The protonation state of functional groups in a molecule can significantly impact its chemical properties and reactivity. Pre-canonicalization steps include adjusting the protonation and deprotonation states of functional groups to reflect the most probable physiological conditions or experimental settings. This ensures that the resulting InChI provides a relevant representation of the molecular structure under consideration. Recognising and representing the ways that this can interact with elements that can exhibit variable oxidation states is particularly important in inorganic systems.