ISO 6503:1984

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

• ISO 3856/1 - alternative dithizone spectrophotometric method
• ISO 1512, ISO 1513 - sampling and sample preparation for paints and varnishes
• ISO 3696 - water for laboratory use
• ISO 1042 - volumetric glassware
• ISO 5725 - precision of test methods

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.