Indophenol test

The Gibbs indophenol test is useful for the identification of phenol in phenolic resins and in substances that split off phenol or phenol derivatives on heating. Polycarbonates or epoxy resins as well as some HT-thermoplastics are examples of this. Heat a small sample for a maximum of 1 min in a pyrolysis tube and cover the opening of the tube with a piece of prepared filter paper. To prepare the paper, drench it in a saturated ether solution of 2,6-dibromoquinone-4-chlorimide and then air-dry it. After the pyrolysis, hold the paper over ammonia vapor or moisten it with 1 - 2 drops of dilute ammonia. A blue color indicates phenol (cresol, xylenol). 

Almost all polycarbonates used as plastics contain bisphenol A. For positive identification, the color reaction with p-dimethylaminobenzaldehyde (see Section 6.1.2) or the Gibbs indophenol test (see Section 6.1.3) is used. 

Additional information can be obtained from certain special tests. Thus, the Gibbs indophenol test is positive with PEEK, PAR, and PEI (see Section 6.1.3). Using the color reaction with jo-dimethylamino benzaldehyde (Section 6.1.2), one can differentiate HT-polyamides, such as PA 6-3-T, from polymers that develop phenolic decomposition products during pyrolysis. While with polyamides, the red coloration obtained after the addition of concentrated hydrochloric acid remains, with polycarbonates it turns blue. 

Free phenol n. The uncombined phenol existing in a phenolic resin after curing, the amount of which is indicative of the degree of cure. The presence of such free phenol can be detected by the Gibbs indophenol test. 

Add 1-2 ml cone. H2SO4 to a small amount of the sample taken in a test tube. Then add about 1 ml cone. HNO3. Carefully add down ie sides of the tube an aqueous solution (5% w/v) of NaOH so as to form a separate layer at the top of the acid solution. A red colour at the interface indicate EP-(ii) EP gives a positive (blue colour) indophenol test (p. 188). 

Phosphatase Test. The phosphatase [9001-78-9] test is a chemical method for measuring the efficiency of pasteurization. AH raw milk contains phosphatase and the thermal resistance of this enzyme is greater than that of pathogens over the range of time and temperature of heat treatments recognized for proper pasteurization. Phosphatase tests are based on the principle that alkaline phosphatase is able, under proper conditions of temperature and pH, to Hberate phenol [108-95-2] from a disodium phenyl phosphate substrate. The amount of Hberated phenol, which is proportional to the amount of enzyme present, is determined by the reaction of Hberated phenol with 2,6-dichloroquinone chloroimide and colorimetric measurement of the indophenol blue formed. Under-pasteurization as well as contamination of a properly pasteurized product with raw milk can be detected by this test. 

Tests were carried out to compare the efficiency of extraction results obtained using a manual weighing and sample preparation method, and the reagent adder and sample preparation unit. Extracts of four replicates of ten soils were prepared by each method and analysed for nitrate- plus nitrite-nitrogen by a diazotisation and coupling reaction with sulphanilic acid and N-(l-naphthyl)ethylenediamine and ammonium-nitrogen by an indophenol method. These methods are described fully by Greaves et al. [48]. 

Identification A 1 10 aqueous solution gives positive tests for Calcium, Appendix IIIA, and it decolorizes dichlorophe-nol-indophenol TS. 

The XMoji-SiOj materials were tested for adsorption behaviors and three colored materials Rhodamine B, indophenol, and methyl violet were chosen. Solid porous XMo,-Si02 materials were added to the ethanol solutions of dyes. The suspension of the solution of dyes (0.02g/L) and XMo,-SiO2(0.02g) were shaken in dark for 5 days. The adsorption isotherms were obtained by detecting the changes of concentrations in upper clear solutions by 756CRT UV-VIS spectrophotometer. 

In order to test the adsorption behaviors of this kind of macroporous materials, three colored materials Rhodamine B, indophenol, and methyl violet were chosen. The changes of concentrations of the solutions of dyes in a period were detected by UV-VIS spectrometer. The adsorption isotherms are shown in Figure 6. From the adsorption isotherms we can see that the adsorption behaviors of macroporous materials are not good. The reason may be (I) that the surface areas of macroporous materials are low ca. lOOmVg) and the active sites are few (II) the solvent ethanol was adsorbed by the hybrid materials. The adsorption isotherms of three colored materials were different. Methyl violet was an alkaline indicator and the adsorption of methyl violet and hybrid materials may correspond to a chemisorption. Acid indicator Rhodamine B was not adsorbed by the adsorbent and the solvent ethanol was adsorbed instead. Therefore, after reaction the concentration of the solution increased and the adsorption capacity appeared negative. Compared with the former two, indophenol molecule is smaller and is easy to be absorbed. Therefore, its adsorption behavior is stronger relatively. 

Experiments were carried out in a 500-mL photochemical reactor with a quartz immersion well. A 10 x 20 cm2 piece of film was wrapped around the immersion well and tied in place with Teflon tape. Then 350 mL of H20 was placed in the reactor and NaOH was added to adjust the pH to 12. The system was purged continuously with air or N2 and irradiated with a 400-W medium-pressure Hg lamp. After a period of time the solution was tested for NH3 by the indophenol method, and for NOJ/NOJ (combined total nitrite and nitrate) by Cd reduction, followed by colorimetric analysis by the azo-dye method [84]. The azo-dye method, sometimes known as the Griess method or the sulfanilic acid method, has been described elsewhere [87]. 

Experiments were performed in an immersion-well reactor with a capacity of 125 mL. Here 200 mg of the putative catalyst was suspended in 100 mL of doubly-distilled water. The light source was a 125-W medium-pressure Hg lamp which produced more than 7 x 1018 photons s 1 cm-2 inside the immersion well. Irradiation was carried out under a stream of N2 which had been purified by passing it through a hot copper-pellet column, chromic acid solution, and potassium hydroxide solution. After irradiation the reaction mixture was distilled with base and the distillate was analyzed by the indophenol method. A portion of the mixture was centrifuged and analyzed for N03 by Cd reduction followed by colorimetric determination by the sulfanilic acid method (azo dye test) [89],... 

Then 200 mg of the putative catalyst was suspended in 350 mL of FI20 in a cylindrical immersion-well reactor. The pH was adjusted to 11 with NaOH, and the reactor was purged with N2 for 30 min prior to irradiation. The N2 flow rate was reduced to 10 mL min, and the reaction mixture was irradiated by a 400-W medium-pressure Hg lamp. Control experiments were performed without irradiation, or with argon substituted for nitrogen. Aliquots of solution were withdrawn at intervals and tested for N02 (azo dye test), NOj- (Cd-reduction, azo dye test), and NH3 (indophenol method). 

Gibbs indophenol See test, phenol Gibbs indo-phenol. 

In a microcrucible treat test solution with reagent (1) to reduce analyte to phenylhydroxylamine, which rearranges with acid to 2- and 4-aminophenol. Add reagent (2) to form indophenol blue... 

Basic TLC design is illustrated here with the aid of a three-component lipophilic dye mixture (Mallinkrodt dye 3082, containing 1 ig/(J.l of each dye), containing butter yellow, Sudan red G, and indophenol blue. Various other lipophilic dyes are available commercially, including four- to six-component mixtures. For further information, consult the Analtech catalog. One of Stahl s (1969) major contributions to TLC was the introduction of standard dyes to test basic TLC procedures. 

Fig. 3. Example of the performance of the apparatus. The test reaction was the reduction hy ascorbate of 2,6-dichlorophenol-indophenol, measured at 600 nm. The interval between points is 0.5 ms. The figure is redrawn from the computer output to an X-Y recorder.

Phenols with an amino group in the para position usually form indophenol dyes on treatment with phenol and sodium hypobromite. These dyes are deep blue in alkaline and red in acid solution. The test is more specific with hypobromite than with bleaching powder or calcium hypochlorite (Thorjie, Williams, and Shelswell (89)), which give a color with ammonia. 

The earliest tests used for this purpose were made with the Nadi reagent. This reagent consists of a mixture of a-naphthol and dimethyl-p-phenylene-diamine, which under the influence of certain oxidases is converted into a blue indophenol derivative. 

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