Would it be ok to do this before putting new plants in the tank to prevent parasites and other diseases getting into the tank or would this just kill the plant?
Seriously though, yes it would kill the plants. Try dipping them for several minutes in a solution of Malachite & Formalin (5ml of each in a gallon of water). This is often used in the trade as a net dip. No doubt other members will be able to suugest other methods as well B)