K2S2O5 M.W. 222.31Assay(iodometric) min 95.0-99.9%Iodometric, SO2 54.8-57.6%Appearance of solution pases testpH (5% in water) 3.0-4.5Chloride(Cl) max 0.05%Heavy metals (as Pb) max 0.001%Thiosulphate passes testCopper(Cu) max 0.0025%Zinc(Zn) max 0.0025%Iron(Fe) max 0.002%Selenium(Se) max 0.0005%Arsenic(As) max 0.0002%Mercury (Hg) max 0.0001%