When purchasing Selenium Solution, the most critical factor is the chemical concentration (purity level), typically ranging from 99.9% to 99.99% for high-end applications. You must verify the CAS Number (e.g., 7782-49-2 for elemental selenium) to ensure chemical identity. For liquid forms, specify the solvent type (e.g., nitric acid or water-based) and the molarity/concentration (ppm). Additionally, check for trace metal impurities, as even parts-per-billion (ppb) levels of contaminants like copper or iron can affect performance in glass manufacturing, electronics, or solar cell production.