purity                ≥98%
Cl                    ≤0.050%
NH4                 ≤0.020%
SO4                 ≤0.030%
Fe                   ≤30ppm
Pb                   ≤10ppm
As                    ≤1ppm
Other Amion Acids          negative

loss on drying                  ≤0.5%
ignition residue(H2SO4)     ≤0.10%
PH                        5.5～7.0