Overview
ISO 11212-2:1997 specifies a laboratory method for the determination of mercury (Hg) in starch and derived products by atomic absorption spectrometry (AAS) using cold‑vapour generation. The standard covers sample digestion, reduction of Hg2+ to elemental mercury, cold‑vapour collection and AAS measurement at 253.7 nm, with results expressed as micrograms of mercury per kilogram of product (μg/kg). It also includes guidance on calibration, blanks, safety precautions and reporting.
Key topics and requirements
- Sample preparation and digestion: Wet digestion of the organic matrix using nitric acid and hydrogen peroxide, performed in a reflux/soxhlet-style digestion assembly to avoid loss of volatile mercury.
- Reduction and cold‑vapour generation: Reduction of Hg2+ to metallic Hg using sodium borohydride or tin(II) chloride; cold‑vapour generators vary by design and operators must optimize conditions for their apparatus.
- Instrumentation: High-resolution atomic absorption spectrometer with a mercury discharge or hollow‑cathode lamp, cold‑vapour generator and a quartz measuring cell; absorbance measured at 253.7 nm.
- Calibration and quantification: At least five calibration solutions prepared from a 1 g/L mercury standard; calibration curves plotted from μg/L vs. absorbance (maximum or integrated).
- Quality control and blanks: Include a procedural blank (digesting water) and follow strict glassware cleaning (e.g., nitric acid rinse) to avoid contamination.
- Safety: Explicit warning about mercury toxicity and volatility - verify glassware tightness and avoid overheating during digestion.
- Performance and precision: Annex A reports results of an interlaboratory trial (12 laboratories) providing repeatability and reproducibility guidance for corn starch matrices. The method’s limit of quantification can reach about 20 μg/kg under the stated conditions.
Applications and users
This standard is intended for:
- Food and ingredient testing laboratories performing heavy metal analysis of starches and derivatives.
- Quality control and compliance teams in starch manufacturing, food processing, and ingredient supply chains.
- Regulatory and public‑health laboratories monitoring mercury contamination in foodstuffs.
- Analytical chemists validating and standardizing AAS cold‑vapour methods for organic matrices.
Practical benefits include standardized sample handling, validated calibration procedures, and interlaboratory precision benchmarks useful for certification, regulatory compliance and routine quality assurance.
Related standards
- ISO 11212-1: Determination of arsenic by AAS
- ISO 11212-3: Determination of lead by AAS with electrothermal atomization
- ISO 11212-4: Determination of cadmium by AAS with electrothermal atomization
- ISO 5725 (referenced): Precision of test methods - interlaboratory testing (used for precision evaluation)
Keywords: ISO 11212-2:1997, starch, mercury determination, heavy metals, atomic absorption spectrometry, cold‑vapour AAS, sample digestion, calibration, μg/kg.