Specific ultraviolet absorbance

Kitis M., Karanlil T., Kilduff J. E., and Wigton A. (2001a) The reactivity of natural organic matter to disinfection byproducts formation and its relation to specific ultraviolet absorbance. Water Sci. Technol. 43, 9-16. 

Weishaar, J.L. et al.. Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon. Environ. Sci. Technol, 37, 4702, 2003. 

Wea.ther lbillty. One of the more destmctive elements is exposure to sunlight specifically, ultraviolet (uv) light. AH sealants are affected by weathering, but there is much difference in the effect of weathering on different sealants. Most sHicones are stable with respect to uv exposure. Urethanes and polysulfides show effects of uv exposure, but can be formulated with uv absorbers to provide reasonable lifetimes in most appHcations. However, there are exceptions in aH classes of sealants and specifiers must be carehil to look for test data that has proven a specific sealant s durabHity. The source of the test data is also important data from an independent testing laboratory is generaHy apt to be more reHable. 

Infrared spectra and the degree of specific rotation show typical features of the malic acid polyester (Table 3). Ultraviolet absorbance spectra of )3-poly(L-malate) from both P. polycephalum and Aureobasidium sp, A-91 are similar and are reminiscent of malate itself [4,5]. For a solution of 1.0 mg/ml polymer, absorbance increases from 0.40 units at 230 nm to 10 units at 190 nm wavelength. After saponification and pH-neutralization, the absorbance increased from 8.7 units at 230 nm to 100 units at 190 nm. 

Paints are complex formulations of polymeric binders with additives including anti-corrosion pigments, colors, plasticizers, ultraviolet absorbers, flame-retardant chemicals, etc. Almost all binders are organic materials such as resins based on epoxy, polyurethanes, alkyds, esters, chlorinated rubber and acrylics. The common inorganic binder is the silicate used in inorganic zinc silicate primer for steel. Specific formulations are available for application to aluminum and for galvanized steel substrates. 

Removal of ultraviolet absorbing organics by passage through a specific ion exchange resin such as Amberlite XAD-2. 

The dehydrogenases discussed in this section catalyze the oxidation of alcohols to carbonyl compounds. They utilize either NAD+ or NADP+ as coenzymes. The complex of the enzyme and coenzyme is termed the holoenzyme the free enzyme is called the apotnzyme. Some dehydrogenases are specific for just one of the coenzymes a few use both. The reactions are readily reversible, so that carbonyl compounds may be reduced by NADH or NADPH. The rates of reaction in either direction are conveniently measured by the appearance or disappearance of the reduced coenzyme, since it has a characteristic ultraviolet absorbance at 340 nm. The reduced coenzymes also fluoresce when they are excited at 340 nm, which provides an even more sensitive means of assay. 

Polystyrene light stabilization has been achieved with a variety of ulfravioler absorbers including the benzophenones, benzotriazoles. and salicylates. While yellowing of polystyrene occurs in many applications, it is particularly noticeable in diffusers used with fluorescent lights. This problem has been effectively solved by using ultraviolet light absorbers. In this instance, superior stabilization is achieved when the ultraviolet absorber is used in conjunction wirh specific antioxidants. 

Because the vitamins occur in food in trace quantities, detection sensitivity is often an issue. Ultraviolet absorbance is the most common detection method. Fluorescence and electrochemical detection are used in specific cases where physicochemical properties permit and where increased sensitivity and selectivity are desired. Refractive index is seldom used, due to its lack of specificity and sensitivity. 

Exposure to toluene can be detected by extracting hippuric acid from acidified urine into diethyl ether or isopropanol and direct ultraviolet absorbance measurement of the extracted acid at 230 nm. When the analysis is designed to detect xylenes, ethylbenzene, and related compounds, several metabolites related to hippuric acid may be formed and the ultraviolet spectrometric method does not give the required specificity. However, the various acids produced from these compounds can be extracted from acidified urine into ethyl acetate, derivatized to produce volatile species, and quantified by gas chromatography. 

Ultraviolet Absorption (polynuclear hydrocarbons) A sample meets the ultraviolet absorbance specifications required by the U.S. Food and Drug Administration for Petrolatum. 

Revision Description revised Heavy Metals (as Pb) and Ultraviolet Absorbance specifications and determinations deleted Tridodecylamine specification revised Readily Carbonizable Substances test replaced Residue on Ignition test reworded. ... 

HPLC = high-performance liquid chromatography LOD = level of detection NPD =nitrogen-phosphorus detector PRA = pararosaniline RSD = relative standard deviation SPE = solid phase extraction PSD = thermionic specific detection UV = ultraviolet absorbance detection... 

The procedure tests the product as a whole, without including any separation or fractionation steps to concentrate the absorptive fractions. When wax or petrolatum is tested in this procedure, the specimen is dissolved in ixo-octane, and the ultraviolet absorbance is measured at a specihed wavelength such as 290 nm. The absorptivity is then calculated. This procedure, as such, is not a part of the federal specification. 

Ultraviolet absorbers are the most widely utilized of the photostabilizers. Most common UV absorbers are low molecular weight derivatives of o-hydroxybenzophe-none, o -hydroxybenzotriazole, or o-hydroxyphenyl salicylate [3], Most polymers are sensitive to UV radiation between 300 and 360 nm. They absorb UV radiation through their structure structural irregularities or impurities also have an effect [3], Table 4.1 shows some activation spectra for some typical polymers [3], Individual polymers absorb UV radiation within specific wave length regions, exhibiting activation spectra maxima at the wavelength where each is most vulnerable to photo-oxidation [4],... 

Certain secondary amine compounds are commonly used for chemical derivation of isocyanates which, like phosgene, form substituted urea compounds amenable to chromatographic determination. One of the most common of these reagents is 1—(2—pyridyl)-piperazine (PYP) PYP reacts on a one-to-one basis with isocyanate compounds yielding a stable urea derivative which can be quantified specifically and sensitively with reversed phase, high performance liquid chromatography (HPLC) and ultraviolet absorbance detection. 

The great and obvious limitation of the ultraviolet detectors is that they are restricted to ultraviolet absorbing compounds. Fortunately a large number of biochemically important substances absorb ultraviolet light and this detector is thus the first choice for general chromatographic work, unless the detector is chosen for a specific application. 

Detectors which monitor a specific property of the solute which is not shared with the solvent, e.g. ultraviolet absorbance and fluorescence. Possession of such a property by the solute affords its detection in the effluent. 

Initial application of ion exchange to modern LC depends on the analyte having a specific property such as ultraviolet absorbance, fluorescence or radioactivity. As many ion exchange methods require the presence of com-plexing agents (EDTA, citrate) and various electrolyte additions to achieve the required resolution, conductivity detectors could not be used without modification of the technique, since this parameter is a universal property of ionic species in solution. 

Initially, application of ion exchange to modem LC depended upon the analyte having a specific property, such as, ultraviolet absorbance. 

Hyllbrant B, Tyrefors N, Markides KE, Langstrom B. On the use of liquid chromatography with radio- and ultraviolet absorbance detection coupled to mass spectrometry for improved sensitivity and selectivity in determination of specific radioactivity of radiopharmaceuticals. J Pharm Biomed Anal 1999 20 493-501. 

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