How can I effectively remove the old cat urine smell from a mattress?

To effectively remove old cat urine smell from a mattress, start by blotting the area with paper towels to absorb as much liquid as possible. Then, mix equal parts water and white vinegar in a spray bottle and saturate the affected area. Let it sit for 30 minutes before blotting it dry. Sprinkle baking soda over the area and let it sit for several hours or overnight to absorb any remaining odor. Vacuum the baking soda off the mattress and repeat the process if necessary.