Overview
ISO 2992:1974 specifies the 2,2'-bipyridyl photometric method for determining the iron content in industrial-grade ammonium sulphate. This internationally recognized standard, developed by ISO/TC 47 (Chemistry) and approved by IUPAC, applies to iron (Fe) concentrations equal to or greater than 0.0001% (m/m). The method is based on the reduction of iron(III) to iron(II) and the formation of a colored iron(II)-2,2'-bipyridyl complex in a buffered medium with a pH between 4.5 and 6, which is then measured photometrically at approximately 522 nm.
This standard provides a precise, reliable approach for laboratories and industries to quantify trace iron impurities critical to the quality and performance of ammonium sulphate used in various industrial applications.
Key Topics
- Scope: Applicable for ammonium sulphate with iron content ≥ 0.0001% (m/m)
- Principle:
- Reduction of Fe(III) to Fe(II) by hydroxylammonium chloride
- Complex formation between Fe(II) and 2,2'-bipyridyl in pH 4.5-6 buffer
- Photometric measurement of colored complex at ~522 nm wavelength
- Reagents and Solutions:
- Hydroxylammonium chloride (reducing agent)
- 2,2'-bipyridyl solution (complexing agent)
- Ammonium acetate buffer for maintaining pH
- Hydrochloric acid solution
- Standard iron solutions for calibration
- Apparatus:
- Spectrophotometer or electrophotometer equipped with appropriate filters
- Standard laboratory glassware (volumetric flasks, burettes, pipettes)
- Procedure Highlights:
- Sample preparation with precise weighing
- Preparation of calibration curves using standard iron solutions
- Color development by adding reagents in specified order and timing
- Accurate photometric absorbance readings against blanks
- Calculation of iron content expressed as mass percentage (% m/m)
- Quality Control:
- Parallel blank tests to ensure accuracy
- Detailed recording of measurements and anomalies in test reports
Applications
ISO 2992:1974 is essential for industries and laboratories involved in the production, quality control, and certification of industrial ammonium sulphate. Its applications include:
- Fertilizer manufacturing: Monitoring iron impurities which can affect solubility and nutrient delivery.
- Chemical industry: Ensuring purity for processes sensitive to iron contaminants.
- Analytical laboratories: Routine quality assurance of ammonium sulphate batches.
- Environmental monitoring: Detecting trace iron content to comply with regulatory standards related to chemical handling and waste management.
By providing standardized measurement techniques, this ISO ensures consistent, reproducible iron analysis, helping maintain product integrity and regulatory compliance.
Related Standards
ISO 2992:1974 belongs to a series of standards related to testing industrial ammonium sulphate, including:
- ISO 2993: Determination of free acidity in ammonium sulphate by titrimetric method.
- ISO 2994: Measurement of water-insoluble matter by gravimetric method.
- ISO 3332: Quantification of ammoniacal nitrogen via volumetric distillation.
- ISO 3333: Copper content determination (method under development).
These complementary standards facilitate comprehensive quality assessment of ammonium sulphate for industrial purposes, covering a wide range of chemical and physical properties.
Keywords: ISO 2992, ammonium sulphate iron content, 2,2'-bipyridyl photometric method, iron determination, industrial ammonium sulphate analysis, iron impurity measurement, chemical quality control, spectrophotometric iron analysis, ISO standards ammonium sulphate, iron(III) reduction, hydroxylammonium chloride reaction.