1) Content (as stable Vc) ≥ 35% 2) Loss on drying ≤ 6.0% 3) Ph 6.0 ~ 9.5 4) Heavy metals (as Pb) ≤ 30 ppm 5) Arsenic (as As) ≤ 10 ppm 6) Particle size 60 ~ 100 mesh Inner packing: plastic liner Outer packing: 25kg/multiple paper bag