ISO 5398-2:2009

Overview

ISO 5398-2:2009 is an international standard establishing a colorimetric method for the chemical determination of chromic oxide content in leather. This method is specifically designed for leathers expected to contain chromic oxide in excess of 0.05%. It provides a standardized approach for quantifying total chromium content without differentiating chromium compounds or oxidation states.

The standard complements other parts of ISO 5398, which cover titration, atomic absorption spectrometry, and inductively coupled plasma optical emission spectrometry methods. ISO 5398-2 focuses on practical colorimetric analysis using spectrophotometry, making it suitable for industrial and laboratory applications where chromic oxide levels need reliable and accurate determination.

Key Topics

• Scope: Quantifies total chromium, expressed as chromic oxide (Cr₂O₃), in dry leather via colorimetric determination.
• Sampling and Preparation: Requires grinding leather samples and accurate weighing (typically 0.75 g) following ISO 2418 (sampling location) and ISO 4044 (sample preparation).
• Analytical Principle:
  • Leather ash is fused using an alkaline mixture.
  • Chromium is solubilized in hexavalent form and reacts with 1,5-diphenyl carbazide.
  • The resulting colored complex is measured photometrically at 540 nm.
• Reagents: Use of high-grade chemicals including sodium and potassium carbonates, sodium tetraborate for fusion; sulfuric acid; potassium dichromate as standard; and diphenyl carbazide as the color reagent.
• Apparatus: Standard laboratory equipment such as a muffle furnace, porcelain or platinum crucibles, spectrophotometer capable of precise absorbance readings, and filtration devices.
• Method Steps:
  • Ashing leather samples at ~750 °C.
  • Alkaline fusion of ash.
  • Dissolution, acidification, and preparation of the test solution.
  • Colorimetric reaction by addition of diphenyl carbazide.
  • Absorbance measurement against calibration standards.
• Calibration and Validation: Construction of a calibration curve through potassium dichromate standards; routine system checks to ensure method accuracy.
• Calculation: Determining chromic oxide content considering sample mass, dilution factors, and volatile matter content (corrected by ISO 4684).
• Repeatability: Duplicate tests should vary by no more than 0.1% Cr₂O₃, ensuring method reliability.
• Reporting: Test reports must include standard reference, leather description, methodology details, volatile matter content, test results with appropriate precision, and any procedural deviations.

Applications

• Leather Industry Quality Control: Enables tanneries and leather manufacturers to monitor chromium content in raw and processed leathers, ensuring compliance with product specifications and regulatory limits.
• Environmental and Health Compliance: Accurate chromium quantification helps assess potential environmental impacts and occupational safety related to chromium in leather goods.
• Research and Development: Supports development of new leather treatments and testing protocols by providing a reliable chemical analysis method for chromium content.
• Standardized Testing Laboratories: Provides laboratories with a validated procedure that aligns with international standards for chromic oxide determination.

Related Standards

• ISO 5398-1: Chemical determination of chromic oxide content - Quantification by titration
  An alternate method focusing on titrimetric analysis of chromium in leather.

• ISO 5398-3: Chemical determination of chromic oxide content - Quantification by atomic absorption spectrometry
  A more sensitive instrumentation-based technique using atomic absorption.

• ISO 5398-4: Chemical determination of chromic oxide content - Quantification by ICP-OES
  Employs inductively coupled plasma optical emission spectroscopy for chromium quantification.

• ISO 2418: Leather - Chemical, physical and mechanical and fastness tests - Sampling location
  Guidance on appropriate leather sampling for testing.

• ISO 4044: Leather - Chemical tests - Preparation of chemical test samples
  Defines preparation methods of leather samples for chemical analysis.

• ISO 4684: Leather - Chemical tests - Determination of volatile matter
  Method for determining moisture and volatile components in leather samples.

• ISO 3696:1987: Water for analytical laboratory use - Specification and test methods
  Specifies water quality requirements for analytical reagents and processes.

Keywords: ISO 5398-2, chromic oxide content, leather chemical analysis, colorimetric determination, chromium quantification, leather testing standards, spectrophotometric analysis, leather quality control, chromium in leather, leather testing methods.