ISOELECTRIC-FOCUSING IN NON-AMPHOTERIC BUFFERS - CATASTROPHE AND NON-CATASTROPHE THEORIES

Four potential modes of isoelectric focusing in non-amphoteric buffers are evaluated:(a)"stack" or "train" of free bases or acids "arrested by a deprotonation or protonation mechanism", respectively (Chrambach); (b) "chemically bonded" (immobilized) pH gradients (Righetti et al.); (c) "physically bonded" or "quasi-immobilized" pH gradients (Bier et al.); (d) steady-state rheoelectrolysis (Rilbe). The first is based on a "catastrophe" theory, i.e., it confines the buffers in a pH region where they can create a pH gradient by an isotachophoretic mechanism, but where they do not have sufficient buffering capacity to stabilize it; no true isoelectric focusing can ever be achieved with this system. The last three are based on sound and well defined theories; however, at present, only system (b) (immobilized pH gradients) has proved to be a simple and reliable technique, easily transplantable in any laboratory. Bier et al.'s and Rilbe's approaches require complex and elaborate experimental set-ups and strict adherence of laboratory practice to a set of physical laws governing the system. In practice, owing to the divergence of experimental approaches from idealized physical equilibria, the last two approaches appear still to be far away from daily laboratory work.