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

Importance of the topic

Complexometric titration with potentiometric or photometric indication enables simultaneous quantification of alkalinity, calcium, and magnesium levels critical for water quality monitoring and beverage analysis. Accurate hardness and alkalinity data support regulatory compliance, process control, and resource management.

Objectives and Overview

The method aims to streamline the determination of water and beverage hardness by employing EDTA titration with either potentiometric or photometric detection. It covers separate acid–base titration for alkalinity, followed by complexometric titration for calcium and magnesium, and provides an alternative photometric protocol according to established standards.

Methodology and Instrumentation

• Potentiometric approach: Sequential titration of alkalinity with HCl (0.1 M), then calcium and magnesium with EDTA (0.05 M), using a combined pH/Ca²⁺ selective electrode for endpoint detection.
• Photometric approach: Titration of total hardness and calcium hardness with EDTA (0.1 M) using optical detection at 610 nm with Eriochrome Black T and calconcarboxylic acid indicators.
• Sample preparation: Direct titration of water samples; ashing of beverage residues at 600 °C for total metal recovery.
• Key reagents: Standardized HCl and EDTA solutions, TRIS buffer, acetylacetone auxiliary solution, Eriochrome Black T and calconcarboxylic acid indicators.

Main Results and Discussion

Application of the potentiometric protocol yielded typical tap water values of 109.8 mg/L Ca²⁺ and 21.9 mg/L Mg²⁺, with clear dual endpoints. Photometric titrations provided reliable total hardness and calcium hardness determinations, enabling indirect calculation of magnesium. The procedure demonstrated high reproducibility, minimal interference after auxiliary complexation of Fe³⁺ and Al³⁺, and adaptability across sample matrices.

Benefits and Practical Applications

• Automatable workflows with DET and MET modes for unattended sample series.
• Reduced analysis time by combining multiple analytes in one run.
• Robust performance in diverse matrices including drinking water, juices, and wines.
• Compliance with international standards (DIN, ISO, EPA, ASTM).

Future Trends and Opportunities

Advances may include integration of real-time sensors for inline monitoring, miniaturized titration cells, and coupling with data management systems for enhanced process analytics. Novel indicator chemistries and multimodal detection could further expand selectivity and sensitivity.

Conclusion

The described EDTA-based titration methods offer reliable, versatile solutions for simultaneous determination of alkalinity and hardness parameters in water and beverage samples. Their automation potential and conformity to standard methods make them valuable for labs focused on quality control and environmental monitoring.

Used Instrumentation

• Titrator with DET (potentiometric) and MET (photometric) modes
• 20 mL burette, magnetic stirrer
• Combined Ca²⁺ selective electrode (e.g. Ecotrode Plus) and optical electrode (Optrode 6.1115.000)

Reference

• DIN 38406-3. German Standard Methods for the Examination of Water – Determination of Calcium and Magnesium.
• EN ISO 9963-1. Water Quality – Determination of Alkalinity.
• EPA Method 130.2. Total Hardness by EDTA Titrimetry.
• EPA Method 310.1. Alkalinity (pH Endpoint at 4.5).
• ASTM D1126. Standard Test Method for Hardness in Water.
• Christiansen, T.F., Busch, J.E., Krogh, S.C. (1976). Successive Potentiometric Titration of Calcium and Magnesium. Analytical Chemistry, 48(7), 1051–1056.
• Metrohm Application Bulletins AB-178, AB-206, AB-221.
• SCA Blue Book 43–44. Methods for Hardness and Alkalinity Determination.