Correct classification and identification of autocatalysis

It is generally accepted that autocatalysis is a kinetic phenomenon, where a product of a reacting system functions as a catalyst. Consequently, the reaction proceeds faster upon adding the corresponding product to the unreacted mixture of reactants providing an unequivocal possibility of how a system may be identified either experimentally or theoretically as an autocatalysis. Once this is approved, it often results in sigmoidal concentration-time profiles, though it is neither a necessary nor sufficient prerequisite because appropriate mechanistic and parametric conditions must be met to give rise to the appearance of this kinetic feature. Several mass action type kinetic models producing sigmoidal concentration-time profiles are systematically analyzed to clarify their correct characterization and classification. This procedure has led us to refine the definitions of autocatalysis and autocatalyst. A kinetic phenomenon where a product of the overall chemical event serves as a catalyst for at least one of its subsystems or for the whole system itself is called autocatalysis. This definition makes it clear that in the case of autocatalysis, the concentration of autocatalyst necessarily increases during the course of any real overall chemical or biochemical reaction. The way it is achieved thereby provides a suitable tool to classify autocatalytic processes by their elucidated and fine mechanistic details.