How can I effectively clean old cat urine from a mattress?

To effectively clean old cat urine from a mattress, start by blotting up as much urine as possible with paper towels. Then, mix equal parts water and white vinegar in a spray bottle and spray the affected area. Let it sit for 10-15 minutes before blotting it up with more paper towels. Finally, sprinkle baking soda over the area, let it sit for a few hours, then vacuum it up. Repeat these steps as needed until the odor is gone.