Overview
EN ISO 23649:2025 - Chemicals for the leather tanning industry: Determination of cyclosiloxanes (ISO 23649:2025) specifies a standardized analytical method for measuring the total content of three cyclosiloxanes - octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) - in chemicals used in leather tanning (for example, silicone-based waterproofing fatliquors and finishing agents). The method uses gas chromatography with a single quadrupole mass spectrometer (GC‑MS) following sample solubilisation and liquid–liquid extraction.
Key topics and requirements
- Analytes: D4, D5, D6 (cyclosiloxanes) - all noted in the document as classified in the EU as persistent, bioaccumulative and toxic (PBT).
- Analytical technique: Gas chromatography (GC) coupled with a single quadrupole mass spectrometer (MS) for identification and quantification.
- Sample preparation:
- Solubilise the chemical specimen in water (water grade 1, ISO 3696).
- Perform liquid–liquid extraction using an n‑hexane : ethyl acetate (50:50 v/v) mixture.
- Use internal standardisation to compensate for matrix effects and recovery.
- Annex C covers sample preparation for non‑water‑soluble chemicals.
- Calibration and quantification:
- External calibration with correction for the internal standard recovery.
- Stock solutions and internal standards (examples: Naphthalene‑D8 or Tetrakis(trimethylsilyloxy)silane) are specified.
- Apparatus and reagents: Ultrasonic bath, shaker, centrifuge, syringe membrane filters (e.g., 0.2 µm), GC vials, analytical balance, n‑hexane, ethyl acetate, sodium chloride, anhydrous MgSO4, and certified reference cyclosiloxanes.
- Supporting information:
- Annex A: recommended chromatographic operating parameters for GC‑MS.
- Annex B: method precision / reliability data.
- Annex C: normative sample prep for non‑water‑soluble matrices.
Applications and users
This standard is intended for:
- Laboratory analysts and quality control teams in tanneries and leather chemical manufacturers monitoring silicone additives.
- Third‑party testing laboratories performing compliance testing for product safety and environmental reporting.
- Regulatory and environmental monitoring bodies tracking PBT substances in leather industry chemicals.
- Suppliers and formulators who need to verify cyclosiloxane content in waterproofing fatliquors and finishing agents.
Practical benefits include reproducible test results across labs, support for regulatory compliance, supply‑chain verification, and improved environmental risk management for cyclosiloxanes in leather chemicals.
Related standards
- ISO 3696 - Water for analytical laboratory use (normative reference cited in EN ISO 23649:2025).
- Prepared by IULTCS in collaboration with CEN/TC 289 (Leather).
