Yes, they can 'prove' what is in something to the limits of the physics.
However, the human in the loop is quite frail for most operators. In that, these very fancy and very expensive instruments are mostly run by high school grads and serviced by field engineers with a huge backlog.
For a first time one off test of something's composition, I'd go for at least 3 companies and preferably you have a history with them. This stuff is terribly complicated and misinterpretation is shockingly common. If the tech hasn't used the standards before then your at the mercy of fate.
Like, we have 5 (!) places on the home screen that do the exact same function of ending a run because when we try to consolidate it to just 1, our customers freak out and can't find where the button went to. Granted they pay $100k+ per instrument plus service plan, so we add it back in no question ( and this is life critical equipment in many cases), but I hope that shows how embedded to routine these operators get.