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

Abstract

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.

The effect of conditioning of fused‐silica capillaries on their electrophoretic performance

“…We used a series of alkyl and alkylsulfonate derivatives of morpholine, piperazine, ethylendiamine, and methylenediamine that are thought to be sterically hindered and hence incapable of chelating metal ions [22]. These noncomplexing zwitterions (commonly known as "biological", "Good's", "Good", or even "better" buffers) should exhibit minimum interference with any trace metal impurity that may be present at the silica surface.…”

“…BGE working solutions were prepared by diluting appropriate amounts of 0.250 M buffer, 2.00 M NaOH (or 2.00 M HCl), and 2.00 M NaCl stock solutions to obtain the same 25.0 mM buffer concentration and the same 50.0 mM ionic strength. Calculations were done by using the program Bufcalc [23] and the pK a data reported by Kandegedara et al [22].…”

Algal Toxicity Tests for Environmental Risk Assessments of Metals

“…From the foregoing, it also is apparent that an increase in pH (>±1) during the test period should be avoided when evaluating metal toxicity. To obtain a constant pH, several methods could be applied such as frequent adjustments of the pH with a nontoxic acid, through the use of a noncomplexing and nontoxic buffer such as MOPS (De Schamphelaere et al, (personal communication); Kandegedara and Rorabacher 1999;USEPA 1991) or by using airtight test flasks with CO 2 -enriched headspace (Halling-Sorensen et al 1996). Although pH can be controlled with these techniques, one still might question the ecological relevance of CO 2 -limited test conditions.…”

Comparison of the capacity of two biotic ligand models to predict chronic copper toxicity to two Daphnia magna clones and formulation of a generalized bioavailability model

“…Tests were conducted at pH 6.5 and pH 8.3. Test solutions were adjusted to the required pH of 6.5 by adding 3-N-morpholinopropanesulfonic acid (MOPS) and the required amount of NaOH or HCl; MOPS is not toxic and affects neither metal speciation [19] nor copper toxicity to freshwater organisms [20]. Because the buffering capacity of MOPS is restricted to a pH range of 6.5 to 7.9 (acid disassociation constant ¼ 7.2), test solutions for pH 8.3 were adjusted to the required pH by adding NaHCO 3 (3 mmol/L) and the required amount of NaOH or HCl.…”