"Is nitrogen gas the best modern execution alternative to lethal injection?"

As I note in comments, curious how this new "solution" is never used. Is it the connotation of "gas" in general? Or, as suggested, its connection to euthanasia? Problem with "unusual" punishments? Something else? Also, "best" doesn't mean the punishment is substantively acceptable. But, if it exists, the best possible means should be used. What is the goal there?