Well not in terms of pH, but there are several acids that can exist as a pure liquid, undiluted by water. Pure vinegar, undiluted by water, is called glacial acetic acid. It is something that can be bought from a chemical company. Because there is no water, there isn't really a pH. That doesn't mean it isn't incredibly hazardous, though.

>Because there is no water, there isn't really a pH.

Could you elaborate? Wikipedia doesn't seem to suggest water is necessary (it talks about moles per unit volume) but I may be misunderstanding something.

The definition of pH is pretty much a measure of the proton concentration of things dissolved in water. You can look at similar measures in non aqueous solution but then it doesn't fit the definition properly.

I'd say you have moles per unit volume of H3O+ ions. These form as the combination of H+ ions (readily present in copious amounts of acid) and crucially, H2O molecules.

On the other hand, pure oleic acid isn't especially toxic. It's a major component of Lorenzos oil.

Nuthin but protons?