Overview
ISO 15648:2004 / IDF 179:2004 specifies a standardized potentiometric method for determining the salt content of butter. It applies to all types of butter containing more than 0.1% (mass fraction) salt. The method measures chloride ions in a water suspension of the sample by potentiometric titration with a standardized silver nitrate solution and reports salt as NaCl (percent by mass).
Key topics and technical requirements
- Scope: Intended for butter with >0.1% salt; lower-salt samples give higher relative uncertainty.
- Principle: Chloride ions are titrated potentiometrically using AgNO3; endpoint detected by maximum potential difference between successive equal additions.
- Reagents:
- Standard volumetric silver nitrate solution, c(AgNO3) ≈ 0.08–0.12 mol·L⁻¹, standardized against dried NaCl.
- Nitric acid (~4 mol·L⁻¹) may be added (2–3 mL) for difficult titrations.
- Use distilled/demineralized, chloride-free water.
- Apparatus: potentiometer with a chloride-sensing measuring electrode (e.g., silver) and a reference electrode, burette or automatic plunger burette (protected from light), analytical balance (1 mg), stirrer and suitable vessels.
- Sample preparation: Homogenize if needed (warming below 30 °C), cool, then weigh 2–4 g test portion (record to 0.1 mg).
- Procedure: Dissolve in boiling (or cold then heated) water, cool below 55 °C, titrate potentiometrically with AgNO3 while stirring. Run a reagent blank.
- Calculation & reporting: Salt content is calculated from the difference between sample and blank titrant volumes, AgNO3 concentration, the conversion factor (equivalent Cl → NaCl), and sample mass. Results are expressed to two decimal places.
- Precision: Interlaboratory data give a repeatability limit r ≈ 0.05% and reproducibility limit R ≈ 0.08% (absolute differences).
Applications and users
This standard is used for:
- Quality control in dairy processing and butter manufacturing
- Regulatory compliance testing and labeling verification
- Routine laboratory analysis in food chemistry and dairy testing labs
- Research on salt distribution in dairy products
Typical users: analytical chemists, QA/QC managers in dairy plants, third‑party testing laboratories, national food control authorities and standardization bodies.
Related standards
- ISO 707 - guidance on sampling of milk and milk products (sampling is not part of ISO 15648)
- ISO 5725-1 / ISO 5725-2 - precision (trueness and precision) of measurement methods (used for interlaboratory statistics)
Keywords: ISO 15648:2004, butter salt content, potentiometric method, chloride titration, silver nitrate titration, dairy quality control, IDF 179.