Few things can survive 95% sulfuric, and give a fluorescence. This is quite a mystery you have on your hands. I would start with a complaint to a vendor, they may be able to help. I wouldn't be running HPLC on conc acid, but maybe ion chromatography systems and columns can handle it. Once isolated (if possible) the impurity can be understood better by other means.
I'd also check that this really is 95% sulfuric. If not, then that's a simpler complaint for the vendor. Also, I'd check if this impurity is stable towards heat, especially in 95% sulfuric.That would also let you know if its volatile enough for GC to be performed, once separated from the sulfuric acid.