Ouch - how is this made? Not that i'm interested in it, but, - since you asked...
It's made by adding PF
5 to the mixture of anh. HNO3/HF and filtering the pptated salt
Sounds like fun, doesn't it?
HF can bee formed in situ from the same pentafluoride, yield in this case sucks, though - see
Patent US3092459
Other perfluoro Lewis acids may bee used as well, see
Patent US3403987
Antoncho