ISO 4048:2018

Overview

ISO 4048:2018 - Leather - Chemical tests - Determination of matter soluble in dichloromethane and free fatty acid content - specifies a standardized laboratory method to measure substances in leather that are soluble in dichloromethane and to determine the extracted free fatty acid content. Applicable to all leather types, the method defines sample preparation, two validated extraction techniques, drying and weighing procedures, and a titration-based determination of free fatty acids (expressed as oleic acid).

Key topics and technical requirements

• Scope: Quantifies extractable substances soluble in dichloromethane and the free fatty acids present in those extracts.
• Extraction techniques:
  • Soxhlet extraction (continuous extraction; minimum ~30 solvent changes).
  • Pressurized extraction system (high-temperature extraction; example procedure includes boiling at 180 °C for 40 min followed by percolation). Soxhlet is the reference method in disputes.
• Sample mass & preparation: Typical sample masses are 10 g (or 5 g when only soluble matter is determined). Samples are prepared according to ISO 4044 and sampled per ISO 2418. Duplicate analyses are recommended where possible.
• Solvent & safety: Primary solvent is dichloromethane (CH2Cl2); use analytical grade and follow supplier safety instructions (toxic properties). Solvent recovery by distillation is noted.
• Drying & weighing: Extracts are dried at (102 ± 2) °C for at least 6 hours, then cooled in a desiccator and weighed on a balance accurate to 0.1 mg.
• Free fatty acid determination: Extract is dissolved in a neutralized mixed solvent (diethyl ether/95% ethanol), then titrated with 0.1 mol/L NaOH using phenolphthalein (or alternative indicators for dark solutions). Results expressed as % oleic acid.
• Results reporting: Matter extractable expressed as percentage on dry matter (with volatile matter correction per ISO 4684). Reporting allows single-sample or mean of duplicates; values given to one decimal place.

Practical applications and users

ISO 4048:2018 is used by:

• Leather manufacturers and tanneries for quality control of finishing and fatliquoring processes.
• Textile and leather testing laboratories for conformity testing and material characterization.
• R&D and material scientists studying leather chemistry, additives, and degradation.
• Regulatory and procurement bodies requiring standardized composition data for sourcing and specification.

Practical benefits:

• Assesses residual fats, oils, plasticizers and other solvent-extractable substances that affect leather performance, feel and processing.
• Helps diagnose over- or under-fatliquoring, contamination (e.g., sulfur/impregnants), and informs corrective process control.

Related standards

• ISO 2418 - Sampling location for leather tests
• ISO 4044 - Preparation of chemical test samples (grinding)
• ISO 4684 - Determination of volatile matter
• ISO 4098 - Determination of water-soluble substances (used on residue after extraction)

Keywords: ISO 4048:2018, leather chemical tests, dichloromethane soluble matter, free fatty acid content, Soxhlet extraction, pressurized extraction, leather testing, extractable substances.