Determination of weak (2.0–2.5) dissociation constants of non-UV absorbing solutes by capillary electrophoresis

Abstract

SummaryCapillary electrophoresis (CE) has proved to be a fast and convenient method for the determination of the dissociation constants of non-UV absorbing solutes in the acidic pK A range (2.0-2.5). The electroosmotic flow was reversed by washing the capillary with 0.2% polybren aqueous solution. A series of background electrolytes was prepared with phenylphosphonic acid (pK A = 1.29) and [3-alanine (pK A = 3.55) with the same ionic strength and a high buffer capacity in order to improve the repeatability (0.1-0.2 %) of the electrophoretic mobility and to determine the values of pK A accurately. This procedure was applied to the determination of the dissociation constants of several alkyl-alkylphosphonic acids whose pKA values have not yet been published in the literature. In this work, their dissociation constants have been found to vary between 1.91 and 2.34 for alkyl-methylphosphonic acids and between 2.10 and 2.38 for alkyl-ethylphosphonic acids.

Determination of pKa values by capillary zone electrophoresis with a dynamic coating procedure

“…3 A, 4 for all sulfonamides, an approximation of pK a could be carried out (Section 3.3). This process was an interesting alternative to the one extending the investigated pH range [21], as the latter leads to theoretical and practical drawbacks. For instance, a BGE of ionic strength superior to 20 mM is necessary for pH values inferior to 2.0.…”

Synthesis, resolution, and investigation of the rotational interconversion process of atropisomeric 1,n‐diaza[n]paracyclophanes using cyclodextrin‐mediated capillary zone electrophoresis

“…In an approximation the two pK a values were obtained as the minimum values of the first derivative of a function obtained from polynomial regression of the experimental data. 27 Pyridine and p-phenylenediamine (Merck) were used as reference.…”

Determination of dissociation constants of low molecular weight organic acids by capillary zone electrophoresis and indirect UV detection

“…However, this approach leads to increased ionic strength of the electrolyte, which can influence the migration of acidic analytes. To prevent this, several authors have used hexadimethrine bromide (polybren), first introduced by Terabe and co-workers [7,9,10]. The main advantage of using polybren is that it can be flushed through the capillary prior to adding the background electrolyte and thereby limiting the composition of the background electrolyte to that of the buffer system.…”