Overview
ISO/TS 6733:2006 / IDF/RM 133:2006 specifies a validated analytical procedure for the quantitative determination of lead (Pb) in milk and milk products. The method uses graphite furnace atomic absorption spectrometry (GF-AAS) after mineralization of the sample. It is published as an ISO Technical Specification and IDF Reviewed Method to keep the method available while further interlaboratory validation is completed.
Key topics and technical requirements
- Scope: Total lead content in liquid and solid dairy matrices.
- Detection limits: Approximately 0.001 mg/kg for liquid products and 0.01 mg/kg for solids when dry ashing is used. Pressurized wet mineralization gives similar limits for small test portions (0.2 g dry matter); microwave digestion can lower detection limits by allowing larger test portions.
- Sample mineralization options:
- Programmed dry ashing with sulfuric acid as an ashing aid
- Pressurized wet mineralization (nitric acid) in Teflon or quartz vessels
- Microwave wet mineralization
- Measurement principle: Measurement at 283.3 nm by GF-AAS with Zeeman or deuterium-arc background correction.
- Calibration and quantification: Calibration graph or standard additions; automated and manual calculation procedures are described.
- Reagents and matrix modifiers: High-purity nitric and sulfuric acids; matrix modifiers such as ammonium dihydrogen phosphate, magnesium nitrate, and palladium/magnesium mixtures are specified to improve atomization and reduce interferences.
- Apparatus: Clean quartz crucibles, programmable muffle furnace, analytical balance, autosampler-equipped atomic absorption spectrometer with electrothermal atomizer (graphite tubes/L'vov platforms), and contamination-free digestion vessels.
- Quality and reporting: The technical specification includes guidance on sampling, precision (interlaboratory trials summarized in annexes), and test reporting.
Applications and users
- Routine testing of raw milk, processed dairy products and powders for regulatory compliance and food safety monitoring.
- Quality control laboratories in the dairy industry and contract testing labs performing heavy-metal screening.
- Public health and regulatory agencies establishing or enforcing maximum levels for lead in dairy.
- Reference and research laboratories developing or comparing analytical methods for heavy metals in food.
Related standards
- ISO 3696 - Water for analytical laboratory use (reagents and purity)
- ISO 648, ISO 1042 - Laboratory glassware specifications
- ISO 6732 (IDF 103A) - Related spectrometric methods (iron in milk)
- Published jointly as ISO/TS 6733:2006 and IDF/RM 133:2006
This specification is essential reading for laboratories implementing GF-AAS lead analysis in dairy, offering a complete procedural framework for sample preparation, instrument setup, calibration and data reporting.