Overview - ISO 7158:2024 (Ion chromatography for nitrite/nitrate in meat)
ISO 7158:2024 specifies a validated laboratory method for the determination of nitrite and nitrate in meat and meat products using ion chromatography (IC). The method covers sample preparation, extraction and clarification, chromatographic separation, detection (conductivity or UV/VIS), calculation and performance characteristics (precision, LOD/LOQ). It is intended for routine and compliance testing where accurate quantification of nitrite/nitrate is required.
Key topics and technical requirements
- Scope: Determination of nitrite (NO2–) and nitrate (NO3–) in meat and meat products by ion chromatography.
- Principle: Aqueous extraction, protein precipitation and cleanup, separation on an anion-exchange IC column, and detection by suppressed conductivity or UV at 226 nm using external standards.
- Sampling & sample prep:
- Recommended laboratory-received sample: representative, at least 200 g; homogenize and analyse within 24 h of homogenization.
- Typical test aliquot: 5 g extracted in water, ultrasonic assistance, protein precipitation with potassium ferrocyanide and zinc sulfate, centrifugation and filtration.
- Cleanup uses sequential C, Ag and Na purification columns (solid-phase).
- Chromatography:
- Column: anion-exchange (e.g., 4 mm × 250 mm with 4×50 mm guard) compatible with KOH gradient elution.
- Eluent: potassium hydroxide (6 mmol/L → 70 mmol/L gradient recommended); flow ~1.0 mL/min.
- Injection volume: ~50 µL (adjustable by instrument).
- Detection: suppressed conductivity (detector cell ~35 °C) or UV at 226 nm.
- Standards & calibration: Mixed nitrite/nitrate working standards across recommended ranges; external standard calibration (peak height or area).
- Calculations: Formula provided to convert measured concentration (mg/L) to mg/kg in sample. Conversion factors: multiply measured nitrite ion by 1.5 to report as sodium nitrite, and nitrate ion by 1.37 to report as sodium nitrate.
- Performance:
- Precision parameters reported (repeatability and reproducibility standard deviations for nitrite and nitrate).
- LOD and LOQ are addressed (see clause 7.6 in the standard).
Applications and users
ISO 7158:2024 is applicable for:
- Food testing laboratories performing regulatory compliance, quality control and safety monitoring of processed meats (e.g., cured meats, sausages).
- Manufacturers verifying formulations and residual nitrite/nitrate levels.
- Regulatory agencies and inspection labs assessing compliance with maximum limits.
- Research labs studying curing chemistry or nitrosation risk in meat products.
Keywords: ISO 7158:2024, nitrite and nitrate, meat and meat products, ion chromatography, ion chromatograph, conductivity detector, sample preparation, LOD, LOQ, precision.
Related standards
- ISO 3696 - Water for analytical laboratory use (reagent water quality)
- CAC/GL 50-2004 - Recommended sampling for foods
- ISO 5725-2 - Precision of measurement methods (statistical treatment)