Determination of calcium in cement by photometric titration of the solubilized product according to EN 196-2

Importance of the Topic

The accurate quantification of calcium in cement is critical for quality control, compliance with construction standards, and ensuring the performance of cement-based materials. Photometric titration provides a rapid, sensitive, and automatable approach to determine calcium levels following standardized digestion methods.

Aim and Study Overview

This application note describes a photometric titration procedure for calcium determination in cement according to the DIN EN 196-2 digestion protocol. After digestion, calcium is complexed with EDTA and the endpoint is detected photometrically using a chromogenic indicator at 610 nm.

Methodology and Instrumentation

The cement sample is digested per DIN EN 196-2 and an aliquot (10 mL) is adjusted to pH 12.5 with NaOH. A murexide indicator is added, and the solution is titrated with standardized Na2EDTA. The photometric endpoint is monitored at 610 nm, where the color shifts from pink to violet.

• Digestion: Acid digestion following DIN EN 196-2
• Titrant: 0.03 mol/L Na2EDTA (titered against Ca standard)
• Indicator: Murexide in NaCl matrix
• pH Adjustment: Saturated NaOH
• Endpoint Detection: Optrode sensor at 610 nm

Used Instrumentation

• 907 Titrando with 800 Dosino units
• 5 mL, 10 mL, 50 mL dosing units
• 802 Rod Stirrer, 815 Robotic USB sample processor
• Optrode photometric sensor (610 nm) with Ecotrode plus electrode

Key Results and Discussion

The method yields highly reproducible results: CaO 48.81 % ± 0.209 (n=6) and Ca 34.89 % ± 0.151 (n=6). The photometric detection at 610 nm ensures a clear color transition and precise equivalence point determination. Measurement drift and endpoint criteria are optimized for minimal noise and accurate titration curves.

Benefits and Practical Applications

• High precision and repeatability for cement quality control
• Automatable workflow with robotic sample handling
• Compliance with international standards (DIN EN 196-2)
• Rapid results suitable for routine laboratory and production monitoring

Future Trends and Potential Applications

Advances may include integration with inline process analytics for real-time monitoring, miniaturized sensors for on-site testing, and coupling with chemometric tools to broaden multi-element analysis in construction materials.

Conclusion

Photometric titration using EDTA and murexide at 610 nm provides a robust, standardized method for calcium determination in cement. The approach delivers reliable, traceable results and supports efficient laboratory workflows aligned with industry standards.

Reference

• Application Note T–79: Photometric Determination of Calcium in Cement by EDTA Titration (DIN EN 196-2)