Disulphine blue

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 ... 

This is used as a levelling agent with many acid dyes. The effect of Glauber s salt on the distribution of Disulphine Blue V between the fibre and the solution is shown in Table 15.2 (Vickerstaff, loc. cit.). 

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)...

Quite drastic conditions are required to desorb cationic surfactants from solids. Extraction with methanolic HCl resulted in optimum recovery. However, the extract has to be purified by extraction into chloroform in the presence of disulphine blue or LAS. Einally, cleavage of the ion pairs is done on ion exchangers. Hellmann used an AI2O3 column to purify sewage sludge extracts. In this way, he was not only able to separate impurities but also to elute cationic and anionic surfactants stepwise with different solvent systems. 

Cationic surfactants form ion pairs with suitable anionic dyes that are extractable into organic solvents. The anionic dye most widely used is disulphine blue. After extraction of the ion pair into chloroform the extinction is determined at 628 nm. The presence of anionic surfactants results in serious interferences, and therefore they have to be separated by anion exchange before the addition of disulphine blue. The determination of cationic surfactants is hampered by some problems not encountered with MBAS. In particular, cationic surfactants are strongly adsorbed to almost any surface, so that all apparatus has to be specially pretreated. 

Physical interferences often arise when the test compound or metabolite has the same color as the endpoint color of the reaction used to measure the analyte. Any compound that imparts an unusual color to blood or urine may cause interference, depending on the analytical technology (e.g., disulphine blue) (Halloran and Torrens... 

Halloran, S. R, and D. J. Torrens. 1983. Effects of the drug disulphine blue on routine biochemical investigations. Annals of Clinical Biochemistry 20 317-320. 

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. 

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). 

Disulphine blue VN150 solution is prepared by dissolving 0.16 g of the dye in 250 mL 90 10 water/ethanol. 

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. 

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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