Overview
ISO 23649:2025 - Chemicals for the leather tanning industry - Determination of cyclosiloxanes - specifies a validated analytical method to identify and quantify the total content of three cyclosiloxanes commonly used in leather chemicals: octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6). The standard requires gas chromatography (GC) coupled with a single-quadrupole mass spectrometer (GC‑MS) and covers sampling, sample preparation, extraction, instrumental analysis, calculation of results and reporting.
Key topics and requirements
- Analytes: D4, D5 and D6 (cyclosiloxanes) in chemicals for the leather tanning industry.
- Analytical principle: Solubilize test specimen in water, perform a liquid–liquid extraction with a 50:50 n‑hexane/ethyl acetate solvent, and analyse extracts by GC‑MS using external calibration and an internal standard to correct recovery and matrix effects.
- Instrumentation: Single quadrupole MS coupled to GC; examples of chromatographic conditions (column type, injection, temperature program) are provided in Annex A as guidance.
- Sample types: Procedure in main body applies to water‑soluble chemicals; Annex C gives sample preparation for non‑water‑soluble chemicals.
- Quality controls: Use of stock and calibration solutions, internal standard (e.g., naphthalene‑D8 or tetrakis(trimethylsilyloxy)silane), filtration, centrifugation and recovery checks.
- Performance: Method can achieve limits of quantification (LoQ) below 50 mg/kg for each cyclosiloxane.
- Reporting: Test report must reference ISO 23649:2025 and include sample description, date, GC equipment, mass fractions (mg/kg), deviations and observations.
Practical applications and users
ISO 23649:2025 is designed for:
- Analytical and contract testing laboratories performing routine screening and quantification of cyclosiloxanes in leather chemicals.
- Leather manufacturers and tanneries for quality control of silicone‑based fatliquors and finishing agents.
- Chemical suppliers verifying product composition and compliance before shipment.
- Regulatory bodies and compliance teams monitoring substances classified as persistent, bioaccumulative and toxic (PBT) in the EU.
Typical uses include supplier audits, regulatory compliance testing, environmental risk assessment and product safety dossiers.
Related standards
- ISO 3696 - Water for analytical laboratory use (referenced normative standard for water quality used in sample preparation).
- Prepared in collaboration with IULTCS and CEN (relevant to leather testing communities).
Keywords: ISO 23649:2025, cyclosiloxanes, D4 D5 D6, GC‑MS, leather tanning, liquid‑liquid extraction, internal standard, LoQ, analytical method.
