Orthophosphoric Acid is categorized primarily by its concentration and purity levels. Food Grade (85% purity) must meet FCC (Food Chemicals Codex) or E338 standards, ensuring heavy metal limits (like Arsenic < 3ppm) are strictly controlled. Industrial Grade (75%, 85%) is used for metal treatment and fertilizers, where slight impurities are permissible. For high-tech sectors, Electronic Grade (99.9%+) is required for semiconductor etching. Always request a Certificate of Analysis (COA) to verify the specific levels of iron, chloride, and sulfate.