Ultraviolet spectroscopy modification

Ultraviolet spectroscopy is used in many clinical laboratories due to its ease of operation and availability. A classical method for theophylline determination in plasma is the one of Schack and Waxier.45 The original method had interferences from phenobarbitol and various xanthine derivatives such as theobromine.46 The modification of the method by Jatlow47 eliminated the interferences from barbituates but included the various... 

Infrared and ultraviolet spectroscopies, introduced in the chemistry of natural products about three decades later, provided the first evidence to support this idea [8, 9]. The discovery of similar modification of reactivity of amino and keto groups across a nine-membered ring of vomicine [10], a strychnine congener [11], pointed to the generality of such transannular interactions in medium-size rings. This then became the topic of systematic and extensive investigations by Leonard and coworkers [12]. 

The most important methods used in in-situ studies of electrode surfaces are various modifications of reflection spectroscopy in the ultraviolet through infrared regions. For electrochemical applications, the specular reflection (at smooth electrode surfaces) is much more important than the diffuse reflection from matt surfaces. The reflectivity, R, of the electrode/ electrolyte interface is defined by ... 

Finally, and apart from the importance of micelles in the solubilization of chemical species, mention should also be made of their intervention in the displacement of equilibria and in the modification of kinetics of reactions, as well as in the alteration of physicochemical parameters of certain ions and molecules that affect electrochemical measurements, processes of visible-ultraviolet radiation, fluorescence and phosphorescence emission, flame emission, and plasma spectroscopy, or in processes of extraction, thin-layer chromatography, or high-performance liquid chromatography [2-4, 29-33],... 

There are numerous ways to determine experimentally pK values of chemical compounds (205). Classical methods are potentiometric titration and ultraviolet (UV) spectroscopy, among others. These techniques have been widely applied for nucleobases and also for metal-nucleobase complexes. For the extremes such as negative pK values (pK < —2) of singly or multiply protonated nucleobases, or very high pK values (pK >15) for deprotonation of exocyclic amino groups of nucleobases (C, G, A), modifications have to be employed. These include the consideration of the Hammett acidity function in superacidic solvents or solvent mixtures (206), as well as extrapolative techniques according to Bunnett-Olsen and Marziano-Cimino-Passerini to be applied in polar, aprotic solvents (45, 207). 

Absorption spectroscopy based on ultraviolet and visible radiation is one of the must useful tools available to the scientist for quantitative analysis. Important characteristics of spectrophotomctric and photometric methtxls include (1) wide applicability to both organic and inorganic systems. (2) typical detection limits of 10 to 10 M (in some cases, certain modifications can lead to lower limits of detection), (. ) moderate to high selectivity. (4) good accuracy (typically, relative uncertainties arc I % to. V /o. although with special precautions, errors can be reduced to a few tenths of a percent), and (5) case and convenience of data acquisition. 

Tables 1.6 and 1.7 show results obtained for styrene monomer determinations carried out on samples of polystyrene by the direct ultraviolet method and by the distillation modification of diis method. It is seen that the distillation method gives results that are consistently higher than those obtained by direct spectroscopy.

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