Overview
ISO 3627:2001 - "Photography - Processing chemicals - Specifications for anhydrous sodium metabisulfite" defines purity and test requirements for photographic‑grade anhydrous sodium metabisulfite. The standard establishes chemical and physical acceptance criteria, prescribes test methods (including titration procedures), and references general analytical methods for sampling and safety. It is intended to ensure chemicals used in photographic processing do not cause undesirable photographic effects.
Key topics and requirements
- Scope: Criteria for purity and tests to determine suitability for photographic use.
- Physical & storage: White or pale‑cream granular powder; store in a closed container at room temperature; avoid contact with acids.
- Mandatory requirements (summary):
- Assay (Na2S2O5): minimum 95.0% by mass.
- Mass fraction of heavy metals (as Pb): maximum 0.005%.
- Mass fraction of iron (Fe): maximum 0.005%.
- Mass fraction of thiosulfate (as S2O3 2−): maximum 0.03%.
- pH value (aqueous solution): 3.7 to 4.6.
- Reaction to ammoniacal silver nitrate: to pass test (identity/specific reactivity).
- Appearance of solution: clear and free from insoluble matter except for slight flocculence.
- Test methods: The standard specifies reagents, sampling, apparatus and analytical procedures, including back‑titration and direct‑titration assay methods using iodine/thiosulfate systems. It cites ISO 10349 series methods for general procedures, heavy metals/iron determination, and ammoniacal silver nitrate reaction tests.
- Safety note: Procedures may involve caustic or toxic reagents; ISO 3627:2001 highlights safe laboratory practice and references ISO 10349‑1 for hazard symbols and handling.
Applications - who uses this standard
- Photographic chemical manufacturers and raw material suppliers for quality control and product specifications.
- Analytical and quality‑assurance laboratories performing routine purity testing of anhydrous sodium metabisulfite.
- Photographic processors, conservation labs and formulators who require assurance that processing chemicals meet photographic‑grade purity to avoid defects.
- Procurement and compliance teams specifying supplier conformance for photographic processing chemicals.
Related standards
Keywords: ISO 3627:2001, anhydrous sodium metabisulfite, photographic‑grade, processing chemicals, purity assay, heavy metals, thiosulfate, pH, test methods.