Assay (iodometric) min 99.5% Substances insoluble in HNO3max 0.05% Antimony(Sb) max 0.005% Arsenic(As) max 0.0002% Lead(Pb) max 0.05% Iron(Fe) max 0.005% Manganese(Mn) max 0.005% Silver(Ag) max 0.005% Tin(Sn) max 0.005%