Overview
ISO 3856-7:1984 - Paints and varnishes - Determination of “soluble” metal content - Part 7 specifies a flameless (cold vapour) atomic absorption spectrometric method for measuring mercury in paint test solutions. The method covers the pigment portion of paints (including powder form) and the liquid portion of water-dilutable paints. The analytical range is approximately 0.005 % (m/m) to 0.05 % (m/m) soluble mercury.
The principle: oxidize or combust mercury compounds to convert mercury to Hg(II), chemically reduce to elemental mercury, entrain mercury vapour in a carrier gas and measure the monoatomic vapour by cold vapour atomic absorption at about 253.7 nm.
Key topics and technical requirements
- Sample types: pigment portion (acid extracts) and liquid portion from water-dilutable paints.
- Sample preparation: acid extraction (referenced to ISO 6713), oxidation (e.g., potassium permanganate), and combustion of residue for liquid-phase concentrates.
- Detection principle: reduction of Hg(II) to elemental mercury and measurement by cold vapour atomic absorption spectrometry (CV-AAS) at ~253.7 nm.
- Analytical range: suitable for soluble mercury contents ≈ 0.005–0.05 % (m/m).
- Reagents and materials (examples from the method): sulfuric and nitric acids, potassium permanganate, tin(II) chloride reducing agent, hydroxylammonium chloride, mercury standard solutions.
- Apparatus: atomic absorption spectrometer with mercury cold-vapour cell, quartz measuring cell (≥100 mm path), combustion flask, rotary evaporator, flowmeter and pump, and spark generator for sample ignition.
- Calibration & quality control: prepare standard matching solutions on day of use; plot peak height/area vs. mass of Hg; include blank determinations and duplicate analyses.
- Safety: mercury and certain reagents are toxic/corrosive - perform work in a well-ventilated fume cupboard and follow laboratory safety rules.
Practical applications
- Routine quality control for paint and varnish manufacturers to monitor soluble mercury in pigments and formulations.
- Independent analytical and environmental laboratories assessing mercury content in coatings for regulatory compliance.
- Product safety assessment and formulation development where control of heavy metals is required (consumer, architectural, industrial coatings).
Who should use this standard
- Analytical chemists in coatings laboratories
- QA/QC teams in paint manufacturing
- Environmental testing services and regulatory bodies overseeing heavy-metal limits in coatings
Related standards
- ISO 6713 - Paints and varnishes: preparation of acid extracts from paints
- ISO 3696 - Water for laboratory use (purity grades)
- Other parts of ISO 3856 - Determination of “soluble” metal content in paints and varnishes
Keywords: ISO 3856-7:1984, paints and varnishes, mercury determination, cold vapour AAS, flameless atomic absorption, soluble metal content, pigment analysis, water-dilutable paints.