They've been using them for a long time.
...Islamic State has used chemical weapons, including chlorine and sulfur, at least 52 times on the battlefield in Syria and Iraq, according to a study released in November by IHS Conflict Monitor, a London-based intelligence collection and analysis service.
The Organization for the Prohibition of Chemical Weapons said it had confirmed that Islamic State fighters had deployed sulfur mustard, commonly known as mustard gas, in an attack on the Syrian town of Marea, near Aleppo, in August 2015. The internationally banned substance burns a victim’s skin, throat and eyes.
“In this case, the team was able to confirm with utmost confidence that at least two people were exposed to sulfur mustard, and that it is very likely that the effects of this chemical weapon resulted in the death of an infant," the organization said in a statement....http://www.latimes.com/world/middleeast/la-fg-isis-chemical-weapons-2017-story.html