ISO 26603:2017

Overview

ISO 26603:2017 - Plastics - Aromatic isocyanates for use in the production of polyurethanes - Determination of total chlorine specifies analytical methods for measuring total chlorine in aromatic isocyanates. The standard converts organically bound chlorine to ionic chloride by combustion and quantifies chloride potentiometrically by titration with silver nitrate (AgNO3). The difference between total chlorine (ISO 26603) and hydrolyzable chlorine (ISO 15028) provides an indicator of residual chlorinated process solvents in isocyanate products. ISO 26603:2017 is technically equivalent to ASTM D4661–03.

Key topics and technical requirements

• Scope and purpose: Determines total chlorine in aromatic isocyanates used for polyurethane production; applicable also to other organic compounds (sample size may need adjustment).
• Two validated test methods:
  • Test Method A - combustion in a pressurized oxygen bomb (detailed apparatus, ignition, and sample handling).
  • Test Method B - combustion in a Schöniger oxygen flask at atmospheric pressure.
• Analytical principle: Complete oxidative destruction of organic matrix to convert organically bound chlorine to chloride, followed by potentiometric titration with AgNO3.
• Reagents and quality: Reagent-grade chemicals; water quality per ISO 3696; specifications reference ISO 6353 series.
• Interferences: Halides and other species that react with silver (e.g., bromide, iodide, thiocyanate, cyanide, sulphide) or reducing agents can interfere with the silver titration.
• Sampling and safety: Special precautions for moisture-sensitive isocyanates - blanket samples with dry inert gas; strict handling, ventilation, and protective equipment guidance.
• Documentation: Procedures include calculation methods, precision and bias data, and required test reporting content.

Applications and who uses it

• Quality control laboratories in polyurethane and isocyanate manufacturing to monitor residual chlorinated solvents and product purity.
• Research laboratories performing compositional analysis of aromatic and aliphatic isocyanates.
• Regulatory and compliance teams assessing product conformance and process cleanliness.
• Practical uses include assessing solvent removal efficiency, batch release testing, and investigating process deviations indicated by elevated residual chlorine.

Related standards

• ISO 15028 - Hydrolyzable chlorine in isocyanates (used together to quantify residual solvents).
• ISO 3696 - Water for analytical laboratory use.
• ISO 6353-2 / ISO 6353-3 - Reagent specifications.
• ASTM D4661–03 - Technical equivalent.

Keywords: ISO 26603:2017, total chlorine, aromatic isocyanates, polyurethanes, oxygen bomb, Schöniger flask, silver nitrate titration, hydrolyzable chlorine, quality control.