Overview
ISO 5809:1982 specifies a standardized laboratory method for the determination of sulphated ash in starches and derived products. The procedure is based on controlled incineration of a test portion in the presence of sulphuric acid at 525 ± 25 °C. Results are reported as a percentage by mass, either as received or on a dry basis, and rounded to two decimal places. This method supports quality control, product specification and ingredient evaluation in starch processing and food industries.
Key topics and technical requirements
- Principle: Incineration of an accurately weighed test portion with sulphuric acid to convert volatile chlorides to non‑volatile sulphates and destroy organic matter.
- Temperature and equipment:
- Electric furnace with air circulation controlled at 525 ± 25 °C.
- Incineration dish (platinum or silica) capacity 100–200 ml, minimum useful surface 15 cm².
- Analytical balance, desiccator, hot plate/gas burner, water bath (60–70 °C).
- Reagents:
- Sulphuric acid solution: prepare by adding 100 ml concentrated H2SO4 to 300 ml water (handle carefully).
- Hydrochloric acid cleaning solution: 100 ml concentrated HCl to 500 ml water.
- Procedure highlights:
- Prepare and pre-calcinate the dish to constant mass (weigh to 0.0002 g).
- Weigh representative test portion (typical sample ≈ 5 g; special dilution procedures provided for bulky samples).
- Add 5 ml sulphuric acid solution to the sample, pre‑incinerate to carbonize, then incinerate in furnace until carbon residue disappears (typically ~2 h), cool, add drops of acid, re‑incinerate (~0.5 h) and weigh.
- Perform two determinations and report the arithmetic mean if repeatability criteria are satisfied.
- Performance criteria:
- Results expressed to two decimal places.
- Repeatability and reproducibility limits are specified (e.g., reproducibility: 0.1 g/100 g for ash < 0.5%; 20% of mean for ash between 0.5–5%; 1% of mean for ash > 5%; repeatability limits also defined).
Applications and who uses it
- Quality control laboratories in starch production and starch‑derived product manufacturing.
- Food ingredient suppliers and formulators verifying mineral/ash content.
- Regulatory bodies and certification labs validating product compliance and label claims.
- Research and development groups studying composition, processing effects or formulations involving starches and syrups.
- Uses include specification compliance, contamination monitoring (e.g., mineral residues), product grading and formulation optimization.
Related standards
- ISO 1666 - Determination of moisture/loss on drying (relevant for dry‑basis reporting)
- ISO 1741, ISO 1742, ISO 1743 - Determination of dry matter for glucose/dextrose/glucose syrups
Keywords: ISO 5809, ISO 5809:1982, sulphated ash, starches and derived products, incineration method, ash content, analytical method, dry basis.
