Molar absorptivity values

LOD is defined as the lowest concentration of an analyte that produces a signal above the background signal. LOQ is defined as the minimum amount of analyte that can be reported through quantitation. For these evaluations, a 3 x signal-to-noise ratio (S/N) value was employed for the LOD and a 10 x S/N was used to evaluate LOQ. The %RSD for the LOD had to be less than 20% and for LOQ had to be less than 10%. Table 6.2 lists the parameters for the LOD and LOQ for methyl paraben and rhodamine 110 chloride under the conditions employed. It is important to note that the LOD and LOQ values were dependent upon the physicochemical properties of the analytes (molar absorptivity, quantum yield, etc.), methods employed (wavelengths employed for detection, mobile phases, etc.), and instrumental parameters. For example, the molar absorptivity of methyl paraben at 254 nm was determined to be approximately 9000 mol/L/cm and a similar result could be expected for analytes with similar molar absorptivity values when the exact methods and instrumental parameters were used. In the case of fluorescence detection, for most applications in which the analytes of interest have been tagged with tetramethylrhodamine (TAMRA), the LOD is usually about 1 nM. 

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 molar extinction coefficient e, associated with a wavelength of maximum absorbance Amax, is particularly useful for determining drug concentrations. For example, the concentration of tetracycline is measured at 380 nm where the molar absorptivity value is 16,200. 

TABLE 8-9. Molar Absorptivity Values for Neutral, Acid, aud Basic Species"... 

Table 6 Molar absorptivity values for nitrobenzene measured at 252 nm...

The X max. at 239 nm is typical of styrene chromophores which have undergone a wavelength shift and loss of intensity due to lack of coplanarity among the components of the chromophore. The solvent used was 95% alcohol, and a molar absorptivity value of 12,300 was obtained. The instrument used was a Cary 14-Spec trophotome ter. 

CD-ROM Tutorial Calculating Molar Absorptivity Values Using UV-VIS Spectral Data. 

Thio-Michler s ketone (formula 46.2) reduces Au(III) and forms various complexes with Au(I) (pH 1- ), generally with participation of halide ions or solvent molecules. These complexes allow the sensitive determination of Au in water-ethanol, water-DMF, CHCI3, or CHCl3-butanol media. Molar absorptivity values vary, according to the medium, from 1-10 to 2-10 at 525-560 nm [58,59]. 

The chemist in the automobile industry may be called upon not only for the manufacture of these compounds but also for the analysis in order to maintain the proper concentration of the compound. The detection in an HPLC system is most widely accomplished by UV-visible detectors. Most compounds used in production chemicals have chromophores that are detectable in the UV region. Table 2.6 shows molar absorption values for common functional groups [5], Care must be taken that the solvent used in the analysis is invisible to the analysis. As can be seen from Table 2.6, typical detection range is 180-210 nm. A chromophore is the region between two different molecular orbitals and will absorb UV light due to the conjugated system of electrons or to a metal complex bound to a transition metal to a ligand. 

The molar absorptivity values (e) of both substances may be obtained from pure standards. Once these values are known, the absorbance values for each sample obtained at both analytical wavelengths allow computing the concentration values from the following equations ... 

With the aid of the molar absorptivity value of 31600 at pH 10, as given by Fry (13), we have determined the feruloylester content of the four pectins. These are quite different (Table I). Acid-soluble and alkali-soluble pectins contain many more feruloylester groups on average one such group per pectin molecule. It is tempting to presume a relationship between feruloylester content and ease of extraction of the pectins, but this requires further study. 

Progressive substitution within the [M060(i9. ()(NAr)j2- series induces a slight but steady redshift in their electronic spectra Xmax values, accompanied by a nearly additive increase in the molar absorptivity values for these bands. The successive incorporation of [NAr] ligands into the [M06O19P framework likewise induces a steady decrease in the species 1/2 values by ca. -220 mV per [NAr] group. 

Electron transfer from donor to the acceptor moiety occurred with the formation of intensely coloured radical ions with high molar absorptivity value. The formation of charge-transfer complex of some cephem analogs (D) with iodine in 1,2-dichloroethane Q) is observed with the change of colour from violet to lemon yellow ... 

The evaluation and checking of the objectivity of the results are to a certain extent facilitated by the fact that whereas the molar absorptivity values are dependent on the wavelength, the equilibrium constants naturally are not. Hence, comparison of the equilibrium constants calculated from the concentration dependence of the absorbances measured at the different wavelengths is of assistance in the calculation of the correct constants and correct molar absorptivities. When the real equilibrium data are known, the distribution curves describing the system can be calculated and from these one can read off directly how the concentrations of the various species in solution vary with the change of the analytical concentrations (cf., Figs 8.1 and 8.2). 

Typical cross-sections and molar absorptivity values are as follows ... 

Table 7.3 Molar absorptivity values for a possible absorbance standard...

Prior to the discussion of the spectroscopic characteristics of tetrahydrofuran (THF), it should be noted that THF and many other ether compounds are chemically unstable. Over time, THF breaks down to form peroxides. Peroxides are chemically reactive and unstable. In order to help control peroxide levels in a solvent such as THF, manufacturers typically add a chemical scavenger, called a preservative or stabilizer such as 2,6-di-r-butyl-4-mefhylphenol (2,6-di-r-butyl-p-cresol, BHT). This type of THF is referred to as preserved or nonspectral grade THF. BHT has large molar absorptivity values in the UV below 280nm with the peak maximum at about 270 nm. As a consequence, preserved THF is rarely used in conjunction with UV detectors (see Fig. 1.4). 

Comparing the absorption spectra of lanthanide and actinide ions having the same number of f electrons, the most striking differences occur in molar absorptivity at the light end of the actinide series. For example, in fig. 3, approximately 100-fold larger molar-absorptivity values are evident for bands whose widths are comparable to those of Nd. Actinide-ion band molar absorptivities generally decrease across the... 

Molar absorptivity values are generally determined by phosphate analysis or from the monomer concentration. The latter is determined upon hydrolysis of the poljnner or oligomer from absorbance readings using literature E values for the monomer. The method of determination of E values may be indicated in the Note column by appropriate s5nnbols listed under Abbreviations. 

Phenols absorb at ca 280 nm [106, 107]. In the case of A02, molar absorptivity values ca 15001 mol cm per aromatic ring were proposed... 

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