ISO 5398-3:2018

Overview

ISO 5398-3:2018 - Leather - Chemical determination of chromic oxide content - Part 3: Quantification by atomic absorption spectrometry defines a laboratory method to determine total chromium in leather samples by atomic absorption spectrometry (AAS). The method reports chromium as chromic oxide (mg/kg, dry matter) and applies to leathers expected to contain more than 5 mg/kg chromium. Two sample‑preparation routes are specified (wet oxidation and microwave digestion); the wet‑oxidation technique is mandatory in case of dispute.

Key topics and technical requirements

• Scope: Total chromium determination in aqueous extracts from leather; not compound‑ or oxidation‑state specific.
• Sampling and sample preparation: Follow ISO 2418 for sampling location and ISO 4044 for preparing chemical test samples. Typical test mass is 2 g and at least two determinations per sample are required.
• Sample digestion:
  • Wet oxidation using nitric acid followed by a sulfuric/perchloric acid mix (add nitric acid first for safety).
  • Microwave‑assisted digestion (MAD) per EN 14602 is an alternative technique.
• Reagents: Analytical‑grade acids (nitric; sulfuric/perchloric mix), potassium dichromate standard (certified solution recommended), and potassium chloride matrix solution with a trace of nitric acid.
• Instrumentation: Atomic absorption spectrophotometer with appropriate hollow‑cathode lamp and nitrous‑oxide burner (Annex B gives example settings: wavelength 357.9 nm, slit 0.5 nm, red cone flame recommended). Filtration (glass‑fibre or membrane) and standard laboratory glassware required.
• Calibration and measurement: Calibration curve prepared from standard dichromate solutions (2–8 µg/ml Cr). Test solutions filtered and diluted as necessary (target ≤ 7.5 µg/ml Cr for direct analysis).
• Calculation: Convert measured Cr concentration to chromic oxide using the factor 1.462 and correct for volatile matter (factor F calculated from ISO 4684 volatile‑matter results).
• Reporting: Include method reference (ISO 5398‑3), leather description, sample prep/digestion details, volatile matter (%), results (mg/kg), and deviations.

Applications and users

This standard is essential for:

• Leather testing laboratories and tanneries performing chromium content analysis for quality control and process monitoring.
• Manufacturers of footwear, garments and leather goods requiring compliance checks.
• Environmental, regulatory and compliance bodies assessing chromium levels in leather products and waste streams.
• R&D teams developing low‑chrome or chrome‑free tanning processes and validating analytical performance.

Keywords: ISO 5398-3, chromic oxide, chromium determination, atomic absorption spectrometry, leather testing, wet oxidation, microwave digestion, AAS calibration.

Related standards

• ISO 5398 series (other parts for chromic oxide determination)
• ISO 2418 (sampling location)
• ISO 4044 (sample preparation)
• ISO 4684 (volatile matter)
• ISO 3696 (water for analytical use)
• EN 14602 (microwave digestion guidance)