Dimidium bromide

Herring Dimidium bromide + disulfine blue 2 Hyamine 1622 183... 

The two-phase titration is based on the reaction of anionic surfactants with cations—normally large cationic surfactants—to form an ion pair. The preferred cationic is benzethonium chloride (Hyamine 1622, 1) because of the purity of the commercially available product. On neutralization of the ionic charges, the ion pair has nonpolar character and can be extracted continuously into the organic phase, e.g., chloroform, as it is formed. The reaction is monitored by addition of a water-soluble cationic dye, dimidium bromide (2), and a water-soluble anionic dye, disulfine blue (3). The cationic dye forms an extractable... 

Recently, several modifications of the two-phase titration and their precisions have been compared. The two-phase titration with the above-mentioned mixed indicator system, dimidium bromide/disulfine blue, is standardized in DGF (Deutsche Gesellschaft fur Fettforschung) and DIN methods, and is less time consuming and simpler than the standard gravimetric and extraction methods [18]. 

Gravimetric and volumetric methods are practicable for the quantitative determination of the a-sulfo fatty acid esters. Using gravimetric methods the surfactant is precipitated with p-toluidine or barium chloride [105]. The volumetric determination method is two-phase titration. In this technique different titrants and indicators are used. For the analysis of a-sulfo fatty acid esters the quaternary ammonium surfactant hyamine 1622 (p,f-octylphenoxyethyldimethyl-ammonium chloride) is used as the titrant [106]. The indicator depends on the pH value of the titration solution. Titration with a phenol red indicator is carried out at a pH of 9, methylene blue is used in acid medium [106], and a mixed indicator of a cationic (dimidium bromide) and an anionic (disulfine blue VN150) dye can be used in an acid and basic medium [105]. 

BASIS OF MANUAL PHOTOMETRIC TITRATION. The determination of anionic surfactants by a photometric titration employs a cationic indicator to form a coloured complex with the surfactant which is insoluble in water but readily soluble in chlorinated solvents (1 ). The end point of the titration occurs when there is a loss of colour from the organic phase. A considerable improvement in this technique is achieved by the use of a mixture of anionic and cationic dyes (4 ), for example disulphine blue and dimidium bromide (Herring s indicator (3)). The sequence of colour changes which occurs during the two phase titration of an anionic surfactant (AS) with a cationic titrant (CT) using a mixed indicator consisting of an anionic indicator (AD) and cationic indicator (CD) is summarised in Scheme 1 ... 

The titration end-point is registered with a suitable indicator, which plays an important role in the titration process. A variety of indicators has been described in the literature [31,36], An example of an effective indicator used in two-phase titration is a mixture of anionic dyestuff, disulfine blue VN, and cationic dyestuf, dimidium bromide, the structures of which are shown in Fig. 11-32 (b,c). 

Let us describe the mechanism of two-phase titration in some detail, using the titration of sodium dodecylsulfate (SDS) with Hyamine 1622 in the presence of mixed dye indicator as an example. At the beginning of the titration, when only SDS is present in aqueous solution, dimidium bromide reacts with it to form a salt that is insoluble in water, but... 

Fig. 11-32. Chemical structures of reagents frequently used in two-phase titration the titrant, Hyamine 1622 (a) components of mixed indicator, disulphine blue VN (b), dimidium bromide (c)...

Many amphoteric surfactants at acidic pH behave like cationic ones, so they can be determined by the standard two-phase titration method using dimidium bromide/disulfme blue VN mixed indicator. Precise analysis can, however, be difficult due to the formation of emulsions in the vicinity of the end-point. These problems can be minimized by reversing the titration, i.e., using amphoteric surfactant as a titrant, and by adding ethanol. 

For anionic surfactants colorimetric methods utilize the formation of an ion pair between the surfactant anion and a cationic dye. Similarly to two-phase titration, colorimetric determination is based on the fact that the ion pair is extractable into organic solvent, while the dye by itself is not. A characteristic example of the analysis of anionic surfactant is the determination of alkylsulfates and alkyl(aryl)sulfonates as their complex with methylene blue extracted into chloroform [31]. The absorbance of chloroform extract is measured at 625 nm versus chloroform background. This methods allows one to analyze alkylsulfates and alkyl(aryl)sulfonates separately. Alkylsulfates, in contrast to sulfonates, are easily hydrolyzed by hydrochloric acid. The products of hydrolysis do not interact with methylene blue and are not transferred into chloroform. Some other cationic dyes, such as dimidium bromide, can also be used. In fact, the use of the latter allows one to achieve much higher sensitivity than that obtained with methylene blue. 

SANS curves obtained after subtraction of the cell+C02 background are shown in Figure 4b. Data fitting with the model in ref. 37 was consistent with "dry" reversed micelles, as observed with these surfactants in n-heptane solvent (86). UV-vis dye solubilisation measurements shown in Figure 4c also provide evidence for aggregation. If reversed micelles were present the positively charged chromophore, dimidium bromide (A 550 nm), should be... 

Figure 4. (a) Surfactants AOT (AerosoUOT) Sodium bis (2-ethyl-l-hexyl)sulfosuccinate, surfactant A (sodium bis (2,4,4-trimethyl-1-pentyl)sulfosuccinate) and surfactant B (sodium bis (3,5,5-trimethyl-1-hexyl) sulfosuccinate. (b) SANS data obtained after subtracting the cell sc-C02 background for surfactant K as a function of concentration at 0.15 ( ) and 0.10 (O) mol dm . T - 32X1 and 500 bar. The fits are to a polydisperse sphere model with = 14 1A and = 0.20 (footnote 37). (c) UV-vis spectrum of dimidium bromide dispersed in SC-CO2 with reversed micelles of surfactant B at 40X1 and 500 bar. The surfactant concentration is 0.025 mol dm. Reproduced with permission from Journal of the American Society, 2001, 123, 988-989. Copyright 2001 Am. Chem. Soc. 

The classification is done by adding 1 ml of the mixed indicator (disulphine blue V and dimidium bromide) to two small portions of a solution of the surfactant, one acid and the other alkaline, adding a few... 

The method uses a mixed indicator containing disulphine blue VN (Colour Index 42045, also known as Acid Blue 1), which is anionic, and dimidium bromide, which is a pink cationic dye. 

A solution of the sample is placed in the titration vessel, mixed indicator and chloroform are added and the two-phase mixture is shaken or stirred. The pink cationic indicator dimidium bromide ( Dm Br" ) reacts with the anionic surfactant ( An ) and the reaction product is extracted by the chloroform, colouring it pink. 

Further increments of cationic titrant react with the anionic indicator disulphine blue VN (Acid Blue 1, AB" , to avoid confusion with Dimidium Bromide). The salt is extracted by the chloroform layer and colours it blue. This indicates that the end-point has been overshot. 

Indicator weigh 0.5 g disulphine blue VN and 0.5 g dimidium bromide in two 50 ml beakers. Add 25 ml hot 10% aqueous ethanol to each and stir until dissolved. Transfer both solutions to a 250 ml volumetric flask, dilute to volume and mix. This is the stock solution. Place 200 ml water and 20 ml stock solution in a 500 ml volumetric flask, add 20 ml 2.5 M sulphuric acid, dilute to volume and mix. This is the acid mixed indicator. 

Add 10 ml water, 15 ml chloroform and 10 ml acid mixed indicator (disulphine blue VN and dimidium bromide). 

C20H21CIN2O4, Dimethyl-1-p-chlorophenyl-3,4-propano-4,5,6,7-tetra-hydroindazol 5,5-dicarboxylate, 46B, 280 C20H21NO4, Dimethyl 4,5,10,11,12,12a-hexahydroindolo[1,7-cd]benz-azepine-7,8-dicarboxylate, 44B, 260 C2oH22BrN30, Dimidium bromide, 40B, 278... 

Bemegride Sodium, B.Vet.C. Chlorpropamide Chlorthalidone Crotamiton, B.P.C. Dichlorphenamide Dimidium Bromide, B.Vet.C. Dinazine Aceturate... 

Most of the compounds listed above can be determined by Method A (see p. 449) in some cases e.g. dimidium bromide) it is essential to use potassium rather than sodium sulphate for quantitative decomposition where the substance is a salt of a halogen acid it should be heated for fifteen minutes with the nitrogen-free concentrated sulphuric acid before addition of the mercury. 

Volumetric methods are the traditional methods employed in routine controL specifically two-phase titration for anionic and cationic surfactant determination, and are characteristically highly sensitive. They are based on the reaction between an anionic surfactant and cationic surfactant (one of which is a sample surfactant and the other a titrant surfactant) in a two-phase system (chloroform-water). The endpoint is detected by a transfer-phase indicator, the most common of which is a mixture of dimidium bromide and disulfine blue although methylene blue (Epton method), which is the first indicator chronologically, is also applied. Two commonly used titrants are sodium lauryl sulfate for cationic surfactants and benzethonium chloride, currently named Hyamine 1622, for anionic surfactants. 

A mixture of anionic surfactants (salts of fatty acids (currently named soaps), alkyl sulfates and alkyl sulfonates may be determined by three titrations. These three surfactants are titrated using dichlorofluorescein as indicator a dimidium bromide and disulfine blue mixture are used for titration of alkyl sulfates and alkyl sulfonates, while disulfine blue is used for alkyl sulfonates titration after acid hydrolysis (Cozzoli, 1993). 

Watkins, T. I. Trypanosides of the phenanthridine series. Part I. The effect of changing the quartemary grouping in dimidium bromide. J. Chem. Soc. 1952,... 

Another scheme calls for adjusting two surfactant aliquots to pH 1 and pH 11, respectively. The solutions are mixed with chloroform and treated with the mixture of two indicators used in two-phase titration (Chapter 16), dimidium bromide and disulfine blue. If only soap is present, the chloroform phase will be colorless at low pH and red at high pH other anionics will show the pink color in the chloroform phase at each pH. Quaternary amines will color the chloroform phase blue at either pH, while other amines will only yield the blue color at low pH nonionics show no color. Obviously, mixtures of surfactants will give confused results (27,30). 

Mixed indicator solution is prepared by dissolving separately 0.5 g dimidium bromide and 0.25 g disulphine blue in warm 10 90 ethanol/water. Mix and make up to 250 mL with 10 90 ethanol/water. Transfer 20 mL of this solution to a 500-mL volumetric flask, add 50 mL 1 N H2SO4, and dilute to volume with water. 

Notes (a) In letters to several journals during 1995-1996, Professor Norbert Busch-mann suggested that dimidium bromide may have mutagenic properties and that its solutions should therefore be handled with all appropriate precautions, (b) Mettler has developed titration accessories which allow this analysis to be performed automatically (10). 

A modification of two-phase titration calls for preparing only one titration system for both cationics and anionics the benzethonium chloride, disulfine blue/dimidium bromide method which is standard for anionics. For the determination of cationics, an excess of standard sodium dodecylsulfate is added, and the excess determined by titration with benzethonium chloride (31). 

Acid mixed indicator solution To a 250-mL volumetric flask add 0.050 g dimidium bromide dissolved in 15 mL hot 10 90 EtOH/H20 and 0.050 g disulphine blue V which has been dissolved in 10 mL hot 10 90 EtOH/H20. Add about 100 mL water and 10 mL 2.5 M H2SO4, then dilute to volume with water. Store protected from light. 

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