Simultaneous determination of calcium, magnesium, and alkalinity by complexometric titration with potentiometric or photometric indication in water and beverage samples

Importance of the Topic

Accurate measurement of calcium, magnesium, and alkalinity in water and beverages is essential for quality control, regulatory compliance, and treatment optimization. Hardness parameters influence industrial processes, consumer health, and taste profiles in beverages.

Objectives and Study Overview

The study outlines a unified approach for determining alkalinity, calcium, and magnesium levels in water and beverage samples. It compares potentiometric complexometric titration with EDTA and photometric titration using colorimetric indicators, providing method details, definitions of hardness types, and calculation formulas.

Methodology

Potentiometric procedure:

• Separate acid–base titration with HCl to determine alkalinity.
• Complexometric titration with EDTA after masking and pH adjustment to detect Ca2+ and Mg2+ endpoints on a combined electrode.
• Calculation of permanent hardness by subtracting alkalinity from total hardness.

Photometric procedure:

• Total hardness by titration with EDTA and Eriochrome Black T at 610 nm.
• Calcium hardness by titration with EDTA and calconcarboxylic acid at 610 nm.
• Difference between total and calcium hardness yields magnesium hardness.

Used Instrumentation

• Titrator with DET mode for potentiometry and MET mode for photometry.
• 20 mL burette, magnetic stirrer.
• Combined Ca2+ selective electrode (Ecotrode Plus, Ecotrode gel).
• Optrode photometric sensor (610 nm).

Main Findings and Discussion

Potentiometric titrations provided clear dual equivalence points for Ca2+ and Mg2+, with example tap water results of ~109.8 mg/L Ca and ~21.9 mg/L Mg. Photometric titrations delivered reliable total and calcium hardness values in both water and ashed beverage samples. The methods accommodate a wide hardness range and various sample matrices, with precision ensured by titer calibration and endpoint recognition algorithms.

Benefits and Practical Applications

• Fully automated workflow reduces manual steps and improves throughput.
• Applicable to municipal and industrial water analysis, fruit juices, wines, and other beverages.
• Supports regulatory standards and customer specifications for hardness and alkalinity.

Future Trends and Applications

Integration of advanced sensing technologies for inline monitoring, miniaturized titration systems for field use, and AI-driven endpoint detection are expected to enhance speed, data quality, and adaptability to complex matrices.

Conclusion

The combined potentiometric and photometric EDTA titration methods offer robust, precise, and versatile solutions for simultaneous determination of alkalinity, calcium, and magnesium in water and beverages, streamlining analytical workflows in laboratories.

Reference

• DIN 38406-3: Complexometric determination of calcium and magnesium.
• EN ISO 9963-1: Determination of total and composite alkalinity.
• EPA 130.2: Total hardness by EDTA titrimetry.
• EPA 310.1: Alkalinity titration.
• ASTM D1126: Hardness in water.
• Christiansen T.F., Busch J.E., Krogh S.C.: Anal. Chem. 70 (1976) 1051–1056.