Overview
ISO 6503:1984 specifies a laboratory method for the determination of total lead in paints and varnishes using flame atomic absorption spectrometry (AAS). The standard covers sample decomposition by one of two preparative routes - dry ashing or wet oxidation - followed by measurement of lead absorption at 283.3 nm. The method is intended primarily for coating materials with total lead contents of about 0.01% (m/m) to 2% (m/m), although it may be applied to higher concentrations when required precision is met.
Key topics and requirements
- Scope and applicability
- Target range: ~0.01% to 2% (m/m) total lead; possible use above 2% if precision remains acceptable.
- Two preparative methods provided; the dry ashing method is the referee (preferred in disputes).
- Sample preparation
- Dry ashing: evaporate to dryness, ash at 475 °C, extract residue with hydrochloric acid.
- Wet oxidation: oxidize organics with sulfuric acid + hydrogen peroxide (method A) or sulfuric + nitric acid in a Kjeldahl flask (method B); extract lead with EDTA + ammonia.
- Procedures include reagent blanks, aliquot selection based on expected lead content, and duplicate testing.
- Reagents and apparatus
- Typical reagents: HCl, HNO3, H2SO4, H2O2, EDTA, ammonia; water conforming to ISO 3696.
- Equipment: flame AAS system, lead hollow‑cathode or discharge lamp, acetylene/air burner, muffle furnace, silica crucibles.
- Measurement and calibration
- AAS measurement at 283.3 nm; aspiration into an acetylene/air flame.
- Use standard matching solutions and construct a calibration graph (mass of Pb per ml vs absorbance, blank-corrected).
- Quality and precision
- Follow ISO guidance on precision and inter-laboratory reproducibility (ISO 5725 referenced).
- Dry ashing recommended as referee method when sample composition or interference (e.g., antimony, cellulose nitrate) is a concern.
Applications and users
- Laboratories performing quality control for paint and coating manufacturers.
- Regulatory and compliance testing for lead content in consumer coatings and protective coatings.
- Environmental and public health testing labs monitoring lead in building materials.
- Inspection bodies and third-party testing services validating supplier declarations.
Related standards
Keywords: ISO 6503, total lead, paints and varnishes, flame atomic absorption spectrometry, lead determination, dry ashing, wet oxidation, AAS, 283.3 nm, sample preparation, regulatory compliance.