Industry Grade: Purity: 96.0%min Sulfur dioxide: 65.0%min Iron: 0.002%max Water insoluble: 0.05%max Ph value: 4.0-4.8 Food Grade: Purity: 98.0%min Sulfur dioxide: 65.0%min Arsenic: 0.0002%max Heavy metals(as Pb): 0.0005%max Selenium: 0.0005%max Iron: 0.001%max Water insoluble: 0.02%max Ph value: 4.0-4.8