Interesting that this topic has limped back to life relatively recently. My 2 currency-subunits' worth:

Several brands of white vinegar contain sodium sulphite, which would leave a residue on evaporation, probably sodium acetate. It's clearly just as valuable to do an evap test on your vinegar as your naphtha, it seems. For those so inclined and possessing the right equipment, redistilling the vinegar would be an option.

Why not go on a shopping trip to Germany? 25% acetic acid is sold in German supermarkets as "essig essenz" - vinegar essence. This probably doesn't need any sulphites...