Overview
ISO 6227:1982 specifies a general potentiometric method for determination of chloride ions in solutions prepared from chemical products for industrial use. The technique is a potentiometric titration of chloride (Cl−) with standard volumetric silver nitrate (AgNO3) in an acid medium and in the presence of acetone, using a silver electrode or a chloride / silver ion‑selective electrode as the measuring electrode and a calomel or mercury(I) sulphate electrode as reference. Applicable concentration range: 1 to 1 500 mg/L chloride.
Key topics and technical requirements
- Titration principle: Potentiometric titration of Cl− with AgNO3; end‑point detected by electrode potential changes.
- Electrodes & instrumentation:
- Measuring electrode: silver electrode or chloride/silver ion‑selective electrode.
- Reference electrode: calomel or mercury(I) sulphate electrode.
- Potentiometer with sensitivity ≥ 2 mV and ±500 mV range.
- Bridge with saturated potassium nitrate when calomel electrode is used.
- Reagents and standard solutions:
- Silver nitrate standard solutions (examples: 0.1, 0.01, 0.004 mol/L prepared from a 0.1 mol/L stock).
- Standard potassium chloride (KCl) reference solutions for standardization.
- Nitric acid (~68% w/w) and acetone (acetone : aqueous solution ratio recommended ~80:10 V/V, minimum 50:50).
- Procedure essentials:
- Carry out a reagent blank and standardize selected AgNO3 by titration against KCl in the blank matrix.
- Use controlled small‑volume increments (0.05–0.2 mL) of AgNO3 during titration; record potential vs volume and compute endpoint from potential increments.
- Calculation formulas provided for c(AgNO3), blank correction, and mass of chloride expressed as chlorine (constant 0.03545 g Cl per mL of 1 mol/L AgNO3).
- Interferences & sample preparation:
- Annex C lists interferences (bromide, iodide, cyanides, sulphides, thiocyanates, ammonium and Fe(III)) and suggested eliminations.
- Annex B describes mineralization methods for converting organic‑bound chlorine to chloride (combustion, fusion, hydrolysis) before analysis.
Applications and users
ISO 6227 is intended for quality control and analytical laboratories handling industrial chemicals where accurate chloride determination is required, including:
- Manufacturers of chemical products performing batch release testing.
- Contract and in‑house analytical labs validating chloride content in raw materials, intermediates and finished products.
- Laboratories preparing samples from organic matrices (using annex B mineralization) to determine total chlorine as chloride.
- Users implementing potentiometric titration with ion‑selective electrodes for automated or manual chloride analysis.
Related standards
- Developed by ISO/TC 47 (Chemistry). Specific product standards referenced in ISO 6227 define sample preparation and any product‑specific modifications. Alternative chloride determination methods (e.g., ion chromatography, argentometric titration) may be used where specified by product standards.
Keywords: ISO 6227, chloride determination, potentiometric titration, silver nitrate, ion‑selective electrode, industrial chemicals, chloride ions, standardization.
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