Methylene Blue test

The Methylene Blue test is used to determine if there is any chemical or physical damage to the membrane surface. In this test, a sheet of membrane taken after autopsy is tested in a flat-sheet test apparatus. The feed side of the membrane is exposed to a 0.05% solution of methylene blue. If the membrane is damaged, the permeate will turn blue and the membrane will stain blue in the damaged areas. 

The Fujiwara test is used to determine whether a membrane has been oxidized by exposure to halogens. The test measures the presence of halogenated organics in a membrane sample. The test involves a small piece of membrane placed in the bottom of a test tube. One drop of 5N sodium hydroxide solution and 2 drops of a pyridine solution are added to the test tube. The tube is then placed in a water bath at about 90°C, and held there for 30 seconds. A positive test occurs when the pyridine layer in the test tube shows a red or pink color. Note that prolonged heating of the sample will cause the color to fade or turn to brown/yellow.7 

The methylene blue test is used to determine the quality of fines by ascertaining the existence of active clay minerals. In contrast with inactive clay minerals, active clays tend to swell depending on their water content. This swelling has a detrimental impact on both the bituminous mixture and the unbound layers of the pavement. 

The test is based on the adsorption principle of clay minerals using methylene blue dye. During the test, the quantity of methylene blue required to cover all clayey ingredients is measured. The quantity of methylene blue dye adsorbed is related to the specific surface of the clay mineral (montmorillonite, illite and kaolinite). Active clay minerals have a large specific surface in contrast to inactive clay materials. As a result, the required methylene blue quantity will be proportional to the quantity and the type of clay minerals. 

The methylene blue test is supplementary to the sand equivalent test, since the latter determines only the existence of clay particles and not the presence of active clay minerals. In some countries, the methylene blue test has replaced the sand equivalent test. 

The methylene blue value (MB) of the 0/2 mm fraction, expressed in grams of dye per kilogram, is determined from the following relationship  

In the case a fraction 0/0.125 mm is used, the result is marked as MBp. In both cases, the methylene blue value is recorded to the nearest 0.1 g/kg. 

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The methylene blue test can also be used to determine cation exchange capacity of clays and shales. In the test a weighed amount of clay is dispersed into water by a high-speed stirrer. Titration is carried out as for drilling muds, except that hydrogen peroxide is not added. The cation exchange capacity of clays is expressed as milliequivalents of methylene blue per 100 g of clay. 

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. 

Figure 14.16 Methylene Blue test showing stained permeate side of a membrane, indicating damage to the membrane.

Foaming agents or detergents are used as indicators of undesirable pollutants such as sewage. They are measured by the methylene blue test (Table 13.8). 

Methylene blue test p-Aminodimethylaniline is converted by iron(III)... 

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. 

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. 

Amphoteric surfactants contain both anions and cations. They should show positive results when tested using either the basic methylene blue test for anionic surfactants or the alternative bromophenol blue test for cationic surfactants. 

Part 9 Assessment of fines — Methylene blue test... 

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 ... 

The tests used are (a) the determination of fines content, (b) the sand equivalent test conducted on fine aggregates and (c) the methylene blue test conducted when the fines content is greater than 3%. 

Methylene blue tests for determining both MB and MBp values have been carried out on various rocks (Nikolaides and Manthos 2007). The results obtained are shown in Figures 2.2 and 2.3. 

CEN EN 933-9. 2009. Tests for geometrical properties of aggregates - Part 9 Assessment of fmes-Methylene blue test. Brussels CEN. 

ISSATB 145.1989. Test method of methylene blue test adsorption value (MBV) of mineral aggregate fillers and fines. Washington, DC ISSA. 

Resazurin test The resazurin test is much quicker than the methylene blue test. Milk is mixed to aerate it and 10 ml placed in a tube. Resazurin dye solution (made from a standard tablet) is added, the tube sealed, inverted twice, and incubated at 37.5 C for 10 min. If actively reducing bacteria are present, the... 

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