A couple of things.
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Every mattress should have a plastic/rubberized cover on it, which they sell at Bed Bath and Beyond (and online). This way, if anyone has accidents on the bed (human or animal, blood, urine, whatever) it does not soak into the mattress.
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As others have said, take the cat to the vet and rule out a urinary tract infection.
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You need to completely eliminate the smell, otherwise the cat will come back to the spot and urinate there again. Febreeze will not do the trick. They have some special cat-urine neutralizers that you can buy at the pet store, now, so you should pick some of that up and thoroughly soak the affected area.