Preparative Isoelectric Focusing

Isoelectric focusing using non-amphoteric buffers in free solution: II. Apparatus and measures of pH stability

Isoelectric focusing of amino acids or proteins requires a time-invariant pH gradient. The maintenance, in an electric field, of such profiles with simple non-amphoteric buffers is possible in multicompartment cells using well determined concentration profiles. The method for determining these concentration profiles has been proposed in a preceding paper. A multicompartment cell has been built for the purpose of verifying the assumptions made. The technical characteristics of this cell will be described here. The time-stability of pH profiles obtained with sodium acetate/acetic acid buffers has been measured for concentration profiles determined so as to keep constant the transport number of each ion throughout the cell. Measured over a time span of 10 h and with a current density of 96 mA cm-2, the pH shift is, in the worst case, 0.009 pH unit/h. This corresponds to a much better stability than the one obtained with a constant concentration of sodium acetate in all compartments, and justifies the chosen concentration profiles based on the condition of constant transport numbers. The above mentioned method for the computation of the buffer concentration assumed a constant relative mobility of the ions. The experiments have shown the limits of this assumption, i.e. the variation of ionic mobilities with the ionic strength and the temperature diminishes the stability of the pH gradient. However, slight adjustments of the concentration in the end compartments allow some improvement of the stability. If the temperature could be precisely controlled in each compartment, a better pH stability than what has been achieved in these experiments should be reached. Two methods of compensation of the migration of ions in the end compartments (buffer renewal method and external recycling method) have been tested and will be discussed.

New developments in isoelectric focusing

Recent developments of isoelectric focusing (IEF) are summarized. New approaches to the synthesis of carrier ampholytes are described and some controversial aspects of their properties, especially in regard to their molecular weight, are critically discussed. New aspects of preparative techniques, such as "steady-state rheoelectrolysis" and continuous-flow recycling IEF, are presented. New methodological trends of analytical IEF, such as agarose, cellulose acetate, ultrathin-layer and sub-zero temperature IEF are discussed. Among analytical applications, particular emphasis has been placed on detection of neutral mutations, IEF of peptides, IEF of cells and organelles and on titration curves. The review ends with a tiny chapter on a vast field, the explosive field of two-dimensional techniques.