ISO 9874:2006 (IDF 42:2006) - Milk - Determination of total phosphorus content
Overview
ISO 9874:2006 specifies a validated laboratory method for determining the total phosphorus content of milk using molecular absorption spectrometry. The method converts phosphorus into a coloured molybdenum‑blue complex and measures absorbance at 820 nm. It covers sample preparation (wet digestion or dry ashing), reagent and apparatus requirements, calibration, calculation, precision and reporting. This standard is published jointly by ISO and the International Dairy Federation (IDF 42).
Key topics and technical requirements
- Scope: Quantitative determination of total phosphorus in milk expressed as a mass fraction (percent).
- Analytical principle: Wet digestion with sulfuric acid and hydrogen peroxide or dry ashing, formation of molybdenum blue (molybdate + ascorbic acid) and spectrophotometric measurement at 820 nm using 10 mm cells.
- Reagents: Analytical‑grade sulfuric and hydrochloric acids, hydrogen peroxide, sodium molybdate, fresh ascorbic acid, and prepared KH2PO4 standard solutions (e.g., 100 mg/L and 10 mg/L reference solutions described).
- Sample handling: Bring samples to 20 °C ± 2 °C; if fat is not well dispersed, warm to 40 °C then cool before analysis.
- Apparatus: Standard laboratory glassware (ISO 648, ISO 1042, ISO 4788), molecular absorption spectrometer (820 nm), digestion flasks or platinum/silica dishes, electric furnace (500–550 °C) for ashing.
- Calibration & quality control: Multi‑point calibration graph using aliquots of the 10 mg/L standard; concurrent blank test; spectrometric readings performed within 1 hour of colour development.
- Precision: Repeatability limit 0.005% (mass fraction); reproducibility limit 0.016% (mass fraction). Results reported to three decimal places.
- Calculation: Convert measured net absorbance to micrograms of phosphorus using the calibration curve; apply the standard formulae for wet digestion or dry ashing sample mass.
Practical applications and users
- Laboratories performing dairy product analysis, routine quality control and compositional testing.
- Regulatory and food safety authorities verifying compliance with labeling and nutritional claims.
- Research labs studying milk composition, phosphorus content in feed/processing studies, or nutrient balance.
- Dairy processors monitoring process control (e.g., fortification, standardization) and ingredient suppliers verifying specifications.
Keywords: ISO 9874:2006, IDF 42, total phosphorus, milk analysis, molecular absorption spectrometry, molybdenum blue, wet digestion, dry ashing, spectrophotometry.
Related standards
This standard provides a robust, reproducible procedure for phosphorus determination in milk, suitable for accredited dairy testing laboratories and quality management systems.
