... Alkaline 0.4max 1.Re: sodium sulphite anhydrous -Appearance: White powder. Certificate: SGS, BV,CIQ-Specification: Content 97% min Iron 0.005% max ... 29672000Sepcification: Index name Premium grade Super grade First grade Sodium sulfite ( Na2SO3 ) , % ≥97.0 96.0 Fe , ≤0.003 0.005 ... matter , % ≤0.02 0.03 Free alkali ( as Na2SO3 ) , % ≤0.10 0.40 Na2SO4 , % ≤2.50 / NaCl , % ≤0.10 / sodium sulphite