Colorimetric tests

Some specific organofunctional silanes can be analyzed via colorimetry with suitable reagents. Examples include epoxysilane with bromothymol blue/thiosulfate solution methacryloxy andvinylsUanes with permanganate salts amino/diamino silanes with ninhydrine [33]. The results are semiquantitative within the same system of mineral and silane in all other cases, they are only of qualitative nature. 

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Reagents, Indicators, and Solutions. This section includes the specifications and testing methods for reagents to be used in the tests specified in the USP-NF, and directions for making the various indicator, buffer, colorimetric, test, and volumetric solutions used in the testing. Reagents for which ACS specifications exist are referenced to the ACS book (7). 

Nitrogen oxide sampling is simpler. This gas is drawn into an evacuated sample flask containing dilute sulfuric acid and hydrogen peroxide. The flask is shaken and allowed to stand for 16 h before the flask pressure is measured. Then the solution is made alkaline, and the nitrogen oxides are deterrnined by the phenoldisulfonic colorimetric test. 

Spectroscopic methods such as uv and fluorescence have rehed on the polyene chromophore of vitamin A as a basis for analysis. Indirectly, the classical Carr-Price colorimetric test also exploits this feature and measures the amount of a transient blue complex at 620 nm which is formed when vitamin A is dehydrated in the presence of Lewis acids. For uv measurements of retinol, retinyl acetate, and retinyl palmitate, analysis is done at 325 nm. More sensitive measurements can be obtained by fluorescence. Excitation is done at 325 nm and emission at 470 nm. Although useful, all of these methods suffer from the fact that the method is not specific and any compound which has spectral characteristics similar to vitamin A will assay like the vitamin... 

Identifications in terms of gas chromatographic responses, infrared data, and colorimetric tests... 

ALA and PBG can also be measured in urine by appropriate colorimetric tests. 

Alkalinity is measured by acid-base titration with methylorange or phe-nolphthalein as indicator. Phenolphthalein changes color at pH 8.3, whereas methylorange changes color at pH 4.3. At pH 8 the neutralization of the strong alkali ingredients like NaOH is essentially complete. Further reduction of the pH to 4 will also measure carbonates and bicarbonates. Colorimetric tests and glass electrode systems are used to determine pH. 

Recently a colorimetric test for methoxychlor residues was proposed by Fairing (27). The methoxychlor sample is treated with alcoholic potassium hydroxide, the reaction product is extracted with ether, the ether is removed, and the residue is treated with concentrated sulfuric acid. An intense cherry-red color is developed. No other insecticide has been found to interfere, and the reaction is sensitive to about 5 micrograms of methoxychlor. 

Dimalone [bicyclo-(2.2.1)-5-heptene-2,3-dicarboxylic acid dimethyl ester] and Octa-cide 264 [the V-octyl imide of bicyclo-(2.2.1)-5-heptene-2,3-dicarboxylic acid] do produce a red color with an absorption maximum in the same region as that obtained in the analysis of Compound 118. However, because Dimalone is an insect repellent and Octacide 264 is a pyrethrum synergist, neither of these products is likely to be encountered in commercial mixtures of Compound 118. The response to the colorimetric test for Compound 118 of some chemicals commonly used for insect control is listed in Table V. 

Ruggieri (56) reported a colorimetric test using 2-naphthoquinonesulfonate sodium to form a rose-violet color. 

Table 9 lists a number of colorimetric tests which have been used as identity tests for neomycin. No one test, however, has been demonstrated to be specific for neomycin and it is thus also advisable to establish the absence of other chemically similar antibiotics by suitable means. 

The reactivity of NO with O2 is dramatically affected upon coordination of one of the diatomic components to a metal center. For example, the second-order reactions of NO with oxyhemoglobin, Hb(02) and oxymyoglobin, Mb(02) (e.g. Eq. (47)) are quite fast and have been used as colorimetric tests for NO (105). The nitrogen product is NO3 rather than N02 that is the product of aqueous autoxidation (106). While the reaction of 02 with nitrosyl myoglobin Mb(NO) (Eq. (48)) might superficially appear similar it is much slower and follows a different rate law (107). Possible mechanisms will be discussed below. 

Colorimetric tests have the drawbacks that they are not specific for a particular substance, and false positives can be drawn due to the presence of coloured humic contaminants. In the current project, we have used on-site colorimetric methods both to identify hot spots of contamination, and to select samples for laboratory analyses. 

Thus, because the test can be carried out on 96-well microtiter plates, high throughput is possible. Of course, the inherent disadvantage noted above for some of the colorimetric tests also applies here, namely, the fact that the optimization of a potential catalyst is focused on a specific substrate 11 modified by incorporation of a probe, in this case the fluorogenic moiety 14. However, one can expect the test to be useful in directed evolution projects in which proof of principle is the goal. Moreover, this kind of approach can be used in very practical applications, namely as a pre-test for the activity of enzymes. 

The total free chlorine in wastewaters as measured by colorimetric techniques constitutes both the dissolved molecular chlorine, hypochlorite ion, OCl, and hypochlorous acid. An equilibrium exists between these species, the concentrations of which depend on the temperature and pH of the waste-water. Concentration of the hypochlorous acid may be estimated from the K value or from the ratio (33% of the measured concentration of free chlorine). The free chlorine may be measured by amperometric titration after the addition of a phosphate buffer solution to produce a pH between 6.5 and 7.5. The sample is titrated against a standard solution of phenylarsine oxide. Alternatively, the syringaldazine (3,5-dimethoxy-4-hydroxybenzaldazine) colorimetric test may be performed. This color-forming reagent in 2-propanol yields a colored product with free chlorine, the absorbance of which may be... 

Elemental composition Na 46.92%, C 24.50%, N 28.58%. An aqueous solution is analyzed for sodium. Cyanide is measured by an electrode specific to cyanide ion. Alternatively, cyanide may be measured by pyridine-barbituric acid colorimetric test (See Hydrogen Cyanide). 

Elemental composition Na 58.93%, S 41.07%. An aqueous solution is analyzed to determine sodium content. Also, an aqueous solution may be analyzed for sulfide by methylene blue colorimetric test or by iodometric titration (APHA, AWWA, and WEF. 1999. Standard methods for the Examination of Water and Wastewater, 20 ed. Washington, DC American Pubhc Health Association). The methylene blue test is based on reacting sulfide, ferric chloride and dimethyl-p-phenylenediamine to produce methylene blue. Also, sulfide can be measured by using a sdver-sdver sulfide electrode. Quahtatively, sulfide may be identified from the hberation of H2S on treatment with acid. The H2S turns the color of paper soaked with lead acetate black (See Hydrogen Sulfide). 

A, Colorimetric Tests a) Oxidation with bromine or permanganate (p328). 

Noninitiating Explosives, General Tests (1347) Auxiliary Tests for Specific Materials RDX, Composition A-3, Comp B, Comp C, Torpex, Tritonal, Amatol, Ammonal (1347 1349). Colorimetric tests for some expls are on p 1348... 

Colorimetric tests for NGu are found in Ref 20, p C418-R, Vol 3 of Encycl under Tests for Propellants... 

Neu4,5Ac2 as the only sialic acid, as was shown by using sialidase and colorimetric tests,96 and by 500-MHz, H-n.m.r. studies.17... 

Presence of DPhA may be detected by any colorimetric tests described under Analytical Procedures (See next item)... 

Aq solns of ferric azide have a deep red coloration similar to that produced by Fe(CNS)s. This characteristic coloration is also produced when ferric salts are added to aq solns of hydrazoic acid, thus serving as a colorimetric test for HN3(Ref 3)... 

Colorimetric Tests for Explosives, Propellants and Pyrotechnic Compositions. These tests include determinations of beat of combus ioa(designated as Q ), beat of explosion(Q ), beat of formation(Qt), beat of fusion... 

To this effect, the measurement of absorbance is preceded by a chemical transformation (derivatisation) that has to be specific, total, rapid, reproducible and yield a UV/VIS absorbing derivative that is stable in solution. This is the principle of colorimetric tests. 

Bases Used in the Manufacture of Explosives and Propellants Following are a few examples of bases used in expl plants and labs a)Ca hydroxide has been used as a catalyzer in some reactions and as neutralizer of acidic wastes from plants manufg acids, TNT, etc b)Ammonium hydroxide- as a neutralizer of acidic materials and as a purifier of crude TNT(such as was practiced during WWII at the Vest Virginia Ordnance Works). Its use in chem labs is very extensive c)Na hydroxide has been used in some plants for neutralizing acidic substances. For instance, red waters(< -v) of TNT plants are neutralized and made alkaline prior to their concn in stills. Lab uses include titrations of acids manufd at the plants d)K hydroxide has been used in labs of plants for colorimetric testing of TNT and DNT, etc... 

Carbazole, Analytical Procedures, Carbazole gives with isatin in coned sulfuric acid a blue coloration(Ref 1). As an indole derivative, it gives a positive "pine-splinter test (formation of a red color when a pine-splinter soaked in HCI soln is held in the vapor of an ale soln of carbazole)(Refs la, 2 8). Carbazole may also be identified by a bluish-green coloration produced when a trace of carbazole is dissolved in coned sulfuric acid and a drop of nitric acid is then added(Ref 8,p 72). Various other colorimetric tests for carbazole are known, such as described in Refs 1,1a,2,5 6 and Addnl Refs a,e,g,h m... 

Central ite 1 Analytical Procedures. Centr 1 can be detected by various colorimetric tests, such as described in Refs 1,6,12,24, 28 Sc 33. Some other qualitative tests are given in Ref 13. Quantitative detns of Centr 1 by bromination methods are described in Refs 4,5,7,9,10,14,16,17,20,27,34 Sc 35. Chromatographic and spectrophotometric methods are found in Refs-11,15,18,21,22,23,24, 29,30,32 Sc 33. Other quantitative methods, including polarographic, are in Refs 2,7a,20a,25, 26,27 Sc 30. X-ray diffraction spectra data are given in Ref 19. Detns of stabilizing action of Centr 1 by methods of Taliani and Thomas are discussed in Refs 3 8... 

Refs l)Gody(1907), 243 4(Colorimetric tests for chlorates) 2)Escales, Chloratspr(1910), 45-8(Qualitative) 48-51(Quantitative) 51 2 (Detn of impurities in chlorates) 72-4(Tests for. chlorates in BkPdr) 3)C.G.Storm, "The Analysis of Permissible Explosives , US BurMinesBull 94(1916), 14-16 62-4 4)... 

As only traces of Amm chlorate are present in Amm perchlorate, a colorimetric test can be used, such as by means of brucine -sulfuric acid reagent(Ref 1) or by ortho -tolidine reagent(Ref 2)... 

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