Index name	Premium grade	First grade	Second grade
Assay%	≥99.0	≥98.5	≥98.0
sodium nitrate%	<0.80	<1.00	<1.90
Chloride%	≤0.10	≤0.17	-
Moisture%	≤1.8	≤2.0	≤2.5
Water insoluble matter%	≤0.05	≤0.06	≤0.1