Overview
EN ISO 19071:2016 / ISO 19071:2016 specifies a chemical test method for the determination of chromium (VI) content and the reductive potential of chromium tanning agents used in leather manufacture. Published by ISO and adopted by CEN, this standard provides a validated laboratory procedure for accurate chromium (VI) measurement where reducing substances in commercial tanning agents can affect recoveries.
Key topics and requirements
- Scope: Determination of Cr(VI) in chromium tanning agents; results indicate the agent’s reductive potential.
- Principle: Dissolve the tanning agent in water, react Cr(VI) with 1,5‑diphenylcarbazide to form a coloured complex, extract the complex into n‑hexanol, and measure absorbance by photometry at 540 nm.
- Standard addition procedure: Because reducing substances can lower measured Cr(VI) recovery, the method uses the standard addition technique (multiple spiked levels) to correct for reductive interference.
- Sample preparation: Homogenize product; solid samples powdered if necessary. Typical mass and dilution steps are specified for reproducible results.
- Reagents and apparatus: Analytical-grade reagents (e.g., phosphoric acid, diphenylcarbazide, potassium dichromate stock), separation funnel, horizontal shaker, spectrophotometer and 20 mm cell (or equivalent).
- Quality control: Daily recovery check with a 15 µg Cr(VI) control; calibration curve levels typically 5, 10, 20, 25, 35 µg Cr(VI). Water for analytical use in accordance with ISO 3696 is normative.
- Reporting: Results expressed as Cr(VI) content and commentary on reductive potential of the tanning agent.
Practical applications and users
- Leather tanneries and chemical suppliers use EN ISO 19071:2016 for product quality control of chromium tanning agents.
- Analytical and testing laboratories implement the method to quantify Cr(VI) for compliance testing and material characterization.
- Regulatory and compliance teams rely on the standard to support obligations under chemical regulations (e.g., REACH) by demonstrating accurate Cr(VI) measurement in the presence of reducing agents.
- R&D and formulation teams can use results to evaluate stabilisation, storage effects, and the reductive behaviour of tanning formulations.
Related standards
This standard is essential where sensitive and interference‑aware measurement of chromium (VI) in leather tanning products is required. Keywords: EN ISO 19071:2016, ISO 19071:2016, chromium (VI), chromium tanning agents, reductive potential, leather chemical tests, standard addition procedure.