Item	90%	88%	85%	food grade
Na2S2 O4	≥ 90%	≥ 88%	≥ 85%	≥ 85%
(Fe)	≤ 20ppm	≤ 20ppm	≤ 20ppm	≤ 20ppm
(Zn)	≤ 1ppm	≤ 1ppm	≤ 1ppm	≤ 1ppm
Clarity	Clarify	Clarify	Clarify	Clarify
EDTA	-	-	-	Qualified
(As)	-	-	-	≤ 1ppm
Other heavy metals(pb)	-	-	-	≤ 1ppm
HCHO	-	-	-	≤ 0.05%
water insoluble matter	≤ 0.05%	≤ 0.05%	≤ 0.05%	-