Content of not less than 98.0% The maximum impurity content (indicator in%) Clarity test pass Dilute hydrochloric acid insoluble matter 0.005 Sulfate (SO4) 0.01 Nitrate (NO3) 0.003 Ammonium salt (NH4) 0.005 Lead (Pb) 0.002 Iron (Fe) 0.0005 Basic salt (ZnO) 1.2 Ammonium sulfide does not precipitate (sulfate) 0.1