The formation of stable pH gradients with weak monovalent buffers for isoelectric focusing in free solution

Instabilities of the pH gradient in carrier ampholyte-based isoelectric focusing: Elucidation of the contributing electrokinetic processes by computer simulation

Electrokinetic processes that lead to pH gradient instabilities in carrier ampholyte-based IEF are reviewed. In addition to electroosmosis, there are four of electrophoretic nature, namely (i) the stabilizing phase with the plateau phenomenon, (ii) the gradual isotachophoretic loss of carrier ampholytes at the two column ends in presence of electrode solutions, (iii) the inequality of the mobilities of positively and negatively charged species of ampholytes, and (iv) the continuous penetration of carbonate from the catholyte into the focusing column. The impact of these factors to cathodic and anodic drifts was analyzed by simulation of carrier ampholyte-based focusing in closed and open columns. Focusing under realistic conditions within a 5 cm long capillary in which three amphoteric low molecular mass dyes were focused in a pH 3-10 gradient formed by 140 carrier ampholytes was investigated. In open columns, electroosmosis displaces the entire gradient toward the cathode or anode whereas the electrophoretic processes act bidirectionally with a transition around pH 4 (drifts for pI > 4 and pI < 4 typically toward the cathode and anode, respectively). The data illustrate that focused zones of carrier ampholytes have an electrophoretic flux and that dynamic simulation can be effectively used to assess the magnitude of each of the electrokinetic destabilizing factors and the resulting drift for a combination of these effects. Predicted drifts of focused marker dyes are compared to those observed experimentally in a setup with coated capillary and whole column optical imaging.

On the use of dimensionless parameters in acid-base theory. IV. The pH of water solutions of acids, bases, and simple ampholytes

Exact relations between pH and concentrations of water solutions of acids, bases, and simple ampholytes are presented in the form of computer-created curves. These are mathematically analysed with respect to linearity and inflexion points. The extreme invariance of pH in the immediate vicinity of the isoelectric points of ampholytes is demonstrated in curves of the logarithm of molarity as a function of the logarithm of magnitude of pH-pI magnitude of. These considerations include a discussion of the suitability of ampholytes as pH standards.

Nonamphoteric isoelectric focusing: II. Stability of borate-glycerol pH gradients in recycling isoelectric focusing

By complexing polyols with borate in recycling isoelectric focusing and by varying the ratio of polyol to borate over the useful pH range of 4.0-6.0, it is possible to control pH. Twelve solutions of 0.1 M boric acid and varying glycerol concentration were used to vary pH in a twelve-compartment commercial recycling isoelectric focusing (RIEF) system. Various concentrations of boric acid were tested as anolyte, and various Tris(hydroxymethylamino)methane-borate buffer systems were tested as catholyte. Electroosmosis, hydrogen ion flow, and fluid balancing were characterized in two glycerol gradients; one was maintained at 0.06 pH/fraction and the other at 0.12 pH/fraction. In the latter case, ovalbumin (pI4.70) migrated to the pH 4.61 and 4.72 compartments. It is concluded that the borate-glycerol system can be adequately stabilized in RIEF for isoelectric purification of certain proteins.

Steady state electrolysis and isoelectric focusing

The properties of pH gradients formed by stationary electrolysis of weak mobile or fixed electrolytes are analyzed. The model uses the appropriate balance equations and those of chemical equilibria. It is shown how the equation of the current density has to be modified for considering that fraction of current that is associated with the diffusion of neutral buffer molecules within a pH gradient. Furthermore it is shown that the pH gradients themselves give rise to water production within the gradient and that essential properties of the steady state are related to chemical reactions between the electrolyte constituents. The differential equations describing the gradients of the concentration of a given component, the pH, conductivity and potential are explicitly formulated in relation to those reactions. The equations are solved numerically and the significance of the results for isoelectric focusing is discussed. The experimental conditions to reach shallow and smooth pH gradients exhibiting sufficient ionic strength are formulated.