Overview
ISO 4047:1977 defines a standardized laboratory procedure for determining sulphated total ash and sulphated water-insoluble ash in leather. The method is applicable to all types of leather and is intended to support complete leather analysis by quantifying mineral matter after carbonization, sulphating and controlled ashing. Key practical benefits include consistent ash-content measurement for quality control, formulation checks and regulatory/compliance documentation.
Key Topics
- Scope: Method covers determination of sulphated total ash and sulphated water-insoluble ash for all leather types. Ammonium salts are not determined by this method.
- Principle: Carbonize leather sample, treat the resulting ash with sulphuric acid, then ignite in an open crucible at a controlled temperature (close to, but not exceeding, 800 °C) to obtain the sulphated ash.
- Reagents & materials: Use analytical-grade reagents only. Typical reagents cited in the standard include ~2 N sulphuric acid and an ammonium nitrate solution (~100 g/L). Only distilled or equivalent purity water should be used.
- Apparatus: Ordinary laboratory equipment plus glazed porcelain, platinum or quartz crucibles and a muffle furnace capable of maintaining about 800 °C.
- Procedure notes:
- For sulphated total ash: weigh 2–5 g sample, carefully carbonize, moisten with sulphuric acid until SO3 fumes cease, then ash at 800 °C until constant mass is obtained.
- For sulphated water-insoluble ash: first extract water-soluble substances per ISO 4098, air-dry residual leather, then proceed as for total ash.
- If carbon-free residue is difficult to obtain, a small amount of ammonium nitrate may be used and heating repeated.
- Accuracy & repeatability: Duplicate determinations by the same operator should not differ by more than 0.1% (based on original sample mass).
- Limitations: Organometallic compounds and volatile salts may affect results; avoid furnace temperatures above 800 °C to prevent volatilization losses. Leather impregnated with volatile organo-metallics can be pre-extracted (e.g., dichloromethane) if required.
Applications
- Quality control and batch verification in tanneries
- Material composition and formulation analysis
- Regulatory compliance documentation and reporting of inorganic content
- Support for further component analysis (e.g., oxide determinations from retained ash)
Related Standards
- ISO 4098: Determination of water-soluble matter and water-soluble inorganic matter in leather (referenced for pre-extraction when determining water-insoluble ash)
- ISO 4044: Preparation of chemical test samples
- ISO 2418 and ISO 2588: Sampling and sample identification guidance
This standardized method provides repeatable, documented determination of mineral residue in leather and integrates with broader leather-testing workflows for reliable, auditable results.
