No, there are several alloys of copper that are made into wire. But
unless you have extremely special needs that are beyond the scope of
99.99% of jewelry requirements you will find no difference in the
alloys that are sold as copper wire. If you want to be sure you are
getting the same pure copper wire every time buy electrical wire as
impurities affect the conductivity of copper and electrical wire is
held to high purity tolerances.
James Binnion Metal Arts