This is going to be tricky because the discovery/synthesis of elements has taken place over centuries. It might be best to restrict this purely to the elements contained on Dmitri Mendeleyev's table, but I'd let the community decide. It may be too broad if all the elements are included, so this may be the best course of action.
Anyway, my question is fairly straightforward. When (and by who) were the elements on the periodic table (the modern-day one or simply Mendeleyev's) first standardized? I'd prefer that any answers not use Wikipedia.