Index Food grade Content ( Na2H2P2O7) % e 95.0 Phosphorus pentoxide P2O5 63.0-64.0 PH value 3.5— 4.5 Water-insoluble % d 1.0 Fluoride ( F) % d 0.005 Heavy metal ( Pb) % d 0.002 Arsenic ( As) % d 0.0003 Loss on burning 105 % d 0.5