Tensio-active substances

In order to control this disadvantageous effect, de-foamers and de-aeraters are added19. The defoamer s task is to control the foam formation due to the tensio-active substances, while the de-aerater removes gas bubbles, in solution and in the fibre structure. In this way, the contact surface between fabric and bleaching solution is kept maximal, which can only favour the rate of the process. By adding the de-aerater, lower quantities of tensio-active substances are needed, which helps to minimise foam formation. 

Sometimes other variables must be investigated such as the pH and/or the ionic strength of the buffer in the mobile phase or the concentration of additives in the mobile phase such as for instance tensio-active substances in micellar chromatography. In such a case the first step in an optimization is to screen these factors and to identify the most important ones for the subsequent optimization. The screening (Section 6.4.2) leads to a definition of the experimental domain in which the optimum is probably situated. This is somewhat similar to the retention optimization step. It is followed by an optimization step (Sections 6.4 and 6.7), in which the most important variables are changed, often according to an experimental design. Similar methods are used in capillary zone electrophoresis. 

Determination of hydrophilic-lipophilic balances of some surfactants using tensio-active compoimds as stationary phases and injection of substances of suitable structure (normal hydrocarbons and alcohols) has also been recorded [126—127]. 

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