Colorants test form

The best chemiccil color tests form a natural partnership with the micnxrystal tests, in which each kind not only adds to the other but does so when most needed, making good some of the other s inevitable deficiencies.. .. Any controversy over which is better is absurd, since both should be used."... 

Salicylaldehyde gives a yellow coloration and forms salicylic acid very slowly. Cannizzaro s reaction is also given by formaldehyde but, owing to the difficulty in isolating the products, is not used as a test. 

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

Filtered-Particle Inspection. Solids containing extensive inteiconnected porosity, eg, sintered metallic or fired ceramic bodies formed of particles that ate typically of 0.15-mm (100-mesh) screen size, are not inspectable by normal Hquid penetrant methods. The preferred test medium consists of a suspension of dyed soHd particles, which may be contained in a Hquid vehicle dyed with a different color. Test indications can form wherever suspensions can enter cracks and other discontinuities open to the surface and be absorbed in porous material along interior crack walls. The soHd particles that form test indications ate removed by filtration along the line of the crack at the surface where they form color or fluorescent indications visible under near-ultraviolet light (1,3). 

Vitamin is iasoluble ia water and is soluble ia 70% alcohol, cbloroform, petroleum ether, ben2ene, and hexane. Vitamin is stable ia air but should be protected from light. Although unstable ia alkaU, the vitamin is stable ia acidic medium. Its facile decomposition ia basic solution forms the basis of the Dam-Karrer color test. 

Thus, the dermal nitrate test is a color test for unbumed or partially burned gunpowder, ie, nitrocompds, which form a blue product with the acidic diphenylamine reagent... 

Cocaine drug testing kits either manufactured for law enforcement purposes or produced by the underground. These testing kits are simply presumptive color tests. The basic color test used for cocaine is cobalt thiocyanate. The cocaine or any of the other substances from the caine family will form a brilliant blue flaky precipitate in the cobalt thiocyanate. This is an indication that the product is cocaine, procaine, tetracaine, etc. In order to determine whether there is actually any cocaine and not all procaine, stannous chloride is added to the precipitate causing all of the caines except cocaine to dissolve. 

A sample is tested for the presence of the Hg22+ ion. This ion, along with others, may be precipitated with chloride ion. If Hg22+ is present in the chloride precipitate, a black color will form upon treatment with aqueous ammonia. The balanced net ionic equation for the formation of this black color is ... 

A simple, fast and specific color test for urea nitrate was reported recently by Almog et al. It is based on the reaction between urea nitrate and ethanolic solution ofp-dimethylaminocinnamaldehyde (p-DMAC) (9) under neutral conditions [91]. A red pigment is formed within 1 min from contact. Its structure has also been determined by the same group, by X-ray crystallography [92]. It appears to be a resonance hybrid between a protonated Schiffbase (10) and a quinoid system (10a) (Eq. (14)). The limit of detection on filter paper is 0.1 mg/cm. Urea itself, which is the starting material for urea nitrate, does not react with p-DMAC under the same conditions. Other potential sources of false-positive response such as common fertilizers, medications containing the urea moiety and various amines, do not produce the red pigment with p-DMAC. 

These short-term tests can be utilized to quickly determine whether distillate fuel has a tendency to degrade in color and form deposits upon storage and use. Although... 

Konovaloff Reaction. A color test for primary or secondary nitro-compds. Samples are treated with Na hydroxide soln, the salt formed is extrd with w, and ether is added to this extr. Upon dropwise addition of ferric chloride, a red to reddish-brown color develops in the ether... 

B. o-Phthalaldehyde. The a,a,a, a -tetrabromo-0-xylene (344-370 g.) obtained as described above, part A, is placed in a 5-1. round-bottomed flask with 4 1. of 50% (by volume) ethanol and 275 g. of potassium oxalate. The mixture is heated under reflux for 50 hours (a clear yellow solution is formed after 25-30 hours). About 1750 ml. of the ethanol is then removed by distillation (which is stopped before the product begins to steam-distil), and 700 g. of disodium monohydrogen phosphate dodecahydrate (Na2HP04-12H20) is added to the aqueous residue. The mixture is steam-distilled rapidly (Note 4), using an efficient condenser, until 10-12 1. of distillate is collected and the distillate no longer gives a black color test for o-phthalaldehyde 8 when a portion is treated with concentrated ammonium hydroxide fol-... 

The test consists of warming a sample with phenol in concentrated sulfuric acid to give an intensely colored solution (usually dark red). The test solution is then diluted with water and treated with an excess of potassium hydroxide. A blue color is formed when a nitroso compound was present in the sample... 

Analyst 91(1082), 366-67(1966) CA 65, 3659(1966) (For detection of dinitro- and trinitro- aromatic bodies in industrial blasting expls, a 5—10 mg sample of expl to test is placed on a spot plate, and a drop of Me2CO-EtOH and a drop of 25% aq Me 4NOH. soln are added. The formation of a blue color indicates the presence of 2,4-DNT while 2,4,6-TNT gives a dark red color. A slight yellow color is formed initially with NG. If NG 2,4-DNT are both present, a green color is initially obtd. None of the other common components of blasting expls interfered. It is not indicated in CA which color is produced by m-MNT)... 

Detection and Determination of Starch.—(a) Qualitative test. A freshly-cut surface of the sample is treated with a few drops of iodine solution to see if a blue coloration is formed. If the result of this test is doubtful, a quantity of the dry, defatted substance is triturated well with a little water, and after depositing for a short time, the turbid liquid examined under the microscope. A little iodine solution is then added and the sped-men again examined microscopically for stained starch granules. 

With potash (Liebig). A mixture of equal volumes of the alcohol to be tested and 20% potassium hydroxide solution is gradually heated in a test-tube to boiling. Pure alcohol is scarcely coloured, whereas in presence of smaller or larger amounts of aldehydes, a yellow or reddish brown coloration is formed. 

Colors of adsorbed Hammett indicators can be used to bracket the H0 of a solid surface in the same way that the colors of more conventional acid-base indicators are used to bracket the pH of an aqueous solution. Thus, when an acid color is observed for the adsorbed indicator, the H of the solid surface is equal to or lower than the pKa of the indicator. As an example, a solid surface that has an H0 that lies between + 1.5 and -3.0 gives an acid color with benzeneazodiphenylamine (with a pKa of + 1.5) and a basic color with dicinnamalacetone (pKa of - 3.0). Color tests are made by adding 3-5 ml of dry solvent (e.g., benzene) to roughly 0.1 g of dried, powdered solid in a test tube, adding a few drops of a 0.1% solution of indicator in benzene, mixing the resulting suspension, and noting the color formed on the powdered solid. 

The second property in particular distinguishes indicator dyes from colorforming reagents. The latter are widely used in reactions in which colors are formed by chemical or biochemical (mostly enzymatic) reactions between the analyte and added reagents. These reactions are widely used in analytical and diagnostic test kits but are normally not reversible. 

There are a number of well-known tests for carbohydrates which depend on color formation. Thus in the Molisch test the substance is treated with mineral acid in the presence of a-naphthol and a characteristic purple color is formed. In Seliwanoff s test only ketoses give an immediate red color when warmed with mineral acid and resorcinol, and similarly ketoses give a blue coloration when warmed with sulfuric acid and diphenylamine in the Ihl-Pechmann reaction. 

Range finding. (If time is limited, this portion of the experiment should be performed in advance by an assistant.) In order to conduct the subsequent experiments under conditions that will yield valid assays, it is necessary to determine the amount of enzyme that will give a response proportional to the enzyme activity and within the range of the carbamyl aspartate color test. This corresponds to an amount of enzyme that forms about 0.05 to 0.10 /nmol of carbamyl aspartate when 100 pi of a suitable dilution is assayed under standard assay conditions. Because the activity of your extract will depend on a number of variables, you must assay 25-, 50-, 75-, and 100-/U.1 samples of a series of dilutions of the extract in 0.08 M sodium phosphate buffer, pH 7.0, to determine the appropriate enzyme level for use in the subsequent experiments. Suggested dilutions are 1 to 5,000, 1 to 8,000, and 1 to 10,000. 

Other ee assays have been described, although in several cases the actual degree of throughput was not specified [10]. These systems include assays based on color tests [8,46 - 48,60], IR-thermography [49,61], circular dichroism [62], fluorescence [63], and even special forms of gas chromatography [64], Moreover, optically active compounds capable of enantioselective recognition of chiral substrates can be used as... 

A few drops of a 10 per cent solution of the base in dilute hydrochloric acid is plac ed on a filter paper, and 1 drop of the solution under test is added. In the presence of nitrite, an unstable blue coloration is formed. The reagent is somewhat less sensitive than starch-iodide, but is usable even in strongly acid solutions. 

In many applications ultramarine blue is stable to around 400 °C, violet to 280 °C and pink to 220 °C. All have excellent light fastness with a 7-8 rating (full and reduced shades) on the International Blue Wool Scale. Color fade attributed to light exposure or moderate heat is almost always caused by acid attack. Ultramarines react with all acids, and if there is sufficient acid, the pigment is completely decomposed, losing all color, to form silica, sodium and aluminum salts, sulfur, and hydrogen sulfide. Evolution of hydrogen sulfide with acids is a useful test for ultramarine. 

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