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 testArsenic(As) max 0.0003%Magnesium(as alkali metals) max 1.0%Loss on drying(200oC, 4 hours) max 2.0%