Noncomplexing Tertiary Amines as "Better" Buffers Covering the Range of pH 3-11. Temperature Dependence of Their Acid Dissociation Constants.

Most of a broad series of buffers developed by Good (often called "Good's" or "Good" buffers) have been shown to cause metal ion interference as a result of complexation. A series of tertiary amines, devoid of hydroxy groups or other weak donors on the α, β, or γ carbons, have been developed as "Better" pH buffers which, as a result of steric hindrance, are incapable of forming even weak complexes with metal ions. As a result, they avert interferences of the type often encountered in metal ion studies which require buffer use. The compounds studied are alkyl and alkylsulfonate derivatives of morpholine (3), piperazine (3), ethylenediamine (3), and methylenediamine (1). With the exception of the morpholine derivatives, these compounds have two protonatable sites and, therefore, can be used to buffer two separate pH regions. A series of 10 buffer compounds span the entire range of pH 3-11. The acid dissociation constants for these compounds have now been determined in aqueous solution at 15, 25, 35 and 45 °C, μ = 0.10 M. From these data, apparent enthalpy and entropy values have been calculated to permit application at other temperatures as well. These buffers are recommended for use in all situations in which metal ions are present. All of the reported compounds are now commercially available.