I don't think there's enough dextrose in salt to amount to anything unless you have an extremely severe allergy, not just a sensitivity.
Have you checked yourself to find out your tolerance? I have. I tolerate 2000 mcg a day of sulfite.
There is a formula and directions to figuring out your tolerance in Rick Williams' free ebook www.learningtarget.com/nosulfites/
Don't get uptight about
a little sulfite here and there. Calculate how much is in the food you eat every day. If you don't get a reaction you are under your limit. This isn't a peanut allergy!