Determination of total detergents surfactants

2 Photometric determination of anionic surfactants with methylene blue (MBAS). 

Most detergents (surfactants) are soluble in ethanol. The content of ethanol-soluble substances in the evaporation residue of a water sample therefore provides an indication of the scale on which these substances are present. It should be noted that other ethanol-soluble substances have a disturbing effect and that inorganic substances contained in the water may also pass into the ethanol extract. It is therefore advisable to re-extract the first extract with ethanol. 

Most detergents are substances which are sensitive to drying, so the drying time of the ethanol extract should be limited to 2 hours at 83 °C. 

Pleated filter Platinum or glass dish Drying cabinet Analytical balance Desiccator Method 

Add approximately 50 ml of hot ethanol to the evaporation residue of 1 or 2 litres water and use a glass rod to loosen and disperse any residues attached to the dish. After approximately 30 minutes on a boiling water bath, filter hot through a pleated filter into a glass dish. Then evaporate this first ethanol extract. Extract the residue once more with hot ethanol, and after filtration evaporate in a weighed dish (second extract). 

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