Potentiometric titration of chloride and bromide in the presence of each other

Importance of the Topic

Accurate measurement of chloride and bromide ions is essential in water quality monitoring, chemical production, pharmaceutical analysis and industrial process control. Potentiometric titration offers a cost-effective and reliable approach for simultaneous or selective quantification of these halides, even in complex matrices.

Objectives and Overview of the Study

This application bulletin presents two potentiometric titration protocols for samples containing both chloride and bromide ions. Method A addresses simultaneous determination when both ions are present in near-equal concentrations. Method B enables selective measurement of bromide in the presence of a large excess of chloride, overcoming interferences observed in direct silver titration.

Methodology

Method A – Simultaneous Titration

• Sample volume: 50 mL
• Reagents: 0.1 M AgNO₃ titrant, 2 M HNO₃, barium acetate
• Procedure: Acidify sample, add barium acetate to suppress precipitation effects, titrate with Ag⁺ and record two endpoints corresponding to Br⁻ and Cl⁻.

Method B – Selective Bromide Determination

• Sample volume: 25 mL, neutralized and containing up to 12 mg Br⁻
• Reagents: 1 M NaClO, 25% HCOONa, KI, 0.1 M Na₂S₂O₃ titrant, H₂SO₄, ammonium molybdate catalyst, NaCl, NaH₂PO₄
• Procedure: Oxidize bromide to bromate, convert to iodine using iodide, acidify and catalyze, then back-titrate released I₂ with thiosulfate using a platinum electrode.

Instrumentation

Both methods employ Metrohm potentiometric titrators (models 702, 716, 736, 751, 785 or 796 with Dosino units), magnetic stirrer, exchange units, silver Titrode with Ag₂S coating and platinum Titrode. Endpoint detection and dosing parameters are optimized for minimal drift and clear equivalence point recognition.

Main Results and Discussion

Method A yields two distinct equivalence points. Calculations convert reagent consumption to mg/L of Br and Cl. Relative error tests over molar ratios from 1∶10 to 10∶1 show that addition of barium acetate significantly reduces error, improving accuracy for both ions. Method B achieves reliable bromide quantification in chloride excess, with a detection limit driven by thiosulfate titration sensitivity.

Benefits and Practical Applications

These titration protocols offer:

• High selectivity and precision in mixed halide samples
• Simple sample preparation and straightforward calculation
• Compatibility with routine laboratory titrators for QA/QC tasks
• Minimal reagent consumption and waste generation

Future Trends and Potential Applications

Advances in electrode materials, automated dosing algorithms and integration with flow-injection systems will enhance speed and reproducibility. Coupling potentiometric titration with data analytics and machine learning may further improve endpoint detection and method robustness across diverse matrices.

Conclusion

The two potentiometric titration methods described enable accurate determination of chloride and bromide under varying concentration ratios. Method A provides simultaneous quantification when halides are present in similar amounts, while Method B extends capability to trace bromide analysis in high chloride backgrounds. Both approaches are well suited for routine industrial and environmental applications.

References

• Kolthoff W and Belcher D Volumetric Analysis Volumes II and III Interscience Publishers New York London