IS CHROMATOGRAPHY A SEPARATION PROCESS - THE ZONOID ANSWER

The separation state of a physical system is defined as a geometric entity called a zonoid and a brief account of the mathematical properties of zonoids is given. Visual representations of (2-D and 3-D) zonoids enhance the intuitive grasp of the theory and calculation of their volume gives a useful (although degraded) measure of separation. The answer to the title question is then, on rigorous grounds, that chromatography is not a separation, but a "sepmix" process, i.e., it is both a separation and a mixing process. In linear chromatography, loss in 2-volume of separation between a solute and carrier increases along the column approximately according to square-root N, where N is the number of theoretical plates. 3-Volume of separation between two solutes and carrier first increases and then decreases. More intricate topics such as selectivity of separation are defined and discussed. Examples of problem solving with zonoids are given and it is shown that Rony's extent of separation results from a problem of approximation and reflects only part of separation produced by the column.