פירוש על קידושין 82:1

The mishnah allows one to appoint an agent to give terumah on his behalf. How do we know that such an act is valid and that such produce is actually considered terumah?

We cannot derive agency for terumah from agency from divorce because terumah is considered holy, whereas divorce is not an issue of holiness. Since these are different fields, we cannot derive one from the other.

The word “also” is read as including an agent in separating tithes and terumah.