Overview
EN ISO 4045:2018 - "Leather - Chemical tests - Determination of pH and difference figure" specifies a standardized laboratory method to determine the pH of an aqueous leather extract and, where required, the difference figure (the difference between the pH of the extract and the pH of its tenfold dilution). Prepared by IULTCS in cooperation with CEN, this method is applicable to all types of leather and is widely used in quality control, conformity testing and R&D.
Key topics and technical requirements
- Scope: Measurement of pH of an aqueous extract; determination of the difference figure if pH < 4.00 or > 10.00.
- Sample preparation: Weigh (5.0 ± 0.1) g leather, add (100 ± 1) ml water (ISO 3696 grade 3) at (20 ± 2) °C, pre-wet 30 s then shake mechanically for 6.0–6.5 h; decant or filter/centrifuge to obtain a clear extract.
- Apparatus: Rotating shaker (≈50 ± 10 r/min) or validated alternative, pH meter with glass electrode (0–14 pH range, 0.01 graduation), analytical balance (0.01 g), 250 ml wide‑mouthed flask, 100 ml volumetric flask/pipette.
- Calibration: Calibrate electrode system before each series using at least two buffer solutions (one below and one above expected pH). Buffer readings must be within 0.02 pH units of the correct value.
- Measurement: Record pH of extract at (20 ± 2) °C after stirring; take reading to nearest 0.05 pH unit within 30–60 s of immersion. For difference figure, dilute 10 ml extract to 100 ml and repeat pH measurement; difference figure = pH (extract) − pH (dilution).
- Accuracy & reporting: Results reported to nearest 0.05 pH unit; analyze samples in duplicate where possible. Test report must reference ISO 4045 and include sample description, pH/difference figures, any instability in readings and deviations from procedure.
- Notes on interpretation: Difference figures range up to 1.00; values ≈0.70–1.00 indicate presence of free strong acid or base in extracts with extreme pH.
Applications and users
- Quality control in tanneries and leather finishing operations
- Independent testing laboratories and certification bodies
- Product development and R&D for leather chemistry and processing
- Suppliers validating chemical treatments, neutralization and finishing processes
- Regulatory or procurement teams requiring standardized pH data
Keywords: EN ISO 4045:2018, leather pH test, difference figure, leather chemical tests, aqueous extract, pH meter, leather quality control.
Related standards
- ISO 2418 - Sampling location for leather tests
- ISO 3696 - Water for analytical laboratory use
- ISO 4044 - Preparation of chemical test samples for leather
This standardized procedure ensures consistent, repeatable pH and difference-figure measurements critical to leather quality, processing control and safety assessments.