The elevation in boiling point of a solution is given by $\Delta T_b = K_b m$. The molal elevation constant $K_b$ for a solvent depends on:

$K_b = \dfrac{M_A R (T_b^\circ)^2}{\Delta H_v}$, where $M_A$, $T_b^\circ$ and $\Delta H_v$ are properties of the pure solvent. $K_b$ therefore depends only on the solvent, not on the identity or amount of solute, which is exactly why $\Delta T_b$ is a colligative property.