Determination by the cobaltothiocyanate colorimetric method

The method can be used for raw materials and for products containing anionic surfactants, but not cationics or amphoterics. It is also valid for polypropoxylates. 

Colour reagent. Dissolve 30 g cobalt (II) nitrate, Co(N03)2.6H2O, 143 g ammonium chloride and 256 g potassium thiocyanate in water, dilute to 11 and mix. Alternatively dissolve 30 g cobalt (II) nitrate, 200 g potassium chloride and 200 g ammonium thiocyanate in water, dilute to 11 and mix. 

Dissolve 1.000 g of pure nonionic surfactant of the type to be determined in water, ensuring complete dissolution, transfer to a 250 ml volumetric flask, dilute to volume and mix. 

Titrate 50 ml of this solution to methyl red with 0.1 M hydrochloric acid. Note the volume used and discard the solution. 

Place a second 50 ml portion in a 100 ml stoppered cylinder, add the volume of acid used by the first portion, dilute to 100 ml and mix. This solution contains 2.000 mg/ml of the nonionic. 

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