaching the ground state molecules using the picosecond 532-nm laser pulse with a large number of photons. These solution systems were selected because no obvious photodegradation was detected in the present range of the excitation intensity. The molar absorption coefficient obtained by this method was verified by the numerical analysis of the excitation intensity dependence of the transient absorbance by taking into account the inner filter effect (absorption of the excitation light by the S1 state produced by the leading part of the pump pulse) and the decrease of the ground state molecules by the pump process (depletion). In addition, these molar absorption coefficients were confirmed by the comparison of relations between the excitation intensity and the transient absorbance of the S1 state under the condition where the fraction of the excited solute is ≪ 10% by the femtosecond pulsed laser excitation. From these results, the error of the molar absorption coefficients was estimated to be < 5%. These values can be used as reference ones for the estimation of molar absorption coefficients of other systems leading to the quantitative elucidation of the photochemical reactions detected by the transient absorption spectroscopy.

Alizarin Red S as a colored agent for the extraction-photometric and color measurement determination of some local anesthetic organic compounds

The possibility has been considered for using 1,2-dihydroxyantraquinonone-3-sulfoacid (Alizarin Red S, ARS) as a colored agent for the determination of organic bases as of their ion associates. Spectrophotometric and colorimetric properties of the ion associates of cetyltrimethylammonium bromide and local anesthetics Novocaine and Lidocaine with ARS have been studied in aqueous solutions at pH 2–6; the optimal conditions for the formation of ion associates have been determined and the extraction mechanism has been revealed. Calibration curve equations have been obtained for the dependences of the absorbance of extracts and back extracts of organic bases in aqueous and organic phases, as well as the chromaticity functions (CF) of the ion associates on the concentration of the organic bases in aqueous and organic phases. Molar absorption coefficients and CF of the considered ion associates have been determined. The advantages of the color measurement over spectrophotometry for the determination of molar absorption coefficients and CF have been demonstrated. An application of the developed procedure has been proposed.

Determination of molar absorption coefficients of organic compounds adsorbed in porous media

The kinetics of direct photochemical transformations of organic compounds in light absorbing and scattering media has been sparsely investigated. This is mostly due to the experimental difficulties to assess the major parameters: light intensity in porous media, the reaction quantum yield and the molar absorption coefficient of the adsorbed compound, ε i ( λ). Here, we propose a method for the determination of the molar absorption coefficient of compounds adsorbed to air-dry surfaces using the Kubelka–Munk model for the description of radiative transfer. To illustrate the method, the molar absorption coefficients of three compounds, i.e. 4-nitroanisole (PNA), the herbicide trifluralin and the flame retardant decabromodiphenyl ether (DecaBDE), were determined on air-dry kaolinite. The measured diffuse reflectance spectra were evaluated with the Kubelka–Munk model and with previously determined Kubelka–Munk absorption and scattering coefficients ( k and s), for kaolinite. For all compounds the maximum absorption band was found to be red shifted and the corresponding ε i ( λ) values were significantly greater than those determined in solvents. Together with the absorption and scattering coefficient of the medium, the measured ε i ( λ) can be used to determine the quantum yield of the photochemical reaction in this medium from experimentally determined reaction kinetics.

Nature of Surface Sulfate Species and the Generation of Active Sites on Silica−Zirconia Mixed-Oxide Catalysts

Two series of sulfated silica−zirconia mixed oxides have been prepared and the densities of both Brønsted and Lewis acid sites calculated. Catalytic activity data were obtained for two Brønsted acid catalyzed reactions, the alkylation of toluene by styrene in the liquid phase and but-1-ene double bond isomerization in the gas phase, but no correlation could be obtained between activity and the number of Brønsted acid sites available. Using ab initio calculations for the sulfate structures and the determination of molar absorption coefficients for adsorbed pyridine which was used as a probe for both types of acid site, an understanding of the evolution of acid site densities as a function of sulfate loading has been established. Using this information, it is proposed that the active site for these reactions, which both involve a step involving protonation of the CC group, must involve an adjacent Brønsted and Lewis acid site pair where the latter acts to initially adsorb the vinyl group prior to protonation.

Spectrophotometric analysis of sodium fluorescein aqueous solutions. Determination of molar absorption coefficient

The usefulness of sodium fluorescein (SF) and related physical parameters were analysed. Two factors that may affect the molar absorption coefficient (epsilon) of this compound were the presence of impurities and the pH of the solution. As discrepant values can be found in the literature for that coefficient, a purification technique was used and SF quantification was performed according to sodium concentration determined by atomic absorption spectrophotometry. The molar absorption coefficient of the SF solution in phosphate buffer pH 7.4 was determined. To study the influence of pH on epsilon determination, absorption spectra at pH1, 3, 5, and 10 were also analysed.

The determination of molar absorption coefficients of metastable states

A computer controlled spectrophotometer is described which allows spectroscopic and kinetic measurements on a sample which is simultaneously irradiated with strong monochromatic light. Data gathering routines and methods to calculate the molar absorption coefficients of metastable species are discussed. The triplet—triplet absorption spectrum of fluorenacene is reported.