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Absorbance spectrophotometry

The fine structure of the absorption band associated with the n-7T electronic transitions in A -3-ketosteroids is better resolved using chiroptical detection methods compared to absorbance spectrophotometry. Selectivity in the determination of these steroids, therefore, is increased using the solvent-dependent CD spectra of the compounds being investigated, and enhanced even more if difference CD procedures are developed [24],... [Pg.300]

More definitive compound verification may be achieved by (.1) Additional HPLC analyses under altered chromatographic conditions with an accompanying comparison of retention times of standards and unknowns or (2) Collection of component HPLC peaks and subsequent analysis by, for example, mass spectrometry, fluorescence spectroscopy, or optical absorbance spectrophotometry. [Pg.99]

The measurement of SFC by pNMR is commonly used to monitor fat crystallization. It is, however, generally less sensitive than absorbance spectrophotometry (see below) in the early stages of crystallization, as crystals can be visible before solid fat is detectable by pNMR (Wright et al., 2001a). Notwithstanding this, Wright et al. (2000) found a strong correlation between the induction time measured by pNMR and that measured by absorbance spectrophotometry for three milk fat systems. The principles of NMR are described in Chapter 20. [Pg.731]

The emphases of this section reflect the author s own special interests in using CD detection to directly determine chiral substrates. The majority of the systems described are drug substances. Direct analytical applications over the last 20 or so years have clearly demonstrated that a priori expectations of serious interference problems are ill-founded. Analytical sensitivities similar to those for absorbance spectrophotometry are readily accessible, and a high degree of analytical selectivity is obtained because of that very same property that makes ORD and CD such useful structural tools, namely, the sensitivity of a chromophore to its chiral environment. Substrates are organized into three groups ... [Pg.454]

Fluorometry is widely used for automated immunoassay. It is approximately 1000 times more sensitive than comparable absorbance spectrophotometry, but background interference caused by fluorescence of native serum can create a major problem. This interference is minimized by careful design of the filters used for spectral isolation, by the selection of a fluorophore with an emission spectrum distinct from those of interfering compounds, or by using time- or phase-resolved fluorometry (see Chapter 3). [Pg.278]

Complex leaching from the clay surface was investigated by means of atomic absorbance spectrophotometry of ruthenium on the reaction mixture and found to be below the technique s detection limit of 0.16 ppm ruthenium, indicating that less than 0.2 % of the complex is leaching. [Pg.498]

Of the optical techniques that have become part of the analyst s armory, chemiluminescence is, perhaps, the latest to have come of age. Historically, absorbance spectrophotometry with chromogenic labels has offered the clinical analyst convenience and universality, since UV/visible spectrophotometers are both ubiquitous and amenable to automation. However, direct detection of chromophores without enzyme amplification is limited in sensitivity to 0.1-1.0 jiM, since few molar extinction coefficients are greater than 10. Radiolabel techniques do offer far superior sensitivity, but as the demands for highly sensitive analyses become more voluminous and more widespread in terms of their setting (i.e., both health-... [Pg.89]

Dissolve retinoic acid m diethyl ether, and cool on ice. To this solution, add a slight excess (>1 1 molar ratio) of cold ethereal solution of diazomethane. Allow the solution to warm to room temperature, and evaporate the solvent under an inert gas or in a rotary evaporator. Dissolve the residue of methyl retinoate in an appro-pnate solvent. Confirm the formation of methyl retinoate by TLC (methyl retinoate migrates more rapidly than does retinoic acid) add more diazomethane if not all of the retinoic acid has reacted. Check the purity of the methyl ester by HPLC or TLC confirm purity and detemune concentration by absorbance spectrophotometry. [Pg.24]

Since the complexes of Fe(III) with sulphosalicyclic acid are strongly absorbing, spectrophotometry can be used in conjunction with Job s method to determine the molar ratio of Fe(lII) the acid. Iron(Ill) in chloride solution together with Co(II), can be separated in an ion exchange column. Iron(III) eluted can be monitored amperometrically using a rotating Pt electrode (J. Chem. Educ.Sl( 1974)491). [Pg.316]

Relative uncertainties for absorption spectrophotometry as a function of absorbance for the three categories of indeterminate instrumental errors (see Table 10.8 for equations). [Pg.411]

Selectivity Selectivity is rarely a problem in molecular absorption spectrophotometry. In many cases it is possible to find a wavelength at which only the analyte absorbs or to use chemical reactions in a manner such that the analyte is the only species that absorbs at the chosen wavelength. When two or more species contribute to the measured absorbance, a multicomponent analysis is still possible, as shown in Example 10.6. [Pg.412]

Selectivity The selectivity of molecular fluorescence and phosphorescence is superior to that of absorption spectrophotometry for two reasons first, not every compound that absorbs radiation is fluorescent or phosphorescent, and, second, selectivity between an analyte and an interferant is possible if there is a difference in either their excitation or emission spectra. In molecular luminescence the total emission intensity is a linear sum of that from each fluorescent or phosphorescent species. The analysis of a sample containing n components, therefore, can be accomplished by measuring the total emission intensity at n wavelengths. [Pg.433]

Theoretical Models of the Response Surface Mathematical models for response surfaces are divided into two categories those based on theory and those that are empirical. Theoretical models are derived from known chemical and physical relationships between the response and the factors. In spectrophotometry, for example, Beer s law is a theoretical model relating a substance s absorbance. A, to its concentration, Ca... [Pg.675]

In spectrophotometry the absorbance per unit length of path through the sample e is defined as... [Pg.661]

Concurrent with requirements for low levels of mercurials in discharge water is the problem of their deterrnination. The older methods of wet chemistry are inadequate, and total rehance is placed on instmmental methods. The most popular is atomic absorption spectrophotometry, which rehes on the absorption of light by mercury vapor (4). Solutions of mercury compounds not stabilized with an excess of acid tend to hydrolyze to form yeUow-to-orange basic hydrates. These frequendy absorb onto the walls of containers and may interfere with analytical results when low levels (ppm) of mercury are determined. [Pg.112]

Generally, cmde sulfur contains small percentages of carbonaceous matter. The amount of this impurity is usually determined by combustion, which requires an exacting technique. The carbonaceous matter is oxidized to carbon dioxide and water the carbon dioxide is subsequently absorbed (18). Automated, on-stream determination of impurities in molten sulfur has been accompHshed by infrared spectrophotometry (35). [Pg.124]

Minor levels of titanium are conveniently measured by spectrophotometry, eg, by the 410-nm absorbance of the yellow-orange peroxide complex that develops when hydrogen peroxide is added to acidic solutions of titanium. [Pg.134]

Hypochlorous acid can be distinguished from other chlorine species by amperometry using a membrane electrode (135). Spectrophotometry can also be used to measure HOCl via its absorbance maximum at 235 nm. Gaseous mixtures of CI2, CI2O, HOCl can be analyzed by mass spectrometry. [Pg.468]

Spectrophotometry, a simple and rehable technique, is often used in rate assays. This method can be used when the substrate or the product of the reaction absorbs in the uv or the visible region. In other cases, a nonabsorbing system can be coupled to a system in which the substrate or product absorbs in the uv or visible region. [Pg.288]

Optical methods of analysis are dependent either upon (i) measurement of the amount of radiant energy of a particular wavelength absorbed by the sample, or (ii) the emission of radiant energy and measurement of the amount of energy of a particular wavelength emitted. Absorption methods are usually classified according to the wavelength involved as (a) visible spectrophotometry (colorimetry), (b) ultraviolet spectrophotometry, and (e) infrared spectrophotometry. [Pg.7]

All infrared spectrophotometers are provided with chart recorders which will present the complete infrared spectrum on a single continuous sheet, usually with wavelength and wavenumber scales shown for the abscissa and with absorbance and percentage transmittance as the ordinates. More advanced instruments also possess visual display units on which the spectra can be displayed as they are recorded and on which they can be compared with earlier spectra previously obtained or with spectra drawn from an extensive library held in a computer memory. These modern developments have all led to quantitative infrared spectrophotometry being a much more viable and useful analytical procedure than it was just a few years ago. [Pg.747]

Oxidation of isopropyl alcohol by chromic acid in concentrated acetic acid solution has recently been studied by Wiberg and Schafer S spectrophotometri-cally. At 385 nm a rapid increase in absorbance (with a half life of about 6 sec) due to mono- and diester formation was noted. When the reaction was examined at 510 nm, first a rapid increase, then a decrease of the absorbance was found. Since at this wavelength only chromium species can absorb, the intermediate could be chromium(V) or (IV). The esr spectra of reaction mixtures showed a relatively sharp signal with a. g = 1.9805 value corresponding to chromium(V). The fact that the relative concentrations of the intermediate determined from the spectral data agree well with the intensity of esr signals, indicates that the same species is responsible for the both phenomena. It is then clear that the oxidation of isopropyl alcohol proceeds via chromium(V). [Pg.526]

The overall anthocyanin analysis is generally conducted using the Giusti and Wrolstad method based on the differences in absorbance of anthocyanins at pH 1 and pH 4.5. Then the pigment content is determined using the coefficient of molar extinction of the predominant anthocyanin. It should be noted that this technique only allows dosing of anthocyanins with a color difference between the two pH values (due to transition to the flavylium cation form). A more global analysis of total anthocyanin content may be conducted by direct spectrophotometry of the... [Pg.74]

Several collaborating laboratories (usually five participating laboratories) test the proposed substance using a variety of techniques. The relative reactivity or relative absorbance of the impurities present in a substance must be checked when a nonspecific assay method is employed, e.g. by colorimetry or ultraviolet spectrophotometry. It is particularly important to quantify the impurities when a selective assay is employed. In such a case, it is best to examine the proposed substance by as many methods as practicable, including, where possible, absolute methods. For acidic and basic substances, titration with alkali or acid is simple but other reactions which are known to be stoichiometric may be used. Phase solubility analysis and differential scanning calorimetry may also be employed in certain cases. [Pg.183]

UV/VIS spectrophotometry can be used to determine many physico-chemical characteristics of compounds and thus can provide information as to the identity of a particular compound. Although UV/VIS spectra do not enable absolute identification of an unknown, they are frequently used to confirm the identity of a substance through comparison of the measured spectrum with a reference spectrum. However, UV spectrophotometry is not highly specific, and can obviously only be applied to polymer additives which are absorbers of UV radiation, i.e. contain chromophoric groups. Both UV and IR monitor functional entities rather than the entire molecular structure. A functional group s proximity to other electropositive or electronegative structures in a molecule affects the absorbance spectrum, allowing one to infer some details of molecular structure. [Pg.304]


See other pages where Absorbance spectrophotometry is mentioned: [Pg.134]    [Pg.907]    [Pg.410]    [Pg.245]    [Pg.249]    [Pg.166]    [Pg.200]    [Pg.1343]    [Pg.192]    [Pg.134]    [Pg.907]    [Pg.410]    [Pg.245]    [Pg.249]    [Pg.166]    [Pg.200]    [Pg.1343]    [Pg.192]    [Pg.219]    [Pg.125]    [Pg.142]    [Pg.429]    [Pg.378]    [Pg.176]    [Pg.744]    [Pg.753]    [Pg.907]    [Pg.907]    [Pg.44]    [Pg.224]    [Pg.302]    [Pg.303]    [Pg.305]    [Pg.305]   
See also in sourсe #XX -- [ Pg.731 ]




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