What factor can limit the buffering capacity of a molecule?

The concentration and pKa of an acid and its conjugate base can limit the buffering capacity of a molecule.

Explanation:

A buffer is an acid and its conjugate base and the quality of it depends on its buffer capacity. This buffer capacity is the resistance to change the pH of the solution when strong acids or bases are added. The buffer capacity is related to the buffer concentration, the concentration of the acid end its conjugate base. Also, every acid has a pKa and the buffer capacity is at its maximum at the pKa value and can buffer the solution between ± 1 the pKa value.