Ttems	Norms (industrial grade)
	Superior-grade	First- grade	Qualified -grade
Na2SO3 -content % ≥	98.0	96.0	93.0
Fe-content % ≤	0.003	0.005	0.02
Water-insoluble matter content % ≤	0.02	0.03	0.05
Free alkali （ as Na）content % ≤	0.10	0.40	0.80
Na2SO4-content % ≤	2.5	——	——
NaCL-content % ≤	0.10	——	——