Nitro-9 was an explosive created by Ace in school, where she blew up the science building with it. Ace mixed it herself and put it inside deodorant cans.
Nitro-9 was a variant of Nitroglycerin. A variant of Nitro-9 was Nitro-9a, which was half the size and half as powerful. (NA: Timewyrm: Exodus) Another variant of Nitro-9 was Neo-Nitro, which resembled boiled sweets and was activated using saliva. (NA: Shadowmind) Ace also created Nitro-9 smart bombs, which could fly and take verbal commands. (NA: Blood Heat)
Though the Seventh Doctor told Ace not to carry it, she continued to do so and used it to destroy a Renegade Dalek (DW: Remembrance of the Daleks), a Cyber-shuttle (DW: Silver Nemesis) and to open the entrance to King Arthur's spaceship. (DW: Battlefield)
Ace also fired 1 can of Nitro-9 at Fifi that was chasing them through the pipes of the candy kitchen.The Happiness Patrol