Overview
ISO 6561-2:2005 specifies a validated laboratory method for the determination of cadmium content in fruits, vegetables and derived products using flame atomic absorption spectrometry (FAAS). This part of ISO 6561 complements ISO 6561-1 (graphite furnace AAS) and is based on AOAC procedures. The standard covers sample preparation, chemical reagents, instrumental settings, calculation and precision data required for reliable cadmium analysis.
Key topics and technical requirements
- Scope: Determination of cadmium in fruit and vegetable matrices and processed products by FAAS.
- Sample preparation: Representative laboratory sample grinding; typical test portion = 50 g. Frozen products must be thawed and included.
- Decomposition/digestion: Wet digestion of organic matrix using concentrated nitric acid (HNO3), followed by sulfuric acid (H2SO4) and controlled addition of hydrogen peroxide (H2O2) to obtain a colourless digest.
- Extraction chemistry: Complexation and solvent extraction of cadmium using dithizone in chloroform at pH ≈ 8.8 (adjusted with ammonia and monitored with thymol blue). Warning: chloroform is toxic and ozone-depleting - use a fume hood and follow waste-disposal rules.
- Instrumental conditions: FAAS with an air/acetylene burner (10 cm recommended) and measurement at 228.8 nm. Calibration uses cadmium standards (0.1, 0.5, 1.0 and 2.0 µg/ml) prepared in dilute HCl.
- Calibration and measurement: Prepare a calibration graph (absorbance vs µg/ml), measure sample and blank at the same aspiration rate, dilute samples exceeding the highest standard.
- Calculation: Cadmium concentration is derived from the calibration curve, corrected for blank, sample mass and dilution factor.
- Precision: Interlaboratory repeatability and reproducibility values provided from collaborative studies (examples: lettuce and potatoes at levels 0.05–1.5 mg/kg).
Applications and users
- Food testing laboratories analyzing cadmium residues in fresh produce and processed fruit/vegetable products.
- Regulatory agencies and quality control units enforcing maximum cadmium limits in food.
- Research groups studying heavy metal uptake, food safety risk assessment, and agronomy.
- Analysts choosing between FAAS (ISO 6561-2) and higher-sensitivity methods (ISO 6561-1 graphite furnace) depending on required detection limits.
Related standards
- ISO 6561-1: Method using graphite furnace AAS (for lower detection limits)
- AOAC Official Methods of Analysis (basis for procedure)
- ISO 5725 series (precision - repeatability and reproducibility principles)
Keywords: ISO 6561-2:2005, cadmium determination, fruits and vegetables, flame atomic absorption spectrometry, FAAS, dithizone extraction, sample digestion, calibration graph, repeatability, reproducibility.
