Overview
ISO 21422:2018 - "Milk, milk products, infant formula and adult nutritionals - Determination of chloride - Potentiometric titration method" specifies a validated analytical procedure for measuring chloride in milk and related products using potentiometric titration with silver nitrate (AgNO3). The method applies to powders, cheeses, butter, ready‑to‑feed (RTF) infant formula and adult nutritionals with an analytical range of 0.35 mg Cl/100 g to 711.6 mg Cl/100 g. The standard is published jointly by ISO and IDF and is equivalent to AOAC Official Method 2016.03.
Key topics and requirements
- Principle: Extract chloride from the sample (warm water extraction or direct analysis of RTF products); optionally precipitate proteins; titrate chloride ions with standardized AgNO3 potentiometrically using a combined silver electrode to detect the end point.
- Analytical range: 0.35–711.6 mg chloride per 100 g product (or RTF product).
- Reagents: Purified water, AgNO3 standardized titrant (0.1 mol/L; optional 0.025 mol/L), NaCl standard solutions, Carrez reagents (potassium ferrocyanide and zinc acetate) for protein precipitation, nitric acid, potassium nitrate, acetone, and defoaming agent.
- Apparatus: Precision balances, centrifuge (≥12 000 g), volumetric glassware, pH/mV meter, combined silver electrode, and an automatic titrator or motorized burette with autosampler compatibility.
- Sample preparation & extraction: Clause‑based procedures for powders, cheeses, butter and liquid products; includes optional protein precipitation and extraction steps to suit matrix type.
- Quality control: Includes system suitability tests, blank determinations, end‑point determination guidance (Annex A) and precision data (repeatability and reproducibility in Clause 13 and Annex B).
- Calculations & reporting: Defined formulas and reporting requirements for expressing chloride content in product units.
Applications
- Routine quality control and specification testing in dairy processing plants.
- Regulatory and food safety laboratories performing compliance testing for infant formula, adult nutritionals and dairy products.
- Research and method validation laboratories comparing chloride levels across product formulations, batches, or storage conditions.
- Use cases include monitoring salt content, tracking electrolyte balance in nutritionals, and verifying label claims.
Who should use this standard
- Dairy industry QC/QA teams
- Accredited testing laboratories
- Food safety authorities and regulators
- Manufacturers of infant formula and adult nutritionals
- Analytical chemists working with milk matrices
Related standards
- AOAC Official Method 2016.03 (equivalent method)
- ISO/IDF joint analytical publications for milk and milk products
ISO 21422:2018 provides a robust, traceable approach to chloride determination in complex dairy matrices, supporting reliable compliance testing and quality assurance across the dairy and nutrition sectors.
Keywords: ISO 21422, chloride determination, potentiometric titration, AgNO3 titration, milk products, infant formula, adult nutritionals, Carrez reagents, dairy quality control.