Overview
ISO 1657:1986 - "Rubber, raw and rubber latex - Determination of iron content - 1,10‑Phenanthroline photometric method" defines a spectrophotometric procedure to quantify iron (Fe) in uncompounded raw natural and uncompounded synthetic rubbers (that do not contain chlorine) and their corresponding uncompounded latices. The method covers sample preparation, calcination of rubber or dried latex, acid digestion, reduction of iron, complexation with 1,10‑phenanthroline, and photometric measurement. The working range specified is 5 to 1 000 mg/kg (ppm) of iron.
Key topics and technical requirements
- Scope: Uncompounded natural and specified synthetic rubbers and latices; iron content 5–1 000 mg/kg.
- Principle: Calcine sample → dissolve ash in hydrochloric acid → reduce Fe(III) to Fe(II) with hydroxylammonium chloride → form an orange‑red Fe(II)-1,10‑phenanthroline complex → measure absorbance near 510 nm.
- Reagents & standards: Analytical‑grade HCl (density 1.19 g/cm3), 1,10‑phenanthroline solution, hydroxylammonium chloride solution, acetate buffer, and Fe standard solutions (mother and working standards described).
- Apparatus: Muffle furnace (approx. 550 ± 25 °C), silica or porcelain crucibles, colorimeter/spectrophotometer with 5 cm cuvettes, glassware (50 cm3 volumetric flasks, pipettes).
- Sample preparation: Homogenized thin sheet for raw rubber (ISO 1796), dried latex sheet for latex (ISO 124); precautions to avoid Fe contamination (no rusted tools; use chromed or non‑iron contact surfaces).
- Calibration & blanks: Prepare calibration curve using Fe working standards; run procedural blank in parallel and apply blank correction to photometric readings.
- Safety & safeguards: Avoid overheating (risk of Fe loss in silica crucibles), do not open furnace during initial hour, prevent contamination from equipment.
Applications and users
- Quality control and incoming raw material inspection in rubber manufacturing.
- Analytical laboratories performing trace iron analysis in elastomers and latex.
- Raw material suppliers and compounders monitoring metal contamination that can affect vulcanization, color, and product performance.
- Research and regulatory labs concerned with material compliance and failure analysis.
Related standards
- ISO 123 - Latex sampling
- ISO 124 - Latex - Determination of total solids
- ISO 1795, ISO 1796 - Raw rubber sampling and sample preparation
- ISO 4793 - Laboratory sintered glass filters
- ISO 6665 - General iron determination methods (spectrophotometric with phenanthroline)
Keywords: ISO 1657:1986, rubber iron determination, 1,10‑phenanthroline, photometric method, raw rubber testing, latex iron analysis, spectrophotometric iron assay, trace metal in rubber.