Methanol, molar absorptivity

The spectrum exhibits maxima at 281 and 223 nm with molar absorptivities of 4,768 and 14,400, respectively. When aqueous potassium hydroxide is added to the methanolic solution of dobutamine hydrochloride the maxima at 281 and 223 shift to 293 (e=6,100) and 240 nm, respectively. These shifts are reversible by addition of hydrochloric acid. When the absorption spectrum of the drug is recorded in water rather than methanol, slight shifts in peak positions and intensities are observed ... 

Mixing methanolic samples with 2 ml methanolic 0.5% p-dimetyyla-mino benzaldehyde and 2 ml sulfuric acid with cooling and agitation, dilution to 10 ml with methanol and absorbance measurement at 420 nm within 20 min. Beer s law was obeyed from 0.5-5, 4-20, and 12.5-125 ng/ml of omeprazole, for the three methods, respectively, and the corresponding molar absorptivities (e) were 42,800,6400, and 2380. The relative standard derivations (n = 6) were 0.29-0.41% and recoveries were 98.17-100.1%. 

UV absorption spectra of spironolactone were recorded using a Shimadzu UV-VIS spectrophotometer, model 1601 PC. Spectra were obtained in methanol, 0.1M HC1, and 0.1M NaOH, and these are shown in Figure 4. The values of Ai /0>icm, and the molar absorptivity values at their corresponding Xmax are shown in the following table ... 

The a,ft unsaturated carbonyls exhibit an ultraviolet absorbance with an intense maximum in the range 220 nm and a weak one at 280 nm, depending on the polarity of their solvent (hexane 215 nm, methanol 221 nm, water 224 nm) (Fig. 5.5). This characteristic has been extensively exploited for the characterization of 4-hydroxynonenal produced during the peroxidation of hepatic tissues. Table 5.1 lists the molar absorption co-efficients for free hydroxyalkenals (average e= 10000-14000 M- cm-1 (Esterbauer and Weger, 1967). 

Standardization The molar absorption coefficient of hydroxyalkenals in water and ethanol or methanol is 13 750 at 223 nm and 13 100 at 221 nm, respectively (Esterbauer, 1982). Calibration curves of peak height versus concentration are linear in the range 0.1-500 /iM. 

After the separation of carbonyl dinitrophenylhydrazones into classes or into polar and non-polar fractions, the samples can be re-dissolved in a small volume of methanol and the amount present calculated approximately from the absorbance maxima at 365-370 nm using an average molar absorption coefficient of 26000 (Esterbauer, 1982). Alternatively, the amount of carbonyls within individual classes can be calculated from the molar absorptivities shown in Table 5.1. 

The ultraviolet absorption spectra of gemifloxacin mesylate were recorded on A Shimadzu UV-1601 PC double beam spectrophotometer with matched 1-cm quartz cells in water, methanol, 0.1 N hydrochloric acid, and 0.1 N sodium hydroxide solutions. Figure 4.1 shows the recorded absorption spectra of these solutions. The recorded spectra were essentially identical and exhibiting two peak maxima for each spectrum at 266 and 340, 272 and 342,272 and 344, and 262 and 342 nm for the solutions in water, methanol, 0.1 N hydrochloric acid and 0.1 N sodium hydroxide, respectively. The molar absorptivity of gemifloxacin mesylate was found to be moderately affected by the solvent used. The calculated molar absorptivity in water, methanol, 0.1 N hydrochloric acid, and 0.1 N sodium hydroxide solutions at the two maxima was tabulated in Table 4.1. However, the position of the maxima, as compared to water, was slightly red shifted for methanol and 0.1 N hydrochloric acid solutions and slightly blue shifted for 0.1 N sodium hydroxide solution. 

FIGURE 5. Absorption spectra of zone-refined SAA in ethanol (1) and methyl cyclohexane (2)25 the formation of tautomers is disregarded in the calculation of the molar absorption coefficient (e) curve 3 N(2-methoxy benzylidinejani1ine in methanol 2. 

The ultraviolet spectrum of methocarbamol in methanol has been reported14 Xmax 275 nm (El %, 1cm = 101). UV spectra have been recorded23 in a variety of solvents [strongest absorption maxima (nm) are underlined] 0.1N HCI (222. 272, 279s) 0.1N NaOH (222. 272) ethanol (224. 274, 280s). The molar absorptivities (brackets) in ethanol solutions have also... 

In a previous study, the amount of acid produced from 125 mJ/cm exposure of the resist film was determined (5). The value was 5 x 10- moles/cm. If the amount of ether produced per acid during a standard hot-plate PEB could be determined, it would be possible to determine how many cycles the acid reacted before it created the required differential solubility. Although the formation of the ether peak could be monitored with FTIR at 988 cm- the molar absorptivity of the peak was not known. However, the ether IR peak height can be calibrated by measuring the methanol produced by GC and relating the IR absorbance on the same wafer. Figure 3 shows a plot of FTIR peak height at 988 cm vs. methanol concentration produced from the film. One me anol is produced for each ether... 

For 2,5-dimethyl-2,4-hexadiene dissolved in methanol the molar absorptivity at the wavelength of maximum absorbanc e (242.5 run) is 13,100 M cm In the chemical literature this would be reported as... 

Ethyl acetate/methanol and ethyl acetate/hexane mixtures were the binary solvents used in this investigation. The effect of some one-component solvents was also studied using the position of the absorption maximum of the colored merocyanine form of a low-molecular weight model AcSP. For these solvents, a correlation was found between the Dimroth parameter 739 and the energy E CSP) of the absorption maximum of the merocyanine form of the low-molecular compound AcSP. In general, as the polarity of the solvent is increased, the visible absorption maximum of the merocyanines shifts to a shorter wavelength, the molar absorption coefficient decreases, and the half-width of the band increase. ... 

Two chlorophenoxyacetic acids, 2,4-D and dicamba, were extracted from soil and water and analyzed on a C g column (A = 236nm) using a 50/50 methanol/water (1% acetic acid) mobile phase [201,202], Detection limits of 0.1 pg/g in soil or l.Opg/mL in water were reported. In a similar fashion, eight chlorophenoxyacid residues (e.g., mecoprop, 2,4-D, dichlorprop, fenoprop) were extracted from water samples and analyzed on a C g column (A = 228nm) using a 60/40 methanol/water (30 mM phosphate buffer at pH 3.0) mobile phase [203]. The authors noted that 0.05% trifluoroacetic acid (TFA) used in place of the phosphate buffer as the mobile phase modifier was just as effective and produced significantly different retention times for the analytes. Molar absorptivities were tabulated for the analytes at 205 nm, 228 nm, and 280 nm. Detection limits of 0.5-2 pg/L were reported. 

Eleven phenolic acids present in olive oils (e.g., tyrosol, hydroxytyrosol, vanillic acid, syringic acid, caffeic acid, o- and j-coumaric acid, -hydroxybenzoic acid) were studied using a C g column and a 70-min 6/94 -y 100/0 methanol/water (3% acetic acid) gradient [283]. Acetonitrile adversely affected chromatographic performance and required lengthy re-equilibration times between injections. Molar absorptivities are tabulated for all compounds and detection limits ranged from I to 6 ng injected (analyte dependent). 

The molar absorptivity of 2,5-dimethyl-2,4-hexadiene in methanol is 13,100 M cm . What concentration of this diene in methanol is required to give an absorbance of 1.6 Assume a light path of 1.00 cm. Calculate concentration in these units. 

Non-polar solvents, such as hexane and benzene, produce high yields of excited states via ion recombination, and relatively low yields of radical ions. In contrast, polar solvents like methanol, acetonitrile and water support high yields of radical ions with low excited state yields, due to solvation and stabilisation of the initial ions, particularly the electrons, leading to a slow rate of ion recombination. In intermediate polarity solvents, such as acetone, approximately equal amounts of radicals and excited states are generated. Hence, generally it is better to study solute excited states with pulse radiolysis in non-polar solvents and solute radicals or radical ions in polar solvents. This is often not possible due to insolubility in the preferred solvent, but if the transients are being monitored via transient absorption spectroscopy and they have high molar absorption coefiicients then low yields need not be problematic. 

This reaction has been the matter of numerous studies and modifications. It seems to be most sensitive when X is an amine such as cyclohexylamine. The tetrahedral complex is intensively colored since the value of its molar absorptivity coefficient s is high (100-1000). Probably, in the formation reaction of these complexes, amine plays the part not only of a ligand but also of a base, which favors the deprotonation of the barbituric. Therefore, this part favors the complex formation. When the reaction is carried out without an amine, but in the presence of methanol, the following octahedral complex forms ... 

Chiroptical techniques allow optical distinction between chiral molecules. In the ORD (optical rotatory dispersion) method the optical rotation is recorded as a function of the wavelength. In the CD (circular dichroism) method the difference in molar absorptivity between left and right circularly polarized light is measured as a function of the wavelength. The ORD curve of (-) humulone in methanol is displayed in Fig. 4. 

C. Morterra, G. Magnacca, V. Bolis, On the critical use of molar absorption coefficients for adsorbed species the methanol/siUca system. Catal. Today 70(1-3), 43-58 (2001). doi 10. 1016/S0920-5861(01)00406-0... 

Considering that calixarenes have rather low molar absorption coefficients, more efficient chromophores were attached to calixarene moieties in order to obtain strongly absorbing ligands for and Tb + complexation. Complexes of ligand 54 containing four pyridine-TV -oxide units as chromophores showed metal luminescence upon ligand excitation in methanol (Pappalardo et al. 1991), The luminescence was completely... 

Like acridine, phenanthridine and dimethyl acetylenedicarboxylate in methanol give a high yield of 1 1 1 molar adduct. Ultraviolet absorption spectrum comparisons show that this is best formulated as 9,10-dihydro-9-methoxy-10- (tran.s-l,2-dimethoxycarbonylvinyl) phenanthridine (142) rather than the corresponding phenanthridinium methoxide (143) under neutral conditions acidification changes the spectrum to that characteristic of the phenanthridinium cation. Crystallization of the adduct (142) from methanol containing 5-15% of water gave the betaine [(144) the positions of the ester and carboxylate groups have not been established], while in the presence... 

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