Determination ultraviolet spectroscopic

Bonazzi et al. [18] reported the determination of miconazole and other imidazole antimycotics in creams by supercritical fluid extraction and derivative ultraviolet spectroscopic method. Cream based pharmaceuticals were mixed with celite and anhydrous sodium sulfate and extracted by supercritical fluid extractor (SFE) with... 

To correlate these changes in absorption with theory, the ultraviolet spectroscopic behavior of model compounds closely related to the degradation products isolated from bagasse native lignin, i.e., p-hydr-oxybenzaldehyde, vanillin and syringaldehyde, was determined. The compounds used were p-hydroxypropiophenone, vanillin, acetovanillone and acetosyringone and their derivatives. 

Santoni et al. have developed and used an ultraviolet spectroscopic method for the simultaneous assay of procaine and antipyrine [34]. The method allowed for a rapid and accurate determination of such mixtures over the tested concentration range of 2-9 pg/mL for procaine. 

Information about the structure of gas molecules haB been obtained by several methods. Spectroscopic studies in the infrared, visible, and ultraviolet regions have provided much information about the simplest molecules, especially diatomic molecules, and a few polyatomic molecules. Microwave spectroscopy and molecular-beam studies have yielded very accurate interatomic distances and other structural information about many molecules, including some of moderate complexity. Molecular properties determined by spectroscopic methods are given in the two books by G. Herzberg, Spectra of Diatomic Molecules, 1950. and Infrared and Raman Spectra, 1945, Van Nostrand Co., New York. The information obtained about molecules by microwave spectroscopy is summarised by C. H. Townes and A. L. Schawlow in their book Microwave Spectroscopy of Gases, McGraw-Hill Book Co., New York, 1955. 

The homolytic arylation of pyridine has been studied somewhat more systematically but by no means exhaustively. Quantitative analysis of the phenylation products using various sources of phenyl radicals has been achieved by ultraviolet spectroscopic or gas chromatographic methods. The results of some recent determinations are given in Table XV. 

Again, metabolism seems to be important in rationalizing the observed differences in the in vitro and in vivo data. If one assumes that the metabolic enzymes show some degree of stereospecificity, differences in the kinetics of metabolism for the two optical isomers would result. A kinetic study with mice on the amount of certain metabolites excreted by the kidney confirms this point of view. All nitrothiazoles of the O-type have an ultraviolet (UV) maximum at 375 m/x. Therefore all metabolites which still contain this chromophore, which is characteristic for the O-type compounds, can be collectively determined UV-spectroscopically. A comparative kinetic study of the two isomers over a 24-hour period reveals different metabolic behavior. This strongly supports the hypothesis that the kinetics of metabolism is an important factor for nitrothiazole in vivo activity. Moreover one can conclude that in this case metabolism proceeds highly stereospecifically. 

Bogomolov BD, Pivovarova VA, Gorbunova OF (1986) Determination of lignin and ether-soluble substances in aqueous solutions by fluorimetry. Khim Drev (Riga) 2 54-57 Bolker HI, Somerville NG (1962) Ultraviolet spectroscopic studies of lignins in the solid state. 

The development of a unique method (12), originally described by Strong (55) in 1941, whereby it is possible to determine the mean height of the ozone layer through measurements of the pressure-sensitive infrared absorption of the ozone molecule and comparison with determinations of the total amount of ozone based upon ultraviolet spectroscopic measurements has given added impetus to routine ozone vertical distribution determinations. This method permits the evaluation of the approximate vertical distribution of the ozone solely from the use of surface observations. Preliminary results (12) indicate that there is no simple relation between the vertical distribution of ozone and the total amount present in the atmosphere at any given time. When routine measurements are established over a network of... 

The identity of pergolide mesylate can be determined by ultraviolet spectroscopic assay at 280 nm. Using a 1 cm cell, the procedure is done at a concentration of 0.026 mg/mL pergolide mesylate in a mixture of equal parts of methanol and a solution of methionine (0.01 mg/ml) in 0.01 N hydrochloric acid. 

A colour test, specific for barbituric and thiobarbituric acids in amounts greater than 0-5 pg, uses pyridyl pyridinium dichloride as the colour reagent [111]. The quantitative determination of barbituric acid in the presence of several 5,5-disubstituted derivatives, by means of ultraviolet spectroscopic determinations and titrations in chloroform-methanol mixtures, has b n described [112]. 

Hgure 7 Influence of the modulation amplitude a [8] on the shape of a second-order derivative spectrum [19]. The example was determined by means of an aqueous sample containing approx. Imgl of each benzene, toluene, p-xylene. (Reprinted with permission from Vogt F, Tacke M, Jakusch M, and Mizaikoff B (2000) An ultraviolet spectroscopic method for monitoring aromatic hydrocarbons dissolved in water. Analytica Chimica Acta 422 187-198 Elsevier cf. Erratum (2001) Analytica Chimica Acta 431 167.)... 

Finally, an important sub-field of polymer analysis in connection with HDPE geomembranes is the analysis of additives (Freitag 1989 Zweifel 2001). In most cases an extraction procedure (typically an extraction by dissolution followed by precipitation of the polymer and filtration) precedes the chemical, chromatographic, ultraviolet-spectroscopic or infrared-spectroscopic analysis. There have been also attempts to determine additives and their contents directly in the geomembranes, e.g. by pyrolysis using subsequent gas chromatographic and mass-spectrometric determination. 

In an attempt to overcome the difficulty of interference effects by other polymer additives in the ultraviolet spectroscopic determination of phenolic antioxidants, Wexler makes use of the bathochromic shift exhibited by phenols on changing from a neutral or acidic medium to an alkaline one. This shift is due to the change of absorbing species... 

Methods 17 and 18, respectively, determine Cyasorb UV 531 (2-hydroxy-4-n-octoxybenzophenone) in polyolefins by direct infrared spectroscopy and thin-layer chromatography. Phenolic and organophosphorus type antioxidants do not interfere in these procedures. Method 19 describes an ultraviolet spectroscopic method for the determination of Tinuvin 326 ultraviolet absorber in polypropylene. 

Ultraviolet Spectroscopic Procedure. An alternate procedure for determining styrene monomer in polystyrene is based on ultraviolet spectroscopy. Styrene monomer has a strong absorption maximum of 292 nm. Unfortunately, this is subject to interference by aromatic additives, eg. antioxidants, which are often present in... 

A typical application of the procedure is given below, viz. the determination of down to 0.01% of Santonox R (4,4 -thiobis-3-methyl-6-tert-butyl phenol) in polyethylene. As this procedure determines Santonox R only in its reduced form it does not include any Santonox R which may be present in the oxidized form in the original polymer, for example produced by atmospheric oxidation of the additive during polymer processing at elevated temperatures. Total reduced plus oxidized Santonox R can be determined by ultraviolet spectroscopic procedures, for example, the differential procedure described later (Method 6) and oxidized Santonox can then be obtained by difference from the two methods. Alternatively, total unoxidized plus oxidized Santonox R can be determined by the direct ultraviolet spectroscopy. 

This ultraviolet spectroscopic procedure determines Tinuvin 326 ultraviolet absorber in polypropylene in amounts down to 0.02%. 

Figure 5.2 Calibration Curve. Ultraviolet spectroscopic determination of Uvitex OB at 378 nm in aqueous extraaants (British Plastics Federation). Reproduced from Author s own files)...

Table 5.1 Interference by other Polymer Additives in the Ultraviolet Spectroscopic Determination of Uvitex OB in Foodstuff Extractants ...

These methods are now obsolete in comparison with spectroscopic methods. Werbel has shown that the structures of these isomers are easily determined by NMR (125) (see also Table VI-5). Furthermore. 2-imino-4-thiazoline derivatives are characterized by their stretching C=N vibration at 1580 cm , absent in their 2-aminothiazole isomers, and by the stretching NH vibration that appears in the range of 3250 to 3310 cm for the former and between 3250 to 3340 cm" for the latter (131). Ultraviolet spectroscopy also differentiates these isomers (200). They can be separated by boiling in ethanol the thiazoline isomer is usually far less soluble in this solvent (131),... 

The presence of iminium salts can be detected by chemical means or by spectroscopic methods. The chemical means of detecting iminium salts are reactions with nucleophiles and are the subject of this review. The spectroscopic methods are more useful for rapid identification because with the large number of model compounds available now the spectroscopic methods are fast and reliable. The two methods that are used primarily are infrared and nuclear magnetic resonance spectroscopy. Some attempts have been made to determine the presence of iminium salts by ultraviolet spectroscopy, but these are not definitive as yet (14,25). 

In general, physical methods have been used to study tautomerism more successfully than chemical methods, and, of the physical methods, those involving measurements of basicities and ultraviolet spectra are the most important, followed by those involving measurement of infrared and proton resonance spectra. An attempt is made here to delineate the scope and to indicate the advantages and disadvantages of the various methods. A short review by Mason of the application of spectroscopic methods appeared in 1955. Recently a set of reviews on the applications of physical methods to heterocyclic chemistry has appeared, which treats incidentally the determination of tautomeric structure. 

Mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy are techniques of structure determination applicable to all organic molecules. In addition to these three generally useful methods, there s a fourth—ultraviolet (UV) spectroscopy—that is applicable only to conjugated systems. UV is less commonly used than the other three spectroscopic techniques because of the specialized information it gives, so we ll mention it only briefly. 

The most basic method for the determination of the methylxanthines is ultraviolet (UV) spectroscopy. In fact, many of the HPLC detectors that will be mentioned use spectroscopic methods of detection. The sample must be totally dissolved and particle-free prior to final analysis. Samples containing more than one component can necessitate the use of extensive clean-up procedures, ajudicious choice of wavelength, the use of derivative spectroscopy, or some other mathematical manipulation to arrive at a final analytical measurement. A recent book by Wilson has a chapter on the analysis of foods using UV spectroscopy and can be used as a suitable reference for those interested in learning more about this topic.1... 

Tao et al. [658] have described a procedure in which antimony and arsenic were generated as hydrides and irradiated with ultraviolet light. The broad continuous emission bands were observed in the ranges about 240-750 nm and 220 - 720 nm, and the detection limits were 0.6 ng and 9.0 ng for antimony and arsenic, respectively. Some characteristics of the photoluminescence phenomenon were made clear from spectroscopic observations. The method was successfully applied to the determination of antimony in river water and seawater. The apparatus used in this technique is illustrated in Fig. 5.16. 

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