UV Absorption Methods

UV3346) offer superior compatibility, low volatility, excellent resistance to extraction and contribute to heat stability. The nonextractable nature of these additives makes their quantification challenging. The quantification of Chimassorb 944 in polyolefins is possible using an UV absorption method after dissolution of the polymer [596]. 

Continuous analytical methods (amperometric and UV-absorption methods) are advantageous. However, sometimes only discontinuous methods (titrimetric and some photometric methods) are available due to expense. In such cases it is important to measure immediately after sampling to avoid the decay of ozone and in the case of liquid ozone to avoid degassing. Discontinuous photometric methods requiring the addition of chemicals to the sample can be converted to a continuous method by combination with flow injection analysis (FIA). This analytical technique requires instrumentation and is not easy to handle. 

The UV-absorption method, with which quantitative determination of DNA in tissue sections can be done, provided the inspiration for the development of x-ray spectrographic methods at the end of the 1940s. The quantitative x-ray analysis methods were developed to provide quantitative elementary analysis on a histochemical and cytochemical scale, that is, quantitative elemental analysis of tissues in situ and at a subcellular level. Engstrom1 formulated how the problem could be attacked in the following way ... 

Ion-pair acidity is an important parameter to probe highly diluted solutions, as demonstrated by the sophisticated visible or near-UV absorption methods developed mainly by Streitwieser and coworkers. This analytical approach afforded the pXa values and aggregation states of a large set of cesium and lithium enolates. Its principle relies... 

Is it possible to determine substance X by UV absorption methods, or is it promising under given conditions ... 

Protein content was measured using an UV absorption method described in ref. 15. The UV method was successfully calibrated with a set of Kjeldahl protein values of GMP samples. 

A novel technique in UV detection was used by Mayer and Miller and Maclean, who measured proteins and peptides at 191-194 nm, thereby increasing the applicability of the UV absorption method. A number of workers have shown the potential of monitoring the eluent at two or more wavelengths simultaneously . This can be done by using two detectors in series, or by combining techniques in one detector. The extra information can be used for verification of tentative identification or for resolving partially merged peaks . 

Another approach to the analysis of mRNA transfer to the ribosomes is the study of cytoplasmic particles containing newly formed cytoplasmic mRNA. Leytin et al. (1971) have found that the material containing newly formed mRNA is somewhat less dense in the CsCl gradient than polysomes formed earlier. For example, while the bulk of polysomes have a buoyant density of 1.55 to 1.56 g/cm, the newly formed material possesses a density of 1.47 to 1.53 g/cm. Newly formed particles comprise only a small fraction of the total material since they cannot be detected by routine UV absorption methods. With more detailed analysis two newly formed components may be observed component A with p = 1.49 g/cm and component B with p = 1.52 g/cm. After long-term incubation, or in the presence of actinomycin D (chase experiment), almost all radioactive material is transferred from A to B peaks to the main peak of the polysomes. Inhibition of protein synthesis by cycloheximide interferes with these polysome transformations, and the label representing newly synthesized material accumulates in component A (p = 1.49 g/cm ). Thus one can suggest that component A converts to B and the latter is transformed into mature polysomes. It was found further than... 

UV absorption method. Most enzyme proteins absorb UV light at an absorption maximum at 275-280 nm due to their content of tyrosine and tryptophan. If a pure enzyme is available, the absorbance at 280 nm can be used for quantitation for many enzyme proteins, a solution containing 1 mg of protein per milliliter has an absorbance of 1.0 at 280 nm. However, others differ in their absorbance with more than an order of magnitude due to the... 

UV absorption method Enzymes exhibit UV absorption maxima 280nm, based on their content of tyrosine and tryptophan residues. To increase the detectability, measurements at 215/225 nm are used because of the peptide bond 100-1000ngmr (280nm) 5-100ngml (215/225 nm)... 

Lowry method. The Lowry method is the most generally accepted owing to its sensitivity, simplicity, and reproducibility it is 20 times more detectable than the UV absorption method and 100 times more sensitive than the biuret method. Since the color development in the Lowry method depends on the content of aromatic amino acid residues, the variation of response with different proteins is surely greater than in the biuret method but generally less than in UV adsorption measurement. 

In parallel with the differential UV absorption method mentioned previously, a differential chemical shift method had been designed and employed experimentally. For example, to find the binding site of a compound-ascomysin, a slightly modified compound-3 l-keto-32-desoxyascomysin is synthesized. Comparison between the chemical shifts of the two compounds clearly indicates that the cyclohexyl ring is the binding site ... 

Since the determination of inhibitors in polymers by Drushel et al. [13] little information has been added to the literature on the quantitative aspects of the direct examination of polymer films by phosphorescence spectroscopy. These authors examined phosphorescence (at liquid-nitrogen temperature) of thin EPR films containing Santonox R (2,2 -di-methyl-5,5 -di-r -butyl-4,4 -dihydroxydiphenyl sulfide) and V-phenyl-2-naphthyl-amine (PBN). The rather intense phosphorescence of PBN may be used to advantage when other additives interfere in the UV absorption method. As to quantitative phosphorescence analysis, several factors, e.g. film thickness, concentration quenching, and background absorption, etc., affect the linearity of the analytical working curves and precision of the measurements [13]. The reliability of a correlation between stabiliser concentration in the film and phosphorescence intensity at 77 K is also influenced by the degree of crystallinity [544]. 

The direct meastirements of the rate constants of the reaction of hydroxymethyl cyclohexadienyl radical with O2 has been made using the UV absorption method (Sect. 5.2.10), and the values of 2.5 x 10 cm molecule for benzene (Bohn and Zetzsch 1999 Grebenkin and Krasnoperov 2004 Raoult et al. 2004 Nehr et al. 2011), 6.0 x 10 cm molecule s for toluene (Knispel et al. 1990 Bohn 2001) are reported. Therefore, most hydroxymethyl cyclohexadienyl radicals are thought to react solely with O2. Also, the unimolecular decomposition rate of cyclohexadienyl radical from benzene back to CgHg + OH has been reported as (3.9 1.3) s at 298 K (Nehr et al. 2011). 

UV absorption method The superabsorbent polymer is swollen in blue dextrin aqueous solution. Water uptake is calculated by the difference from the reference solution. 

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