2. From analytical to preparative: the problem of scaling up

The definition of preparative electrophoresis and its boundary with the analytical field are very tricky to establish. Experiments that a few decades ago were regarded as analytical can now sometimes be described as "preparative", since the separated products are recovered for use in subsequent operations. Enormous progress has made detection increasingly sensitive and recovery increasingly efficient, enabling quantitative assays. For example, very small quantities (on the order of micrograms) are sufficient to determine the sequence of a protein. Crystallization of proteins or substances also requires only a few milligrams. Finally, tests more specifically related to biological activity can be carried out with product quantities of less than a gram. For all these applications, electrophoresis is an excellent purification tool. However, the transition from analysis to preparation, whatever...