Acidic methylene blue test

The test is conducted as in Section 4.3.1, acidic methylene blue test. If the aqueous layer is emulsified to a milk-like state, or both layers have the same colour, the existence of non-ionic surfactants can be confirmed. 

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). 

MarshallfRef 2,pp 155—6) stated that nitration of hydrocellulose with mixed acid contg HN03 42.03, HaS04 46.22, Ha O 11.50 and N204 0.25% gave a product contg about 13.3% N. Its soly in ale was 12.15% and its methylene-blue test(mg absorbed by lg of nitrated product) was 2.4 Refs l)Beil — not found 2)Marshall 1... 

Many anionic surfactants can react with a cationic dye such as methylene blue to form strong ion pairs that can be extracted by a suitable organic solvent and can be determined using colorimetric techniques. The anionic surfactants that respond to the methylene blue test are primarily the sulfonate (RS03 Na+) and the sulfate ester (R0S03 Na+) type substances. On the other hand, soaps and the alkali salts of fatty acids (C-10 to C-20) used in certain detergents do not respond to the above test. The various anionic surfactants and their characteristic structural features are presented in Figure 2.32.1. 

Methylene Blue test can also be used to differentiate between oxycellulose and hydrocellulose. Methylene Blue is a cationic dye. Standard cellulose generally has no affinity for Methylene Blue, but oxycellulose with the formation of carboxyl groups confer an affinity and can be sorbed onto cotton. For this purpose. Methylene Blue absorption tests are carried out both at pH of 7.0 and at a pH of 2.7 (acidic). Two pieces of fabrics to be tested are taken and treated one with Methylene Blue at a pH of 2.7 and the other at pH 7.0. If oxycellulose is present, the material will absorb less dye in the acid than in the neutral solution, whilst reverse is the case if hydrocellulose is present. The degree of staining will indicate the extent of degradation. 

Methylene blue test 7V7V-Dimethyl-p-phenylenediamine is converted by iron(III) chloride and hydrogen sulphide in strongly acid solution into the water-soluble dyestuff, methylene blue ... 

MBAS value (72). The so-called interference-limited methylene blue test is also likely to return high values when used for unpolluted samples. The MBAS method is discussed in Chapter 12. For routine wastewater analysis, the determination is frequently automated by use of flow injection analysis. The LAS degradation product sulfophenylcarboxylic acid will contribute to the MBAS response if the alkyl chain length is greater than 6 carbons. Dialkyltetralin-and dialkylindanesulfonates are also presumed to be MBAS-active (35). There are many variations of the methylene blue method used by various regulatory agencies. These differ mainly in the amount of effort expended to eliminate interferences (73). 

The presence of chloride, nitrate, sulfide, organic sulfonates, cyanates, organic amines, and particulate matters may interfere in the test. The two major interferences, chloride and nitrate, however, may be removed in the acid backwash steps. Sulfide reacts with methylene blue to form a colorless complex. Interference from sulfide may be removed by treating the sample with a few drops of 30% H2Oz, whereupon sulfide converted into sulfate. 

To check for organic-soluble peroxides, add several milliliters of the methylene chloride solution to a solution containing ca. 1 mg of sodium dichromate, 1 mL of water, and 1 drop of dilute sulfuric acid. A blue color in the organic layer is a positive test for perchromate ion. The checkers found that the combined organic phases exhibited a positive test and therefore stirred them overnight with a solution of 100 g of sodium metabisulfite in 500 mL of water prior to drying. 

Add -5 ml of 1 % sample surfactant solution into a mixture of 10 ml methylene blue solution and. 5 ml chloroform in a test tube shake vigorously then allow it to stand until two layers are formed. If the chloroform layer (bottom layer) shows blue, add another 2-3 ml of the surfactant solution. Shake well and leave for layers to form. The chloroform shows as dark blue and the water layer is almost colourless. This is a positive result of the existence of anionic surfactant in the sample solution. This test is suitable for alkylsulphate and alkylbenzolsulphonate surfactants. Soap cannot be tested because it would precipitate in the strong acidic medium. 

With these possibilities in mind we attempted the photo-oxygenation of norbornene. With either methylene blue or hematoporphyrin as sensitizer and methanol or pyridine as solvent, we obtained no evidence of any reaction by infrared or NMR spectrum, by gas chromatography, or by spot test for hydroperoxide (potassium iodide/starch in 2-propanol/ acetic acid) or peroxide (hydriodic acid/starch in 2-propanol). While the half-life of reaction of cyclohexene was only about one day under our reaction conditions, no evidence of reaction of norbornene was obtained in a period of one month. Assay of norbornene by gas chromatography with benzene as internal standard failed to show any depletion of norbornene over the attempted reaction interval. 

A colourimetric method was developed for determination of allyl isothiocyanate, with a detection limit of ca 1 g S. It is based on alkaline hydrolysis to yield sulphide ions, which subsequently react (as shown in equation 40) to yield methylene blue, which in turn is measured at 665 nm. The following sulphur-containing compounds were tested as possible interference with the method Thioacetamide, thiourea, cysteine, methionine, cysteic acid. 

In addition to the iodometiic determination, direct precipitation as barium sulfate before and after treatment with bromine was suggested for both quantitative and qualitative test for sulfur dioxide in wine (see Monier-Williams, 1927). Precipitation of SO2 after oxidation with H2O1 as the benzidine sulfate was proposed by Rothen-fusser (1929) reduction of the molybdenum in phosphomolybdic acid by the sulfite ion present in an aqueous solution of the food was proposed by Sasaki (1928) as a colorimetric method formation of a blue color from a solution of 1% methylene blue and 5% iodine in potassium iodide was proposed by Svershkov (1939). Mathers (1949) proposed a turbidimetric method based on the distillation of wine into a dilute solution of lead acetate to form a colloidal suspension of lead sulfite whose spectral transmittance in the range of 400 to 700 mn could be used as a measure of sulfur dioxide. This is similar to turbidimetric methods based on turbidity produced by adding BaCfii to a... 

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