Determination of Calcium and Magnesium in Milk

Significance of the Topic

Accurate determination of calcium and magnesium levels in milk is vital for nutritional labeling, quality control and regulatory compliance in the dairy industry. These minerals support bone health, metabolic functions and overall food quality. A robust, precise and automated titrimetric approach ensures reliable monitoring of milk composition across different product types.

Study Objectives and Overview

This application note describes a thermometric titration method for simultaneous quantification of calcium and magnesium in various milk samples. The study aims to optimize sample preparation, establish clear endpoints for each ion, and demonstrate method performance on full cream, low fat and skim milk enriched with milk solids.

Methodology

Sample Preparation and Reagents

• Milk coagulation: 100 mL of milk is mixed with 10 mL of 25% trichloroacetic acid and stirred for protein precipitation.
• Serum separation: Clarified serum is obtained by filtration or centrifugation.
• Complexing agent: Acetylacetone is added to adjust the stability constants of the metal–EDTA complexes for sharper endpoints.
• Titrant and buffer: A 1 mol/L tetrasodium EDTA solution is used as titrant. An ammonia/ammonium chloride buffer maintains pH around 10 for optimal chelation.

Procedure

• Transfer 50 mL of the clarified serum to the titration vessel (equivalent to 45.45 mL original milk).
• Add 800 µL acetylacetone and 5 mL buffer automatically by Dosino.
• Perform thermometric titration at a delivery rate of 4 mL/min, stirring at setting 15, with a 10-second pre-titration delay.
• Detect exothermic calcium endpoint at a set reference of –15 and endothermic magnesium endpoint at +5.

Used Instrumentation

• Thermometric titrator equipped with a Dosino dosing module
• Magnetic stirrer with 80 mm stir bar
• Temperature sensor for real-time thermometric endpoint detection
• Whatman no. 4 filter paper or laboratory centrifuge for serum clarification

Main Results and Discussion

The method was applied to three milk types. Measured calcium values were 125.9, 147.0 and 209.7 mg/100 mL for full cream, low fat and skim with added solids, respectively, closely matching label claims of 117, 145 and 175 mg/100 mL. Magnesium results of 13.2, 14.8 and 14.5 mg/100 mL also aligned with expected levels. Blank corrections for calcium and magnesium endpoints were determined by linear regression of titrant consumption versus sample volume. Thermometric plots revealed distinct exothermic and endothermic peaks corresponding to each metal, demonstrating clear separation of endpoints.

Benefits and Practical Applications of the Method

The proposed thermometric titration offers:

• High automation and reproducibility, reducing operator error
• Rapid analysis with clear dual endpoints for calcium and magnesium
• Minimal sample manipulation through simple acid precipitation and filtration
• Adaptability to routine quality control in dairy processing and regulatory testing

Future Trends and Potential Applications

Advances may include integration of continuous flow sample preparation for high-throughput dairies, coupling with data analytics for process control, and extension to other food matrices. Development of miniaturized thermometric sensors could enable inline monitoring of mineral content in real time.

Conclusion

This thermometric titration method provides a reliable, automated approach for simultaneous quantification of calcium and magnesium in milk. Its precision, speed and minimal sample preparation make it well suited to dairy quality control and regulatory compliance.