Additives, determination ultraviolet spectroscopy

Previous authors have taught the principles of solving organic structures from spectra by using a combination of methods NMR, infrared spectroscopy (IR), ultraviolet spectroscopy (UV) and mass spectrometry (MS). However, the information available from UV and MS is limited in its predictive capability, and IR is useful mainly for determining the presence of functional groups, many of which are also visible in carbon-13 NMR spectra. Additional information such as elemental analysis values or molecular weights is also often presented. 

Some plasticizer mixes require pretreatment, such as saponification, but in most instances chromatographic separations can be accomplished with the mix. In addition to the usual identification of substances by organochemical analysis, other methods now being used include color tests, physical tests (determinations of boiling point and refractive index), and infrared and ultraviolet spectroscopy. 

Ultraviolet spectroscopy has great utility in the characterization of expls and related materials, and serves as a primary analytical tool for the quantitative determination of reactant composition and purity. Additionally, it can provide the principal method of monitoring expl kinetics and reaction mechanisms, since the high temps characteristic of expins are effective in creating electronic excitations... 

Partition Coefficient. Partition coefficients of the TFMS herbicides in both the presence and absence of surfactant were determined between 1-octanol and pH 1.0 water (made acid by addition of HC104) by ultraviolet spectroscopy. The absorption spectrum of Tween 80 did not interfere with the spectra of the sulfonanilides (6). 

Elvidge, Proctor, and Baines72 found that oxycellulose used as a carboxylic cation-exchange column would separate phenol and chlorocresol from various alkaloids, including meperidine before determination by ultraviolet spectroscopy. IN H2S04 followed by water was used to elute the phenol and chlorocresol and additional H2S04 eluted the meperidine. This method was devised for the assay of injection formulations. 

Generally, methods are based on solvent extraction of the additive followed by analysis for the extracted additive by a suitable physical technique such as visible spectrophotometry of the coupled antioxidant, redox spectrophotometric methods, ultraviolet spectroscopy, infrared spectroscopy, gas chromatography, thin-layer chromatography or column chromatography. In general, direct chemical methods of analysis have not foimd favour. These include potentiometric titration with standard sodium isopropoxide in pyridine medium or reaction of the antioxidant with excess standard potassium bromide-potassium bromate (ie. free bromine) and estimation of the unused bromine by addition of potassium iodide and determination of the iodine produced by titration with sodium thiosulphate to the starch end-point. ... 

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. 

METHOD 98 - DETERMINATION OF MIXTURES OF ADDITIVES IN POLYMERS. THIN-LAYER CHROMATOGRAPHY - INFRARED AND ULTRAVIOLET SPECTROSCOPY. 

Determination of mixtures of additives in polymers. Thin-layer chromatography-infrared/ultraviolet spectroscopy... 

The determination of Uvitex OB illustrates an example of the application of ultraviolet spectroscopy to the determination of additives in foodstuff simulent extraction liquids. 

In many instances, visible fluorescence methods are less subject to interference by other polymer additives present in the extractant than are ultraviolet methods. Thus, Uvitex OB has an intense ultraviolet absorption at a wavelength high enough (378 nm) to be outside the region where many interfering substances in the extractant would be excited to fluoresce. Therefore, in some instances visible fluorimetry offers a method of determining an extractant constituent without interference from other constituents when this would not be possible by ultraviolet spectroscopy. 

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. 

Over the past 10 years a multitude of new techniques has been developed to permit characterization of catalyst surfaces on the atomic scale. Low-energy electron diffraction (LEED) can determine the atomic surface structure of the topmost layer of the clean catalyst or of the adsorbed intermediate (7). Auger electron spectroscopy (2) (AES) and other electron spectroscopy techniques (X-ray photoelectron, ultraviolet photoelectron, electron loss spectroscopies, etc.) can be used to determine the chemical composition of the surface with the sensitivity of 1% of a monolayer (approximately 1013 atoms/cm2). In addition to qualitative and quantitative chemical analysis of the surface layer, electron spectroscopy can also be utilized to determine the valency of surface atoms and the nature of the surface chemical bond. These are static techniques, but by using a suitable apparatus, which will be described later, one can monitor the atomic structure and composition during catalytic reactions at low pressures (< 10-4 Torr). As a result, we can determine reaction rates and product distributions in catalytic surface reactions as a function of surface structure and surface chemical composition. These relations permit the exploration of the mechanistic details of catalysis on the molecular level to optimize catalyst preparation and to build new catalyst systems by employing the knowledge gained. 

Molecular spectroscopy based on ultraviolet, visible, and infrared radiation is widely used for the identification and detennination of many inorganic, organic, and biochemical species. Molecular ultraviolet/visible absorption spectroscopy is used primcirily for quantitative analysis and is probably more extensively applied in chemical and clinical laboratories throughout the world than any other single method. Infrared absorption spectroscopy is a poweiful too for determining the structure of both inorganic and organic compounds. In addition, it now plays an important role in quantitative analysis, particularly in the area of environmental pollution. 

For photoelectron spectroscopy organic layers (neat films and mixtures) with a nominal thickness of 25 nm were deposited on 100 nm thick gold films which were thermally evaporated onto oxidised Si wafers. The electronic properties of the films were characterised using X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) by employing monochromated A1 Ka radiation (hv = 1486.7 eV) for measurement of the core levels as well as ultraviolet radiation [He I (hv = 21.2 eV) and He II (hv = 40.8 eV)] for an analysis of the occupied states near the Fermi level. For a measurement of the secondary electron cut-off to determine the sample work function exactly, an additional bias (-2 V and -5 V) was applied to the sample. 

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