I'm working on a new invention that requires a disposable instant ice pack using ammonium nitrate and water. I need the temperature of this new ice pack to get within the range of -15 deg F I have tried using larger quantities of ammonium nitrate but was only able to lower the temperature 6-8 degrees colder...nothing significant. Current disposable ice pack reach 30-40 deg F and are required by the EPA to maintain this temp for 20 minutes to qualify as an ice pack. Mine would only need to stay cold for a 2-3 minutes. I've read that most instant ice packs typically use less than 28% nitrogen in its formulation. Maybe increasing the nitrogen content would work?