Overview
ISO 19071:2016 - Leather - Chemical tests - Determination of chromium (VI) and the reductive potential for chromium tanning agents - specifies a validated laboratory method to determine chromium (VI) content in chromium tanning agents and to quantify the agent’s reductive potential. The standard is intended for analytical laboratories, leather manufacturers, chemical suppliers and regulatory compliance testing (e.g., REACH).
Key topics and technical requirements
- Scope and purpose: Measurement of Cr(VI) in chromium tanning agents and assessment of reductive potential that can reduce Cr(VI) recovery.
- 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 determine absorbance by photometry at 540 nm.
- Standard addition procedure: Because many tanning agents contain reducing substances, ISO 19071 requires the standard addition method - repeating the test with incremental added Cr(VI) to determine true Cr(VI) and the reductive potential.
- Reagents and apparatus: Analytical-grade reagents including diphenylcarbazide, n‑hexanol, phosphoric acid; equipment such as separation funnel, horizontal shaker (≈250 r/min), spectrophotometer (540 nm) and photometric cell (20 mm typical).
- Sampling and sample prep: Homogenize samples; solids powdered if necessary; prepare analytical solution and analyze immediately.
- Quality control and calibration: Daily recovery check (control sample 15 µg Cr(VI)) and calibration curve (5–35 µg Cr(VI) levels) are required.
- Calculation and reporting: Use linear regression of absorbance vs. added Cr(VI)/sample amount. If calculated Cr(VI) is positive, report the content in mg/kg to 0.1 mg/kg. If negative (common), report Cr(VI) as “less than 3 mg/kg (