Ultraviolet absorbance spectroscopy

Wolk, J., Spaid, M., Jensen, M., MacReynolds, R., Steveson, K., Chien, R., Ultraviolet absorbance spectroscopy in a 3-dimensional microfluidic chip. Micro Total Analysis Systems, Proceedings 5th pTAS Symposium, Monterey, CA, Oct. 21-25, 2001, 367-368. 

Another major asset in the routine purification and analysis of the eicosanoids is high-performance liquid chromatography (HPLC). In particular, reversed-phase HPLC has proven to be extremely effective, especially when combined with radioactive, spectroscopic or immunochemical detection methods.For example, the combination of reversed-phase HPLC with ultraviolet absorbance spectroscopy was instrumental to the discovery of leukotrienes and lipoxins, and it is still widely used to detect these compounds as well as other ultraviolet-absorbing eicosanoids. ... 

Ultraviolet-visible spectroscopy has played only a minor role in the investigation of the thietanes and its counterparts. As expected, the colorless compounds absorb in the UV region below 300 nm. For photolysis experiments, many phenylated and alkylated thietanes and thietane oxides have been measured in methyl cyanide or methanol by Langendries and de Schryver. The spectra exhibit a maximum in the vicinity of 250-265 nm ( 12,000-25,000). 

Wolfender, J.-L., Ndjoko, K. and Hostett mann, K., Liquid chromatography with ultraviolet absorbance-mass spectrometric detection and with nuclear magnetic resonance spectroscopy a powerful combination for the on-line structural investigation of plant metabolites, J. Chromatogr., A1000, 437-455 (2003). 

Let us use an example to illustrate how the ANOVA calculations are performed on some test data. A chemist wishes to evaluate four different extraction procedures that can be used to determine an organic compound in river water (the quantitative determination is obtained using ultraviolet [UV] absorbance spectroscopy). To achieve this goal, the analyst will prepare a test solution of the organic compound in river water and will perform each of the four different extraction procedures in replicate. In this case, there are three replicates for each extraction procedure. The quantitative data is shown below. 

Solvents used for spectroscopy, especially nmr and uv, should be of high purity. Many suppliers provide spectroscopic grade solvents which are particularly suitable for uv spectroscopy because ultraviolet absorbing impurities have been removed. 

See spectroscopy resonance (2) ultraviolet absorber excited state. 

A solvent for ultraviolet/visible spectroscopy must be transparent in the region of the spectrum where the solute absorbs and should dissolve a sufficient quantity of the sample to give a well-defined analyte spectrum. In addition, we must consider possible interactions of the solvent with the absorbing species. For example, polar solvents, such as water, alcohols, esters, and ketones, tend to obliterate vibration spectra and should thus be avoided to preserve spectral detail. Nonpolar solvents, such as cyclohexane, often provide spectra that more closely approach that of a gas (compare, for example, the three spectra in Figure 24-14). In addition, the polarity of the solvent often influences the position of absorption maxima. For qualitative analysis, it is therefore important to compare analyte spectra with spectra of known compounds measured in the same solvent. 

Whilst spectroscopy techniques can be used on their own to obtain spectral information about a sample they are also commonly incorporated as a detector as part of another technique, for example the use of an ultraviolet absorbance detector as part of a liquid chromatography system. In recent years there has been much enthusiasm for the research and development of hyphenated techniques, that is the interfacing/linking together of two or more techniques, because of the enhanced additional data that can be generated. 

Detection of these chemicals by ultraviolet absorption spectroscopy (ASTM D-2269) measures the absorbance over the wavelength range of 260-350 nm in a 10-mm cell of a dimethyl suffone extract of the oil. The polynuclear aromatic hydrocarbons present in the mineral oils are concentrated. In fact, the ultraviolet absorption level corresponds, approximately, to a maximum polynuclear aromatics content of about 5 ppm. 

J. Keck, M. Roessler, C. Schroeder, G.J. Stueber, F. Waiblinger, M. Stein, D. LeGourrierec, H.E.A. Kramer, H. Hoier, S. Henkel, P. Fischer, H. Port, T. Hirsch, G. Rytz, and P. Hayoz, Ultraviolet Absorbers of the 2-(2-hydroxyaryl)-l,3,5-triazine class and their methoxy derivatives fluorescence spectroscopy and X-ray structure analysis, J. Phys. Chem. B 1998, 102, 6975-6985. 

The action of all UV absorbers depends on the Lambert-Beer law, and the absorption properties of the UV absorber. The further the absorption edge extends into the near UV region, the more UV light can be filtered out. Of the four UV absorber classes shown above, the hydroxyphenylbenzotriazoles have the broadest absorption band [5.8], [5.12], In addition to thermal stability [5.12] and stability to extraction with water or organic solvents, photochemical stability is important [5.13]-[5.15], Ultraviolet reflection spectroscopy can be used to establish whether the employed UV absorber is still effective, even after several years external weathering [5.16]. 

The disappearance of the photoinitiator upon UV exposure was followed by real time ultraviolet (RTUV) spectroscopy (Beckman DU-7400) by setting the wavelength at its maximum absorbance and monitoring continuously its decrease with exposure time. 

Water Less than 0.50% by Infrared spectroscopy Ultraviolet absorbance ... 

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