In analytical chromatography, the sample we analyze is usually rather dilute and allows the development of a rather straightforward method. Due to the minute concentrations we deal with in analytical chromatography, we face a linear behavior. The retention time of the analytes and the selectivity of a given separation can be forecast by simple rules that tremendously help us to develop efcient and fast separations. However, when we increase the sample size and a nite amount of sample is introduced in a chromatographic column, we leave the shelter of linear chromatography and have to cope with more complex peak shapes and phenomena.