Assay (acidimetric on dried min 98.5%substances)pH(5% solution 20oC) 4.5-6.0Chloride(Cl) max 0.002%Nitrate(NO3) max 0.002%Heavy metals(as Pb) max 0.001%Iron(Fe) max 0.001%Arsenic(As) max 0.0005%Loss on drying(105oC) max 1.0 %Residue on ignition (as SO4) 0.05%