how about:
there might be organic impurities in the salt, where the organic impurities will form volatile chloride with conc HCl instead of forming metal chloride?
Organic halides do have low boiling points and hence the volatility at room temperature, but they will be formed only if a reaction between HCl and he organic impurity is possible.
quote from AWK :
Metals chlorides are most volatile salts. HCl does not reacts with Pt.
quote from AWK:
Some impurities are soluble in concentrated HCl used for washing; others are converted into chlorides on the surface of wire - chlorides are the most volatile salts among common salts; then are removed from wire by heating.
I too would prefer to think of inorganic impurities on a Pt wire than organic ones. Please feel free to correct me if I am wrong.