Overview
ISO 7485:2000 specifies laboratory procedures for the determination of potassium (K) and sodium (Na) in animal feeding stuffs using flame-emission spectrometry. It defines two analytical approaches - a calibration (external standard) method and a standard addition method - and sets the limit of determination at 0.04 g/kg. The standard covers sample preparation (including ashing), reagent and standard solution preparation, instrument setup and measurement, calculation and reporting of results.
Key topics and requirements
- Scope and methods: Calibration method (use when matrix effects are absent) and standard addition method (use when matrix effects are unknown or suspected).
- Analytical principle: Flame-emission spectrometry at 766 nm for potassium and 589 nm for sodium (flame photometer or atomic absorption spectrometer in emission mode).
- Sample preparation: Incinerate test portions in a muffle furnace at ~550 °C, dissolve residues with hydrochloric acid, re-dissolve and dilute to a defined volume; separate procedures for samples with/without organic matter.
- Reagents and standards: Detailed recipes for K and Na stock/intermediate/calibration solutions, ionization/release buffer (cesium chloride and aluminium nitrate), and use of certified reference materials (CRMs) to validate performance (examples: IAEA and NIST CRMs).
- Instrumental settings and calibration: Prepare calibration solutions across a defined concentration range, adjust flame and burner, correct test emissions for blank emission, construct calibration curve or standard-addition graph.
- Quality control and precision: Analysis of CRMs is required for control; the standard includes interlaboratory-derived repeatability and reproducibility limits and references ISO 5725 for precision assessment.
- Reporting: Specify sample ID, sampling method, method variant used, any deviations or incidents, and the reported K and Na contents (rounded per provided rules).
Applications and users
ISO 7485:2000 is intended for:
- Feed testing laboratories performing routine quality control of animal feeds and feed ingredients.
- Regulatory and compliance labs verifying nutrient and mineral content of commercial feeds.
- Research laboratories studying mineral balances in feed formulations and animal nutrition.
Practical applications include verifying label claims, monitoring raw-material composition (maize, soybean meal, alfalfa, mixed feeds), and ensuring feed safety and nutritional adequacy.
Related standards
- ISO 6498:1998 - Preparation of test samples (normative reference).
- ISO 6497 - Recommended sampling methods for feeding stuffs (recommended).
- ISO 5725 - Precision of measurement methods (interlaboratory precision evaluation).
Keywords: ISO 7485, animal feeding stuffs, potassium analysis, sodium analysis, flame-emission spectrometry, flame photometer, standard addition method, calibration curve, feed testing, limit of determination.
Open preview (PDF)Animal feeding stuffs — Determination of potassium and sodium contents — Methods using flame-emission spectrometry