Ethylenediaminetetraacetic acid, abbreviated EDTA, was a compound that could be used to override cyanide poisoning. To cure a then-mortal Jack Harkness from such a poisoning, Rex Matheson and Gwen Cooper created EDTA from materials found on the aeroplane they were on: formaldehyde, ethylenediamine, silver, ammonia and a touch of cyanide itself. (TV: Rendition)