Overview
EN ISO 4098:2018 (IULTCS/IUC 6:2018) specifies a laboratory method for the determination of water-soluble matter, water-soluble inorganic matter and water-soluble organic matter in leather. The method is applicable to all leather types and is intended to produce comparable and reproducible results when test conditions are carefully reproduced.
The principle is straightforward: a prepared, dichloromethane-extracted leather sample is subjected to aqueous extraction under defined conditions. A measured aliquot of the filtrate is evaporated and dried to obtain the total water-soluble residue; sulfation and ignition (ash at about 700 °C) yield the water-soluble inorganic matter. The water-soluble organic matter is obtained by difference.
Key procedural elements from the standard include:
- Extraction of a ground, pre-treated sample with (500 ± 10) ml deionized water at (23.5 ± 3.5) °C.
- Mechanical shaking at (50 ± 10) cycles/min for (120 ± 10) min.
- Filtration and analysis of 50 ml aliquots of filtrate.
- Drying residues at (102 ± 2) °C and ashing at about 700 °C for inorganic fraction determination.
- Inclusion of ammonium salts in the water-soluble matter (they decompose on ignition; concentration may be determined separately if required).
Key Topics
- Sample preparation: grind and prepare samples in accordance with ISO 4044 and sample location per ISO 2418.
- Reagents and water quality: use deionized/distilled water complying with ISO 3696 (Grade 3) and 1 mol/l sulfuric acid for sulfating.
- Critical variables: degree of grinding, extraction temperature, extraction period and leather-to-water ratio - all must be controlled for comparable results.
- Apparatus: wide-neck flasks, shaking apparatus, evaporating basins, oven (102 ± 2 °C), muffle furnace (~700 °C), analytical balance (0.001 g).
Applications
This method supports practical applications such as:
- Quality control (QC) of incoming hides, processed leathers and finished goods.
- Process control and optimization in tanning and finishing operations.
- Supplier conformity checks and specification verification.
- R&D and formulation work to assess soluble additives or residues.
- Regulatory and environmental reporting where quantification of soluble organics/inorganics is required.
Related Standards
Relevant referenced standards (normative in EN ISO 4098:2018) include:
- ISO 2418 - sampling location for leather
- ISO 3696 - water for analytical laboratory use
- ISO 4048 - extraction with dichloromethane and free fatty acid content
- ISO 4044 - preparation of chemical test samples
- ISO 4684 - determination of moisture (dry substance basis)
Following EN ISO 4098:2018 ensures consistent, reproducible measurement of water-soluble fractions in leather, improving comparability across laboratories and supporting robust product quality and compliance programs.