Ammonium Chloride sublimes when heated whereas Barium Sulfate does not. Another method would be to add de-ionized water to the mixture. The solids left over will be the Barium Sulfate whereas the the Ammonium Chloride will be mixed with the de-ionized water. Weigh everything first, including the water because the Ammonium Chloride will sublime when dry if you try to evaporate the de-ionized water from the mixture.