Amphoteric substances defined

Salts, which are the products of acid-base reactions, are thus not necessarily electrically neutral but rather exhibit well-defined acid-base properties in water. Acidity appears as a relative concept and the existence of amphoteric substances, i.e. substances which can behave either as acids or bases depending on the circumstances, is stressed. The proton concentration, [H+], quantifies the acidity of a solution and the pH scale is established ... 

The modified approach has been used by ourselves in conjunction with IGC studies of various polymers. Although the determination of AN is somewhat cumbersome, the ability to define acid/base parameters in thermodynamically consistent units enhances the utility of the Gutmann model It allows recognition of the fact that most macromolecules are amphoteric in character that acid/base interaction potentials may be strongly T-dependent that the balance of acid/base forces in any given substance may be represented by a unitless ratio number, such as AN /DN. We expect considerable expansion in the near future of the available AN, DN data base. 

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