Color absorption wavelength

All the alkali metals have characteristic flame colorations due to the ready excitation of the outermost electron, and this is the basis of their analytical determination by flame photometry or atomic absorption spectroscopy. The colours and principal emission (or absorption) wavelengths, X, are given below but it should be noted that these lines do not all refer to the same transition for example, the Na D-line doublet at 589.0, 589.6 nm arises from the 3s — 3p transition in Na atoms formed by reduction of Na+ in the flame, whereas the red line for lithium is associated with the short-lived species LiOH. 

To determine the amylose content of starch, the iodine reaction has been most commonly used because amylose and amylopectin have different abilities to bind iodine. The methods such as blue value (absorbance at 680 nm for starch-iodine complex using amylose and amylopectin standards), and potentiometric and amperometric titration have been used for more than 50 years. These procedures are based on the capacity of amylose to form helical inclusion complexes with iodine, which display a blue color characterized by a maximum absorption wavelength (kmax) above 620 nm. During the titration of starch with iodine solution, the amount (mg) of iodine bound to 100 mg of starch is determined. The value is defined as iodine-binding capacity or iodine affinity (lA). The amylose content is based on the iodine affinity of starch vs. purified linear fraction from the standard 100 mg pure linear amylose fraction has an iodine affinity of 19.5-21.0mg depending on amylose source. Amylopectin binds 0-1.2mg iodine per 100mg (Banks and Greenwood, 1975). The amylose content determined by potentiometric titration is considered an absolute amylose content if the sample is defatted before analysis. 

Neutral flavin radicals have a blue color (the wavelength of the absorption maximum, A.max, is -560 nm) but either protonation at N-l or dissociation of a proton from N-5 leads to red cation or anion radicals with imax at -477 nm. Both blue and red radicals are... 

The various photochromic parameters which were taken into account in the case of 243 were absorption wavelengths of the closed and open forms, rate constants of thermal bleaching (kA) and coloration ability or colorability (measured as the absorbance A0 immediately after the irradiation flash) (00JPO523). 

When a polyene reaches a certain length, its absorption wavelength will appear in the visible region, i.e. X is between 400 and 700 nm. When this occurs, the polyene is colored. One of the better known colored polyenes is /S-carotene, which is responsible for orange color of carrots. It has the structure ... 

The o(m, p)-PBTMS-PPV series shows very similar absorption profiles with those of PMEH-PPV polymers. The maximum absorption wavelengths of o(m)-PBTMS-PPV are blue-shifted for the same reason as that of o(ra)-PMEH-PPV. But PBTMS-PPV polymers show about 20-50 nm blue-shifted absorption maxima compared to those of PMEH-PPV series, because the trimethylsilyl substituent has little electron-donating property. The PL spectra show very drastic changes in emission color because of the substituents and kink effects. Figure 19 shows PL emission profiles of the polymers mentioned above. 

The separated spots, obtained by subjecting a paprika color standard, after saponification, to CIS TLC under the conditions described above, were then subjected to scanning densitometry. The visible absorption spectra were scanned in the wavelength range of 370-700 nm, and excellent visible absorption spectra were obtained (Fig. 3A). The spectrum of the main spot (Rf=0.50) of the paprika color, after saponification, showed its maximum absorption wavelength at 480 nm, which identically matches the spectrum of the capsanthin standard (Fig. 3C). 

Metal Complex Color Maximum Wavelength of Absorption (nm)... 

The final class of photosynthetic bacteria, the green sulfur bacteria, are named because of differences in the chemical structure of their bacte-riochlorophyll and carotenoids, giving rise to a different set of absorption bands in whole cells from their purple counterparts. This has little to do with their actual color but refers to the direction of shift of absorption wavelengths in the infrared. As photoautotrophic, strict anaerobes using sulfide or thiosulfate as an electron source, they resemble the purple sulfur bacteria and have similar electron transport chains. The sulfur that is formed as an intermediate between sulfide and sulfate is deposited out-... 

Assessing the color of white wines is much more complex, as the spectrum has no defined maximum in the visible range. Absorption is continuous from 500 to 280 mn, with a maximum in the UV range. It is difficult to use the spectrum to translate the visual impressions corresponding to dry white wines, sweet white wines and oxidized dry white wines. As the characteristic absorption wavelength of yellow substances is 420 mn, measurements of optical density at this value provide only an approximate assessment of color. 

Among the phenolic components identified, derivatives of quercetin, caffeic acid and p-coumaric acid are all more-or-less intensely yellow-colored. The maximum absorption wavelengths are between 310 and 350 nm. Tannins,... 

The simplest method for the determination of amino acids is reaction with ninhydrin. Ninhydrin reacts with both primary and secondary amino acids to produce Ruhemann s purple, which can be detected by ultraviolet (UV)-visible spectroscopy. The reaction requires heat, and a reducing agent is generally added to stabilize the color formation. Primary amines are detected with the greatest sensitivity at 570 nm, while the absorption maximum for secondary amines is 440 nm. If both primary and secondary amines are to be determined, a common absorption wavelength of 500 nm is employed however, this leads to decreased sensitivity. Under optimal... 

Iron-carbamate complex Absorption wavelength (nm) Extinction coefficient (1 mol ) Color... 

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