ISO 19242:2021

Overview

ISO 19242:2021 specifies a laboratory method for determining the total sulfur content in raw, unvulcanized or vulcanized rubber using ion chromatography. The standard covers sample preparation by either a tubular furnace combustion or an oxygen combustion flask method, conversion of combustion products to sulfate, chromatographic determination of sulfate and conversion of sulfate results to total sulfur content. ISO 19242 replaces the older titration-based methods (e.g., thorin) with a safer, more accurate ion-chromatographic technique.

Key Topics and Requirements

• Scope and applicability: Method applies to raw rubber and rubber compounds. The tubular furnace combustion method is recommended for rubbers with sulfur < 0.1% because the oxygen flask method may lack sufficient accuracy at low levels. The oxygen combustion flask method is not suitable for rubbers containing metal salts that form insoluble sulfates (e.g., barium sulfate).
• Principle: Sulfur in the sample is oxidized to SO2 during combustion, absorbed into hydrogen peroxide, converted to sulfate (SO4 2−) and quantified by ion chromatography.
• Reagents: Analytical-grade reagents and Type 1 water (ISO 3696). Examples include hydrogen peroxide and certified sulfate standard solutions traceable to national standards.
• Apparatus: Combustion furnace or oxygen flask setup, quartz tube, absorbing vessel, and an ion chromatograph (pump, injection valve, anion-exchange column, optional suppressor, conductivity detector). Flow rates, column and eluent selection are addressed (see Annex C for example conditions).
• Procedure: Prepare two independent sample solutions per sample (Annex A for tubular furnace, Annex B for oxygen flask). Generate calibration curve from sulfate standards and measure sample and blank peak areas.
• Calculations & Reporting: Convert sulfate concentration to sulfur content and report average of duplicate analyses, with method details (combustion method used, ion chromatography system, column and eluent) included in the test report.
• Precision: Method precision data available from interlaboratory testing (Annex D).

Applications and Who Uses It

• Quality control laboratories in rubber manufacturing and compounding facilities monitoring sulfur levels for vulcanization control.
• Third‑party testing labs performing regulatory or customer compliance testing on rubber products and raw materials.
• R&D teams developing formulations where precise sulfur determination affects performance.
• Environmental and safety labs replacing hazardous arsenic-based titrations with ion chromatography for safer, eco-friendlier analysis.

Keywords: ISO 19242:2021, total sulfur content, rubber testing, ion chromatography, tubular furnace combustion, oxygen combustion flask, sulfate determination, sulfur analysis.

Related Standards

• ISO 1795 - Sampling and preparative procedures for raw rubber
• ISO 3696 - Water for analytical laboratory use
• ISO 4661-2 - Preparation of samples and test pieces - Part 2: Chemical tests