Overview
ISO 6637:1984 specifies a flameless atomic absorption method for the determination of mercury content in fruits, vegetables and derived products. The procedure decomposes organic matter in a sulfuric–nitric acid medium, chemically reduces Hg(II) to metallic mercury with tin(II) chloride, entrains mercury vapour in a circulating air stream and measures absorbance in an enclosed atomic‑absorption (mercury analyser) system.
Key topics and technical requirements
- Scope: Applicable to fruit, vegetable and derived food matrices (liquid, doughy/solid, dehydrated).
- Sample preparation: Homogenize samples (PTFE‑lined mechanical grinder); liquid test portions typically 10 ml, solid test portions about 5 g.
- Decomposition apparatus: Borosilicate glass assembly comprising a modified Soxhlet extractor (200 ml) with stop‑cock, a 75 ml dropping funnel, a 35 cm condenser and a 500 ml round‑bottom flask.
- Reagents: Analytical‑grade sulfuric and nitric acids, urea, tin(II) chloride (100 g/l) and mercury(II) chloride standard solutions (1 g/L and 100 µg/L dilutions). Use mercury‑free distilled water.
- Reduction and entrainment: Add Sn(II) chloride to reduce Hg2+ to Hg0; entrain vapour by air bubbling through a closed circuit to the absorption cell.
- Flameless atomic absorption system: Mercury vapour lamp, absorption cell (25 mm internal diameter, 115 mm length, silica windows), phototube with 253.7 nm filter and read‑out device.
- Calibration and calculation: Six‑point calibration (0–0.5 µg Hg standards), blank correction, and calculation of mercury content in µg/kg or µg/L.
- Quality criteria: Two determinations per sample; repeatability requirement-difference between duplicates should not exceed 10% of the mean.
Applications and users
ISO 6637:1984 is designed for practical use in:
- Food testing and quality control laboratories conducting mercury surveillance in produce and processed vegetable/fruit products.
- Regulatory and public health agencies enforcing contaminant limits and monitoring food safety.
- Food manufacturers and processors performing incoming raw material checks and product compliance testing.
- Research laboratories studying mercury uptake, distribution and removal in plant‑based foods.
Practical benefits include reliable mercury quantification, standardization of sample digestion and measurement workflow, and compatibility with enclosed flameless atomic absorption analysers used for trace mercury analysis.
Related standards
ISO 6637 was developed under ISO/TC 34 (agricultural food products). For broader heavy‑metal testing and atomic absorption techniques, consult other ISO standards and national methods on heavy‑metal determination and AAS/mercury analyser procedures.