UV spectrometry

Ozone in the gas phase can be deterrnined by direct uv spectrometry at 254 nm via its strong absorption. The accuracy of this method depends on the molar absorptivity, which is known to 1% interference by CO, hydrocarbons, NO, or H2O vapor is not significant. The method also can be employed to measure ozone in aqueous solution, but is subject to interference from turbidity as well as dissolved inorganics and organics. To eliminate interferences, ozone sometimes is sparged into the gas phase for measurement. 

This led to the conclusion that these amino acids were essential for the resolution capability and only 6 new libraries of 18 compounds had to be synthesized with these amino acid residues to define the position 3. Surprisingly, the separation abilities of all six libraries were very similar. Therefore, tyrosine was chosen for continuing deconvolution, since it is convenient as its aromatic ring can easily be detected by UV spectrometry. The last step, defining position 5, required the synthesis and testing of 6 individual hexapeptides. 

Quantitative analysis of the peroxy group of macroinitiators is performed by iodometry [38] and that of the azo group is done by ultraviolet (UV) spectrometry. Recently, type II MAI composed of PU was determined of its azo concentration by UV [20]. When the UV absorption spectral peak of the azo group overlaps other peaks, DSC is available by determining the azo group from the exothermal peak area [1IJ. 

Cepeda, A., Paseiro, P., Simal, J., and Rodriguez, J.L., Determination of caffeine by UV spectrometry in various types of coffee green coffee and natural roasted... 

Sjoeberg, A.M. and Rajama, J., Simple method for the determination of alkaloids in cocoa using paper chromatography and UV spectrometry, J. Chromatography, 295,291,1984. 

Classical methods for the investigation of complex formation equilibria in solution (UV/Vis spectrometry, thermochemical and electrochemical techniques) are still in use (for an appraisal of these and other methods see, e.g., ref. 22). Examples for the determination of the ratio of metal to ligand in an Hg-protein complex by UV spectrometry are given in ref. 23, for the study of distributions of complex species of Cd in equilibria by combined UV spectrometry and potentio-metry in ref. 24 and by potentiometry alone in ref. 25, and for the combination of calorimetry and potentiometry to obtain thermodynamic data in ref. 26. 

Unlike methane and the other alkanes, aromatic hydrocarbons have absorptions in the UV part of the spectrum, and thus may be detected through UV spectrometry using silica fibers. This scheme is useful for "aromatic" water pollutants such as toluenes and xylenes with their absorption bands between 250 and 300 nm. Similarly, nitrate anion can be monitored (albeit with low sensitivity) in water via its UV absorption at 250 nm. 

Attempts to isolate pure C-AIR (107) were unsuccessful due to its instability in acid solution and toward heat resulting in decarboxylation giving AIR (106) (57JA1511). Using UV spectrometry, transformation of C-AIR... 

Visible and UV spectrometry are of secondary importance to other spectral methods for the identification and structural analysis of unknown compounds. This is a direct consequence of the broad bands and rather simple spectra which make differentiation between structurally related compounds difficult. As an adjunct to infrared, magnetic resonance and mass spectrometry, however, they can play a useful role. They can be particularly helpful in confirming the presence of acidic or basic groups in a molecule from the changes in band position and intensity associated with changes in pH (p. 369). 

The use of visible and UV spectrometry for quantitative analysis by comparing the absorbance of standards and samples at a selected wavelength is one of the most widespread of all analytical techniques. It is also one of the most sensitive. The analysis of mixtures of two or more components is facilitated by the additivity of absorbances. This has been discussed earlier (p. 356). Other applications include measurement of the absorption of complexes as a function of solution conditions or time to establish their composition, and to determine thermodynamic and kinetic stability for analytical purposes or for more fundamental studies. 

Lorusso et al. [109] described an HPLC method for assaying iomeprol in plasma and urine samples. Before chromatography, the biological fluids were treated with ion-exchange resins and iopamidol was added as internal standard. Detection was by UV spectrometry at 245 nm. 

Using UV spectrometry with EtdBr as a fluorescent probe of the DNA structure, the following results were obtained ... 

S Hamai, H Sakurai. 2H20 effects on the inclusional complexation of cyclodextrin with sodium 2-naphthalenesulfonate in capillary electrophoresis and UV spectrometry. J Chromatogr A 800 327-332, 1998. 

Many experimental techniques were used to examine polymerization kinetics and products of template polymerization. In kinetic measurements, many conventional methods of determination of monomer concentration were applied, very often UV spectrometry or bromometric titration. For many systems examined, bromometric titration gives results comparable with the results obtained by other methods. However, systems were found in which the method successful for blank reaction gives results incomparable with another analytical methods. Perhaps some specific reaction with the complex formed affects the analytical procedure." ... 

Determination of Enthalpy of Vaporization of Pure Liquids by UV Spectrometry 203... 

As a consequence of the advances in NMR, UV spectrometry has been further marginalized for our purposes, and the UV chapter has been dropped—a difficult decision (nostalgia perhaps) because UV spectrometry is widely used for other purposes. Students should understand the relationship between absorption of visible-UV frequencies and molecular structure. But such general understanding is presented in most first-year organic texts. We cannot justify 26 pages of text and tables to describe a technique that is outmoded for structure elucidation and, in practice, virtually abandoned except for special situations. 

Data from G. Marin-Puga, M. Guvnan L, and F. Hevia, Determination of Enthalpy ofVaporizotion of Pure Liquids by UV Spectrometry," J. Chem. Ed. 1995, 72, 91. 

Burgess. C. and D.G. Jones Spectrophotometry. Luminescence and Colour Science and Compliance Papers Presented at the Second Joint Meeting of the Uv Spectrometry Group of the u, Elsevier Science, Ltd, New York, NY, 1995. Evans, NJ. Impedance Spectroscopy Reveals Materials Characteristics, Adv. Mat.. Proc.. 41 (November 1991). 

Alkylthiocarbamate or thiocarbamate herbicides have been determined by various analytical methods, e.g., UV spectrometry, thin-layer chromatography, IR spectrometry, and gas chromatography. 

Rasierowska (1+5) has applied alternate-current oscillopolarographic method to pharmaceuticals containing saccharin and sodium saccharin. Both forms a well developed oscillopolarographic curve in MH2SOI1 in air with mercury anode and dropping-mercury cathode, and the results are comparable to those obtained by UV spectrometry. 

The solubility of silver sulfadiazine has been determined by equilibrating the compound in doubly distilled water at 25 C and the measurements of the saturated solution for sulfadiazine by UV spectrometry and for silver by atomic absorption spectroscopy (7). Nesbitt and Sandmann (22) measured the equilibrated solution for silver using a silver-ion selective electrode. Their measurements were performed at 25°C in nitric acid -potassium nitrate buffers (pH 2-3) and ionic strength 0.1. 

OP-UV spectrometry can be used to measure vapors or gases that have weak absorption characteristics, and therefore, low sensitivities in the IR spectrum. These include such compounds as nitrogen oxides, formaldehyde, ozone, sulfur dioxide, benzene, toluene, and xylenes, and also homonuclear diatomic molecules, such as chlorine. The compounds that can be determined by UV are much fewer (see Table 3.43) than those that are absorbing in the IR spectra. 

Nuclear magnetic resonance (NMR) spectrometry is basically another form of absorption spectrometry, akin to IR or UV spectrometry. Under appropriate conditions in a magnetic field, a sample can absorb electromagnetic radiation in the radio frequency (rf) region at frequencies governed by the characteristics of the sample. Absorption is a function of certain nuclei in the molecule. A plot of the frequencies of the absorption peaks versus peak intensities constitutes an NMR spectrum. This chapter covers proton magnetic resonance ( H NMR) spectrometry. 

These sites can be studied by electron paramagnetic resonance (EPR), ultraviolet (UV) spectrometry, x-ray photoelectron spectroscopy (XPS), and other methods. Besides, a quantitative study of redox sites can be carried out with the help of a volumetric or gravimetric study of the adsorption of the oxidizing or the reducing molecules. 

---