Overview
ISO 6732:2010 / IDF 103:2010 specifies a reference spectrometric method for the determination of iron content in milk and milk products. The method covers a wide range of dairy matrices - from liquid milks, yogurts, whey and buttermilk to concentrated, dried and fat-rich products (cream, butter, anhydrous butterfat, ghee), ice‑cream, cheeses, caseins and processed cheese. Results are conventionally reported as milligrams of iron per kilogram (mg/kg).
Key topics and technical requirements
- Principle: Organic material is digested (nitric + sulfuric acids) with prior fat removal for certain high‑fat products. Ferric iron (Fe3+) is reduced to ferrous iron (Fe2+), complexed with bathophenanthroline, extracted into isoamyl alcohol, and the red complex’s absorbance is measured at 533 nm by spectrometry.
- Sample preparation: Matrix‑specific pre‑treatment (e.g., melting and mixing ice‑cream, serum separation for butter, reconstitution or homogenization for dried milks) to ensure representative test portions.
- Digestion and cleanup: Strong acids, potassium sulfate, hydrogen peroxide and controlled digestion conditions are specified; some matrices require fat separation prior to digestion.
- Reagents and standards: Use of iron‑free reagents where possible; preparation/usage of iron standard solutions (1 000 mg/L and 1 mg/L) for calibration; bathophenanthroline and reducing agents (hydroxylammonium chloride or ascorbic acid).
- Apparatus and contamination control: Use of clean, iron‑free glassware, quartz glass beads, Kjeldahl digestion flasks, centrifuges, and a spectrometer with 10 mm cells. Laboratories must actively avoid rust/iron contamination (e.g., acid cleaning, dedicated glassware).
- Measurement and expression: Spectrometric absorbance measured at 533 nm; iron content expressed as mass fraction (mg/kg).
Applications and users
ISO 6732:2010 is primarily used by:
- Dairy industry quality control and production laboratories for monitoring iron levels in raw materials and finished products.
- Food safety and regulatory laboratories for compliance testing and residue/contaminant surveillance.
- Analytical and research labs conducting nutritional analyses, trace‑metal studies, or method validation.
- Routine use cases include nutritional labeling verification, process control, product formulation checks and investigation of metal contamination sources.
Related standards
- ISO 707 | IDF 50 - Sampling of milk and milk products (recommended sampling methods)
- ISO 3696 - Water for analytical laboratory use (grade 2)
- Associated ISO/IDF methods and laboratory equipment standards referenced within the method (e.g., sieves, pipettes, balances)
Keywords: ISO 6732:2010, iron determination, milk and milk products, spectrometric method, bathophenanthroline, dairy laboratory, trace metals, food analysis, reference method.
Open preview (PDF)Milk and milk products — Determination of iron content — Spectrometric method (Reference method)
