Overview
ISO 23637:2021 specifies a validated laboratory method for the determination of cadmium (Cd) in cereals (rice, brown rice, wheat and maize) by graphite furnace atomic absorption spectrometry (GFAAS) after extraction with diluted nitric acid (HNO3). The method includes sample preparation, extraction, GFAAS measurement (228.8 nm), calibration and quality control. The approximate limit of quantification (LOQ) is 0.002 mg/kg, dependent on matrix and instrument conditions.
Key topics and technical requirements
- Scope and matrices: Applicable to rice, brown rice, wheat and maize. Sampling itself is outside the method but ISO 24333 is recommended for rice sampling.
- Sample preparation: Grinding to specified particle sizes (maize ≤ 0.25 mm; other cereals ≤ 0.40 mm) and homogenous mixing.
- Test portion and extraction: Typical test portion 0.200 g ±0.001 g extracted with 5.0 mL diluted HNO3; centrifuge or stand to obtain supernatant.
- Instrumentation: GFAAS with graphite furnace, autosampler and background correction (e.g., Zeeman). Cadmium hollow cathode lamp at 228.8 nm.
- Calibration: Use external calibration solutions (recommended range ~0.4–2.0 µg/L) and at least four calibration points; linearity check required.
- Matrix modifier: Palladium nitrate (Pd(NO3)2) 100 mg/L recommended as matrix modifier; typically add 5 µL during injection to reduce matrix interferences.
- Quality control and calculation: Analyze certified reference materials (CRM/RM) each run; results calculated to mass fraction (mg/kg) using blank-corrected concentrations and expressed to two significant figures.
- Precision data: Repeatability and reproducibility characteristics are provided (with formulae) based on interlaboratory studies and ISO precision guidance.
Applications and users
- Food safety and public health laboratories monitoring cadmium in cereals and cereal products.
- Regulatory authorities enforcing maximum levels and import/export compliance.
- Commercial testing and contract laboratories providing contaminant screening for processors and retailers.
- Agricultural researchers and cereal processors assessing cadmium uptake, mitigation and quality control.
Related standards
- ISO 3696 - Water for analytical laboratory use (grade 1 water).
- ISO 24333 - Recommended sampling for rice (sampling guidance).
- ISO 5725 series - Methods for determining precision (repeatability and reproducibility) of measurement methods.
ISO 23637:2021 is a practical, instrument-based standard for reliable cadmium quantification in cereals using GFAAS with diluted nitric acid extraction - key for compliance testing, risk assessment and food safety monitoring.