Potentiometric titration of calcium and magnesium in dairy products

Significance of the topic

Determination of calcium and magnesium in dairy products is crucial for ensuring nutritional quality, meeting regulatory requirements and controlling production processes. Potentiometric titration offers a rapid, cost-effective and accurate approach suited to routine laboratory analysis.

Objectives and overview

This study presents a streamlined potentiometric titration method using EGTA and EDTA as titrants and a copper ion-selective electrode as indicator. The approach enables separate quantification of calcium or combined calcium and magnesium without extensive sample pretreatment for liquid dairy matrices.

Methodology and instrumentation

Liquid samples such as milk and yogurt are diluted, whereas cheese is acidified, heated, and neutralized to release bound calcium. The sample is buffered at pH 10 and spiked with a copper complex indicator (CuEGTA or CuEDTA). Titration is performed under MET U mode with the following parameters:

• Titrant: 0.1 mol/L EGTA for calcium or 0.1 mol/L EDTA for calcium plus magnesium
• Buffer: 1 mol/L NH4Cl/25% NH3 at pH 10
• Stirring rate: 8; signal drift: 50 mV/min; volume increment: 0.1 mL
• Equivalence point recognized at 30 mV change

Instrumentation

• Automated titrator with MET mode
• 20 mL buret
• Magnetic stirrer
• Copper ion-selective electrode (Cu ISE) and reference electrode

Main results and discussion

Typical titration curves display sharp potential jumps at the equivalence point. Calcium in liquid products is fully accessible to EGTA, while cheese requires pretreatment. The method yields reproducible results with low titrant consumption and clear separation of endpoints for calcium and magnesium.

Benefits and practical applications

• Rapid analysis for routine quality control in dairy industry
• Minimal sample preparation for milk, yogurt and brine solutions
• Capability to distinguish calcium alone or combined calcium/magnesium content
• Use of copper ISE avoids interference from bound calcium species

Future trends and potential applications

Integration of this protocol into fully automated platforms may increase throughput. Expanding the method to other food matrices and exploring thermometric detection modes could further enhance versatility.

Conclusion

The described potentiometric titration offers a robust, efficient and accurate solution for calcium and magnesium analysis in dairy products, supporting quality assurance and regulatory compliance.

References

• Metrohm Application Bulletin 101: Complexometric titrations with the Cu ISE