| Property | Specification | Test Method | Units |
|---|---|---|---|
| Appearance | White crystals or crystalline powder | Visual | – |
| Assay (as Na₂S₂O₄) | Min 99.0% | Titrimetry | wt% |
| Sodium Sulfite (Na₂SO₃ | Max 1.0% | Titrimetry or Gravimetry | wt% |
| Water Insoluble Matter | Max 0.1% | Gravimetry | wt% |
| pH (of a 10% solution) | 6.0 – 8.5 | Potentiometry | – |
| Iron (as Fe) | Max 50 ppm | Atomic Absorption Spectroscopy (AAS) | ppm |
| Copper (as Cu) | Max 20 ppm | Atomic Absorption Spectroscopy (AAS) | ppm |
| Calcium (as Ca) | Max 0.1% | Gravimetry or Inductively Coupled Plasma (ICP) | wt% or ppm |
| Loss on Drying | Max 0.5% | Gravimetry | wt% |
| Chlorides (as Cl) | Max 100 ppm | Ion Chromatography | ppm |
| Sulfates (as SO₄) | May not be tested (since it’s a component of sodium hyposulfite) | – | – |
