Color substances

The so-called peak power delivered by a pulsed laser is often far greater than that for a continuous one. Whereas many substances absorb radiation in the ultraviolet and infrared regions of the electromagnetic spectrum, relatively few substances are colored. Therefore, a laser that emits only visible light will not be as generally useful as one that emits in the ultraviolet or infrared ends of the spectrum. Further, witli a visible-band laser, colored substances absorb more or less energy depending on the color. Thus two identical polymer samples, one dyed red and one blue, would desorb and ionize with very different efficiencies. 

LC can be used for both volatile and nonvolatile substances, but GC can handle only volatile substances. Chromatography was originally a method for separating and displaying mixtures of colored substances on a colorless column of solid material. The word chromatography is derived from chroma (color) and graph (writing). 

Zinc phosphate, Zn2(P0 2> forms the basis of a group of dental cements. Chromium and zinc phosphates are utilized in some metal-treating appHcations to provide corrosion protection and improved paint adhesion. Cobalt(II) phosphate octahydrate [10294-50-5] Co2(P0 2 8H20, is a lavender-colored substance used as a pigment in certain paints and ceramics. Copper phosphates exhibit bioactivity and are used as insecticides and fungicides. Zinc, lead, and silver phosphates are utilized in the production of specialty glasses. The phosphate salts of heavy metals such as Pb, Cr, and Cu, are extremely water insoluble. 

Dyes, on the other hand, ate colored substances which ate soluble or go into solution during the appHcation process and impart color by selective absorption of light. In contrast to dyes, whose coloristic properties ate almost exclusively defined by their chemical stmcture, the properties of pigments also depend on the physical characteristics of its particles. 

Logwood extract—A reddish brown-to-black soHd material extracted from the heartwood of the leguminous tree Haemato>y/on campechianum. The active colorant substance is principally hematein. The latent coloring material is the unoxidized or leuco form of hematein called hematoxylin. The leuco form is oxidized by air. 

Colored substance zones were obtained which could be analyzed quantitatively. The (visual) detection limits were hypericin 1 ng, rutin and chlorogenic acid 5 ng, hyperoside — quercetin 10 ng per mm chromatogram zone. The detection limits for densitometric analysis are between 20 and 50% of those for visual detection. 

Chloro-l-methyl-4-nitroimidazole (204) was also used as a heterocyclic component in the Turpin reaction. Intermediate 205 was formed under mild conditions and its cyclization was achieved by heating with ethanolic dimethylamine in a sealed tube to give a blue-colored substance, which was attributed structure 206 (Scheme 32) (52JCS784). 

By the same method one can obtain the dimaleate. Yield, 83% melting point, 146t to 148°C (crystallized by ethanol). Microcrystalline pale cream colored substance. 

Niobium pentaoxide, Nb205, also has a tendency to release oxygen into the gaseous phase upon heating [28], forming a colored substance that results from defects in the oxygen sub-lattice. 

Colored substances contain molecules with chromophores, areas of the molecule that have double bonds between carbon atoms or oxygen atoms. A good example is beta-carotene, and that section goes into more detail on how molecules become colored. Bleaches attack these chromophores in one of two ways. 

Color reactions are more or less clearly defined reactions of the substances with suitable reagents. Substance-specific reactions are not usually available, e. g. many compounds with aromatic skeletons give both a positive Vitali-Morin reaction [1 -4] and a positive Marquis reaction [4]. Again, numerous aldehydes react with electron-rich compounds in acidic medium to yield colored substances (cf. Chapters 2 and 3.1). 

The knowledge that allows chemists to describe, interpret, and predict the behavior of chemical substances is gained by making careful experimental measurements. The properties of a sample can be divided into physical properties, which can be measured without observing a chemical reaction, and chemical properties, which are displayed only during a chemical transformation. Physical properties include familiar attributes such as size, color, and mass. Some chemical properties also are familiar to us. As examples, bleach reacts chemically with many colored substances to destroy their colors, and molecular oxygen reacts chemically with many fuels to generate heat. 

The absorption of visible light of a particular frequency by atoms or molecules of a solute is perceived by our eyes as the color of this substance. Hence, only colored substances—natural or synthetic dyes— are excited by visible light. Under ultraviolet light, substances not absorbing in the visible part of the spectrum can also be... 

For preparative chromatography, the main goal is the recovery of pure mixture components. Therefore, the localization of separated bands is an important issue. The localization of bands directly on plates in daylight (for colored substances) or mostly in UV light is more convenient. The majority of adsorbents and commercially available precoated plates have a flnorescent indicator, e.g., silica gel 60 F254 -t 366. In several cases, separated bands may be localized in iodine vapors if snbstances form only unstable complexes. Brown or yellow zones produced in this way shonld be immediately outlined. 

While the classical leuco dyes 1 or 3 form colors by hydride abstraction or oxidation, the leuco dyes 4 or 5 give colored substances on contact with an acid. 

The triazole derivative, in turn, produces an intensely colored substance, III, with a diazonium compound under the experimental conditions devised for this analysis. The reactions leading to the formation of the colored substance have not yet been fully elucidated, but it appears that opening of the triazole ring as well as coupling is involved. The chemistry of the color formation will be discussed in another publication. 

The blue color is attributed to the solvated electron. The blue solutions react with ketones to form highly colored substances resembling the metal ketyls formed by reaction with the alkali metals. The blue solutions decompose into trialkylamine and hydrocarbon on standing at the boiling point of liquid ammonia. 

The simplest quantitative method for determining pH is with the use of indicators. An indicator is a colored substance usually derived from plant material that can exist in either an acid or base form. The two forms have different colors. If one knows the pH at which the indicator turns from one form to the other, one can then determine from the observed color whether the solution has a pH higher or lower than this value. Methyl orange changes color over the pH interval from 3.1 to 4.4. Below pH 3.1 it is in the acid form, which is red. In the interval from 3.1 to 4.4 it is gradually converted to the basic form, which is yellow. By pH 4.4 the conversion is complete. 

In addition to removing colored impurities and other colloids, ion exchange resins effectively remove the uncolored precursor of these colored substances. It has long been recognized that a small amount of 5-hydroxymethylfurfural (HMF), formed from dextrose by the action of acid catalysts, decomposes to form organic acids as well as pigments which polymerize to form highly colored bodies.23 Normal bone char... 

Interferences such as bubbles, undissolved particles, and color do not affect the resulting refractive index, making this method quite suitable for opaque, highly viscous, and highly colored substances such as milk and pulp liquor. 

The value of an equilibrium constant is calculated by measuring (or calculating) the equilibrium concentrations of the reactants and products. A calibration curve is constructed by measuring the absorbance of a colored solution versus its concentration. Known quantities of the reactants are mixed, and the calibration curve is used to determine the concentration of the colored substance in the resultant solution. (See the Equilibrium chapter.)... 

This experiment involves determining the amount of a substance in a solution. A calibration curve is constructed plotting the measured absorbance versus the concentration of a colored substance. The concentration of an unknown solution may be determined by reversing this process. (See the Stoichiometry chapter.)... 

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