Two-phase titration with sodium dodecyl sulphate

1 Two-phase titration with sodium dodecyl sulphate 

The most generally applicable procedures are those described in the two ISO methods [1,2]. The first of these is for high-molecular-weight quats, which may be broadly defined as those containing two hydrocarbon chains. These materials are not very soluble in water, and this procedure is more reliable for them than the simpler version used for low-molecular-weight quats. The analysis is performed as follows. It is virtually identical with ISO 2271 for anionics. 

Dissolve a sample containing 2-4 millimol of active in 20 ml propan-2-ol. 

Add 50 ml water and stir. Transfer quantitatively to a 11 volumetric flask, dilute to volume with water and mix. 

The titration is done the other way round for low-molecular-weight quats, i.e. those with only one alkyl chain, and whose molecular weights are 200-500. It is the exact converse of ISO 2271. 

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The methods described in this section and the next give a more or less complete analysis of the sample. The extractions in steps 1 and 2 can be done in the reverse order, in which case the first aqueous extract will contain the free ethanolamine plus the free fatty acid as soap, separation and determination of which is straightforward. The ester amine is determined by two-phase titration with sodium dodecyl sulphate. 

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