Overview
ISO 6332:1988 specifies a spectrometric method using 1,10-phenanthroline for the determination of iron in water and wastewater. The standard covers procedures for measuring:
- Total iron (direct or after decomposition),
- Total dissolved iron (Fe(II) + Fe(III)), and
- Dissolved iron(II).
Applicable concentration range is 0.01–5 mg/L (samples above 5 mg/L should be diluted). The method is based on forming an orange-red Fe(II)-1,10-phenanthroline complex and measuring absorbance at about 510 nm.
Key topics and technical requirements
- Reagents: analytical-grade sulfuric, nitric and hydrochloric acids; acetate buffer; hydroxylammonium chloride (reducing agent); 1,10-phenanthroline reagent; potassium peroxodisulfate (oxidant); iron stock and standard solutions.
- Apparatus: spectrometer (prism or grating) set near 510 nm, photometric cells (optical path ≥ 10 mm recommended), 0.45 µm membrane filters, and a 100 mL oxygen (Winkler) flask for some procedures.
- Sample handling: follow ISO 5667-1 sampling guidance; acidify samples to pH 1 immediately after collection to stabilize iron and avoid oxidation/precipitation.
- Analytical procedure:
- For total iron: direct test or chemical decomposition (HNO3 + HCl, followed by SO3 fumes evaporation) then oxidation (K2S2O8 boiling or autoclave) if needed.
- Reduce Fe(III) to Fe(II) with hydroxylammonium chloride; adjust pH to 3.5–5.5 with acetate buffer; add 1,10-phenanthroline and incubate in the dark ~15 min.
- Measure absorbance at ~510 nm against a blank and calculate concentration using calibration curves.
- Calibration & quality control: prepare series of reference solutions; generate separate calibration curves for each iron form, instrument and cell path length; check calibration frequently and for each new reagent batch.
- Reporting & precision: specified reporting resolution (e.g., 0.001 mg/L for 0.010–0.100 mg/L). Precision data and repeatability are given in the standard.
- Interferences & safety:
- Potential interferences: Cu, Co, Cr, Zn (when ≥10× iron); Ni (>2 mg/L); Bi, Ag, Hg (>1 mg/L); Cd (>50 mg/L); cyanides and sulfides require care.
- Warning: acidification can release toxic gases-take appropriate safety precautions.
Applications and users
ISO 6332 is used by:
- Environmental and municipal water laboratories,
- Wastewater treatment facilities,
- Regulatory agencies monitoring compliance with water quality limits,
- Research laboratories studying iron chemistry in aquatic systems.
Practical applications include routine monitoring of drinking water, surface water, groundwater and wastewater streams to assess corrosion, treatment efficiency, and ecological impacts.
Related standards
- ISO 5667-1 - Water quality - Sampling: guidance referenced in ISO 6332 for sample collection and handling.