Overview
ISO 5517:1978 specifies a photometric procedure for the determination of iron content in fruits, vegetables and derived products using the 1,10‑phenanthroline complex. The method is based on decomposition of organic matter, chemical reduction of ferric iron to ferrous form, formation of a stable red-coloured iron(II)/1,10‑phenanthroline complex in a buffered medium, and photometric measurement at 508 nm.
This standard is intended for analytical laboratories performing routine assays, quality control and compositional analysis of plant‑based foods.
Key Topics
- Principle: Decompose sample matrix, reduce Fe(III) with hydroxyammonium chloride, complex Fe(II) with 1,10‑phenanthroline and measure absorbance at 508 nm.
- Reagents (as specified):
- Hydroxyammonium chloride (chlorhydrate d’hydroxylamine)
- 1,10‑Phenanthroline solution (10 g/L) or corresponding hydrochloride
- Standard iron solution for calibration (e.g., 0.020 g/L prepared from certified sources)
- Acids (sulfuric, nitric, hydrochloric) and acetate buffer components for pH control
- pH control: Colour intensity is stable and reproducible in a buffered pH range around 3.5–4.5; the buffer volume is adjusted in a preliminary test.
- Apparatus: Standard laboratory glassware, analytical balance, Kjeldahl flask (for wet digestion), spectrophotometer/photocolorimeter capable of readings at 508 nm, pipettes and volumetric flasks.
- Calibration and quality control: Establish a calibration curve using a series of iron standards and include a reagent blank. Duplicate determinations are recommended for each sample.
Applications
- Food quality and safety laboratories: Routine quantification of iron in fresh and processed fruits and vegetables.
- Nutritional analysis: Support compositional labeling, dietary studies and fortification monitoring.
- Process control: Monitor raw material and product iron content during production of derived fruit and vegetable products.
Practical advantages include a straightforward photometric workflow, use of well‑established reagents, and suitability for routine laboratory environments. The method integrates with typical sample decomposition routes (wet digestion or ashing followed by dissolution).
Related Standards
- ISO 5515 - Fruits, vegetables and derived products - Decomposition of organic matter (wet digestion)
- ISO 5516 - Fruits, vegetables and derived products - Decomposition of organic matter (incineration)
These referenced standards describe the sample decomposition procedures that feed into ISO 5517:1978. For reliable results follow prescribed sample preparation, calibration, blank correction and replicate testing, and report results with full method details in the test record.