Phenolate blue developing

Ltebermann Reaction To 1 minute crystal of sodium nitrite in a clean dry test-tube add 0 5 g. of phenol and heat very gently for about 20 seconds allow to cool and add twice the volume of cone. H2S04. On rotating the tube slowly in order to mix the contents, a deep green or deep blue coloration develops (some times only after i 2 minutes). Dilute cautiously with water the solution turns red. Now add an excess of NaOH solution the green or blue coloration reappears. 

Dissolve 1 g. of the secondary amine in 3-5 ml. of dilute hydrochloric acid or of alcohol (in the latter case, add 1 ml. of concentrated hydrochloric acid). Cool to about 5° and add 4-5 ml. of 10 per cent, sodium nitrite solution, and allow to stand for 5 minutes. Add 10 ml. of water, transfer to a small separatory funnel and extract the oil with about 20 ml. of ether. Wash the ethereal extract successively with water, dilute sodium hydroxide solution and water. Remove the ether on a previously warmed water bath no flames should be present in the vicinity. Apply Liebermann s nitroso reaction to the residual oil or solid thus. Place 1 drop or 0 01-0 02 g. of the nitroso compovmd in a dry test-tube, add 0 05 g. of phenol and warm together for 20 seconds cool, and add 1 ml. of concentrated sulphuric acid. An intense green (or greenish-blue) colouration will be developed, which changes to pale red upon pouring into 30-50 ml. of cold water the colour becomes deep blue or green upon adding excess of sodium hydroxide solution. 

Recently, DeGrandpre [12] developed a probe-type sensor for the determination of PCO2 in sea water by direct immersion of the probe, which, however, has some connotations of flow-through sensor even though a pH indicator such as Phenol Red (piTj = 7.5) or Bromothymol Blue (pAn = 6.8) rather than the sample is circulated over the sensing microzone —the basic forms of these indicators have a high molar extinction coefficient at 560 and... 

For a number of years, phenolic substances were dosed by colorimetric techniques, based on redox reactions usually known as Folin Ciocalteau methods, even if a number of adjustments were developed to fit different matrix characteristics. The Folin Cioalteau reagent is a mixture of phosphomolybdic and phosphotingstic acids, with molybdenum in the 6+ oxidation state and, when the reaction takes place, it is reduced to form a complex called molybdenum blue and tungsten blue. In this complex, the mean oxidation state is between 5 and 6 and the formed complex is blue so it can be read spectrophotometrically at 750 nm. 

The most recent paper on this topic has been published by Lu and Huang (213). The method consists of an online enrichment of the aromatic amines on a carboxymethyl-bonded silica precolumn and an HPLC-UV (at 254 nm) analysis. The mobile phase, ACN-acetate buffer (pH 4.66) (40 60, v/v), was used to desorb the analytes and for the subsequent separation. The method was applied to the determination of several compounds (4-aminoazobenzene (4-AAB), benzidine (Bz), 3,3 -methylbenzidine (DMBz), 4-aminobiphenyl (4-ABP), 3,3 -dichlorobenzi-dine (DCBz), and 2-naphthylamine (2-NA) together with some substituted naphthalens and phenols) in aqueous solution of four food dyes Direct Blue 6, Amaranth, Sunset Yellow FCF, and D C Orange No. 4. Detection limits ranged between 0.6 and 1.6 fig/g. Most part of the methods developed for this kind of determination are reported in Table 3. 

There are few spectrophotometric methods published to determine ezetimibe in pharmaceutical dosage forms. The first one was established by Mishra et al. [17] by applying colorimetric assay of phenol group. This method was developed based on the reaction between Folin-Ciocalteu s (FC) phenol reagent and phenol group of ezetimibe, which results in a blue chromogen that was then observed at 760 nm. 

Postcolumn labeling is a characteristic feature of carbohydrate analysis in which no direct physical methods are available for sensitive detection. Many labeling methods have hitherto been developed. The methods with phenol in sulfuric acid [16], orcinol in sulfuric acid [17], anthrone in sulfuric acid [18], tetrazolium blue in alkali [19], copper(II)-2-2 -bicin-chonitate [20], and 2-cyanoacetamide [21] are used for photometric detection. The methods with 2-cyanoacetamide [6], ethylenediamine [22], ethanolamine [23], taurine [24], and arginine [25] are used for fluorimetric detection. Some labeling methods for electrochemical detection were reported by Honda and Suzuki in 1984 [26,27],... 

After LLE into ethanolic KOH, the antioxidant BHT (32a) used in aircraft fuel was determined in the presence of Cu(n) ions, by UVV spectrophotometry at 368 nm. Linearity was observed in the 0 to 30 ppm range, RSD <2% . A UVV spectrophotometric method for determination of -cyclodextrin (126) is based on the formation of a complex with phenolphthalein (19, Section Vin.A.3). Both the intensity and hnear range are affected by the pH and the concentration of 19 in solution. The method was considered to be inadequate for precise determinations of 126 of purity higher than 98% see also application of a-cyclodextrin (85) for analysis of phenolics in Section IV.B.4 . Phenol in the presence of sodium nitroprusside, Na2[Fe(CN)5NO], and hydroxylamine, at pH 10.26-11.46, developed a blue coloration that could be applied for quantitative analysis (kmax 700 nm, e 1.68 x 10" LmoU cm , Sandell sensitivity 0.0052 p,g phenol cm ). Beer s law was found to be valid from 0.1 to 6.5 ppm". ... 

The phenol-hypochlorite (Indophenol-blue) method was used for ammonia analysis (Solorzano, 1969). Appropriate sample sizes were fixed with phenol within 24 hours of collection (Degobbis, 1973) and stored at all times at 4 C. Analyses were made within 2 weeks of collection. The reagent dilutions given by Presley (1971) were used, but the quantity added was doubled. All reaction and color development was done in polyethylene scintillation vials. Color development was allowed for 6-8 hr to obtain a straight-line standardization curve blanks (always <0.010 absorbance with respect to distilled water, 1-cm cell) were insignificant compared to sample absorbances and precision better than 3%. Standards were diluted immediately before use. 

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