best source of usp lugol's?

I've been told that I need to get USP grade - I've been seeing some debates about the other classifications and it's a bit confusing. At least with USP grade I'm sure it's good for ingestion. I'm wondering who you guys find to have the most pure Lugol's iodine? I would appreciate links to the sites.

Also if you're recommending JCrow, the Lugol's on JCrow does not mention if it was USP or some other grade. Can anyone address that?

Thanks!!!!