Automated determination of Calcium and Magnesium in milk with 859 Titrotherm and 814 USB Sample Processor

Importance of the Topic

Accurate quantification of calcium and magnesium in milk is vital for nutritional labeling, quality control in dairy production and ensuring regulatory compliance. Thermometric titration provides a rapid and reliable alternative to classical methods, reducing manual labor while delivering precise results across a variety of milk products.

Objectives and Study Overview

• Develop an automated thermometric titration workflow for simultaneous determination of calcium and magnesium in milk.
• Validate the method across full cream, low fat and skim milk products.
• Establish calibration, blank correction and statistical reproducibility using standard reagents.

Methodology and Instrumentation

The method relies on trichloroacetic acid coagulation to precipitate proteins and fats, followed by separation of the clear serum. Acetylacetone is added to sharpen the calcium and magnesium titration endpoints, and an ammonia/ammonium chloride buffer adjusts pH before titration. Thermometric detection monitors temperature changes during a constant addition rate of Na4EDTA titrant. Two distinct inflections are recorded: an exothermic peak for calcium and an endothermic peak for magnesium. Calibration curves are generated by regression of standard titrations, and method blanks are determined via linear intercepts to correct for matrix effects.

Used Instrumentation

• 859 Titrotherm thermometric titrator with dosing units (5 and 20 mL).
• 814 USB Sample Processor for automated sample handling.
• Dosino dosing modules for reagent and buffer delivery.
• Thermoprobe sensor and magnetic stirrer for temperature monitoring.
• Standard laboratory accessories including filtration and pipetting tools.

Main Results and Discussion

Calibration of a 1.0 mol/L Na4EDTA titrant yielded a slope of 1.003 with R2=1.00, demonstrating excellent linearity. Method blanks for calcium and magnesium were determined with high correlation (R2>0.999). Analysis of commercial milk samples showed calcium concentrations of 125.9±0.5 mg/100 mL in full cream, 147.0±0.4 mg/100 mL in low fat and 209.7±0.5 mg/100 mL in fortified skim milk. Magnesium values ranged from 13.2±0.4 to 14.8±0.6 mg/100 mL. Results closely matched nutritional label claims and exhibited good repeatability across multiple replicates.

Benefits and Practical Applications

• Fully automated titration minimizes operator intervention and error.
• Thermometric endpoints eliminate electrode maintenance and insulation requirements.
• High throughput supports routine quality control in dairy laboratories.
• Adaptable to different milk formulations, including fortified and low-fat variants.

Future Trends and Potential Applications

Integration with laboratory information management systems (LIMS) will streamline data handling and reporting. Extending thermometric titration to other food matrices and additional metal ions could enhance process control in diverse industries. Miniaturized titration platforms may enable point-of-need testing on production lines or in small laboratories.

Conclusion

The automated thermometric titration method using the 859 Titrotherm and 814 USB Sample Processor offers a robust, precise and efficient solution for calcium and magnesium analysis in milk, supporting modern dairy quality assurance workflows.