Methylene blue procedure

Because some amount of S2- may escape out as H2S during standard preparation and a small proportion may be oxidized to sulfate over a few hours, and also because methylene blue formation reaction may not thermodynamically go to completion, it is, therefore, always recommended that sulfide concentration should be determined by titrimetric iodide procedure and an average percent error of the methylene blue procedure be compared against this titrimetric procedure. 

Lew [19] has shown that 2-octadecylbutane-l,4-disulphonate is titrated by benzethonium chloride using the Epton (methylene blue) procedure, consuming 2 mol/mol. 

LAS may be determined with great sensitivity by a procedure based on extraction of the ion pair with tetraphenylpyridine into isopentyl acetate, followed by measurement of the absorbance of the extract at 305 nm (10). Interferences are similar to those discussed below for the methylene blue procedure. 

The standard procedure for the synthesis of leuco dyes related to benzoyl leuco Methylene Blue is straightforward. The one-pot synthesis is carried out in a two-phase water-toluene system. Methylene Blue is first dissolved in the aqueous phase and reduced with sodium dithionite under nitrogen and with stirring. The yellowish leuco is extracted into the organic phase where it is allowed to react with an acid chloride, the aqueous phase being made alkaline. 

Leuco Methylene Blue, Basic Blue 3, or phenazine dyes are capped with a dye bearing acid chloride or chlorocarbonyl functionality. Normal procedures employed for the synthesis of benzoyl leuco Methylene Blue can be utilized except that a dye chloroformate (69) replaces the benzoyl chloride. 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

The methylene blue reaction can also be used in a fractionation procedure for surfactants. The complexes with methylene blue can be collected in an organic solvent, concentrated, dissolved in methanol, and separated by high-performance liquid chromatography [205]. A variation of this method, permitting the collection of surfactant from large volumes of sample, should be workable in seawater. 

Where the reduction potentials of two analytes are sufficiently different a mixture may be analysed. Titanium(III), = 0-lOV may be titrated with cerium(IV) in the presence of iron(II), =0.77 V usjng methylene blue as indicator. Subsequently the total, iron plus titanium, may be determined using ferroin as indicator. The determination of iron is illustrative of some practical problems which are encountered in direct titration procedures. 

These findings lead to (he conclusion that the reduction of MHb by its reductase requires a natural cofactor, which is abolished during the purification procedure and can be replaced by methylene blue (G5, H22, H23, K8, K14). Since methylene blue and the other effective dyes are redox intermediates, it is obvious that the postulated cofactor interacts in the electron transport sequence of the MHbR reaction (H23). This is confirmed by the finding that oxygen and cytochrome c serve as well as terminal electron acceptor as does MHb (H22, H23, K14). Nevertheless, it had been possible to separate a cytochrome c reductase from MHbR in yeast extracts (A6). 

Procedure. Steam out the distillation unit for 20 min. Pipette 5 ml of ammo-nium-N standard solution into the unit. Add 7 ml of sodium hydroxide solution and steam distil the liberated ammonia into 5 ml of boric acid solution. Collect 20 ml of distillate. Add 2-3 drops of methyl red-methylene blue solution and titrate with 0.01 M sulphuric acid until the green colour changes to... 

One of the most commonly used staining procedures involves hematoxylin and eosin, but it was found that the dyes interfere with either the proteins or the MALDI process. As a consequence, the quality of the mass spectra is significantly compromised [54], When five other staining protocols (Terry s Polychrome, Toluidine Blue, Nuclear Fast Red, Cresyl Violet, and Methylene Blue) were compared to a control section (unstained tissue rinsed in 70% and 100% ethanol), Cresyl Violet and Methylene Blue had the highest degrees... 

Reduced Sulfur Compounds in Marine Sediments. To determine the applicability of the bimane-HPLC technique to measure reduced sulfur compounds in sediment porewater samples, we compared the results of the methylene blue method of Cline (26). the DTNB procedure of Ellman (28) and the bimane-HPLC procedure outlined above. Cores included came from a Spartina foliosa marsh in Mission Bay (near San Diego, California), and an evaporation pond for the production of salt in south San Diego Bay (Table I). 

All the base-specific cleavage reactions described have been used successfully for sequencing DNA. Other novel base-specific modifications have been described e.g. the piperdine-catalysed cleavage at guanine bases after U.V. irradiation in the presence of methylene blue or rose bengal and a specific thymine cleavage by piperidine treatment after reaction of the DNA with osmium tetroxide (Friedmann and Brown, 1978). These latter procedures however, have not, as yet, been widely adopted as sequencing tools. 

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