Nah, you can detonate AN by itself, the oxygen from the nitrate part happily oxidizes the ammonium which will cause the nitrogen to depart the compound and rele

Nah, you can detonate AN by itself, the oxygen from the nitrate part happily oxidizes the ammonium which will cause the nitrogen to depart the compound and release a lot of energy and gas. The contaminants just enable the reaction to switch from burning through deflagration to detonation.