Assay min 98.0% Substances insoluble in acetic acid max 0.2% Substances insoluble in HCl max 0.2% Chloride(Cl) max 0.025% Sulphate(SO4) max 0.25% Heavy metals(as Pb) max 0.002% Lead(Pb) max 0.001% Copper(Cu) max 0.001% Zinc(Zn) max 0.001% Iron(Fe) max 0.02% Barium(Ba) passes test Arsenic(As) max 0.0003% Magnesium(as alkali metals) max 1.0% Loss on drying(200oC, 4 hours) max 2.0%