Step 10 corresponds to template application and impurity prediction. As template species are carrier fragments, they can be aligned with respective query species, causing the desired transformation into impurities based on the atom mapping. In Figure , the aromatic hydroxyl carrier fragment corresponds to either query species 3 (i) or 1 (ii), whilst the anhydride fragment corresponds to Applying the template to respective query species leads to impurity and 4-aminophenyl acetate as well as acetic acid in both cases. Therefore, each analogue reaction can lead to one or more impurity reactions via a template depending on carrier fragments in the template and combinations of possible query species containing these carrier fragments.