Potentiometric titration of quaternary ammonium ion at the concentration level of 10-6 M with Ni(II)-dimercaptomaleonitrile complex
1977 Volume 26 Issue 4 Pages 272-274
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1977 Volume 26 Issue 4 Pages 272-274
On the equilibrium study of ion-pair extraction of anionic chelates with quaternary ammonium cations (Q+), a new method is earnestly desired by which trace amount of Q+ ion (10-6 M level) can be determined directly. Nickel(II)-dimercaptomaleonitrile complex [Ni(mnt)2]2- forms a stable ion-pair with Q+ ion and is quantitatively extracted into chloroform (Kex=[2Q+, Ni(mnt)22-]0/[Ni(mnt)22-][Q+]2=1023.85, where Q+ is (n-C6H13)4N+). Based on this fact, potentiometric titration of Q+ ion with Ni(mnt)22- was carried out with poly(vinyl chloride) membrane electrode, containing (7080)%(w/w) of di-2-etylhexyl-phthalate, as an indicater electrode for Q+ion. Cetylpyridinium chloride can be titrated at 10-5 M level, and tetra-n-hexylammonium chloride, tetradecyl-dimethylbenzylammonium chloride and tri-n-octylammonium chloride down to 10-6 M level.
In the case of mixture of several kinds of Q+ions, only a single end point was observed and corresponds to the total concentration of Q+ ions. This method was also successfully applied to the aqueous solutions containing (040)% ethanol, and to those satulated with chloroform.
