It is shown that by using only a series of tubes with constant cross-sectional area and a single-channel peristaltic pump, it is possible to produce solute gradients with time profiles that are concave, convex, sigmoid or even with turning points. The general theory for predicting gradients, by using tubes in series that are either open or closed to the atmosphere, is presented, and the equations using three compartments are given. Experiments are described that support the usefulness and accuracy of such a theoretical treatment.
