Determination of primary plus secondary amine

The ethoxylates of both mono- and diamines consist principally of tertiary amines, most of the primary nitrogen atoms adding on two ethylene oxide chains and the secondary nitrogen atoms of the diamines adding on one. Any surviving primary amine is the starting material, RNH2, and any secondary amine is either unreacted diamine or primary amine that has added on only one EO chain. Such chains are always short, mostly only one EO unit. The level of primary and secondary amines is low. 

This method [28] is a simpler version of the potentiometric method for primary and secondary amines given in section 7.2.2. The acid is added at step 4 to ensure the presence of an observable point of inflection. Observe appropriate precautions for carbon disulphide. 

Titrate potentiometrically with 0.1 M sodium hydroxide to just beyond the point of inflection. 

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Tertiary amines determination of primary plus secondary amines... 

In addition to the determination of total base, it is also possible to titrate mixtures. This can be done in two ways. One is to titrate mixtures based on the type of amines present. For example, one can distinguish between primary, secondary, and tertiary amines. This is done simply. Acetylate the primary and secondary amines in the mixture with acetic anhydride. They are converted to amides which are only weakly basic. Tertiary amines are not affected and titrate very well. A further differentiation can be made, however. The primary amine can be reacted with salicyl aldehyde to form a Schiff base. The secondary and tertiary amines are unaffected as far as basic strength is concerned, so that one can titrate the sum of secondary and tertiary amines. By these two titrations plus a determination of total amine, one can resolve the mixture. This approach works well for aliphatic amines, but not for aromatic amines. 

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