Determination of magnesium in cement by photometric titration of the solubilized product

Significance of the Topic

Precise determination of magnesium content in cement is essential for ensuring product quality, controlling setting properties, and maintaining compliance with industry standards.

Objectives and Overview

This study outlines a photometric titration method for quantifying magnesium in Portland cement. Following acid digestion, magnesium is complexed with EDTA and detected photometrically using an optical sensor at 610 nm while the endpoint is indicated by methylthymol blue.

Methodology and Instrumentation

• Sample Preparation and Digestion
  2.5075 g of cement mixed with 1.5 g NH4Cl, treated with concentrated HCl and HNO3 (1:1), and boiled for 40 minutes. The residue is dissolved in hot water, filtered, and diluted to 500 mL, adjusting pH to 10.0 with ammonia.
• Titration Procedure
  After adding 1 mL methylthymol blue indicator, the solution is titrated automatically with 0.1 mol/L EDTA at 610 nm. The endpoint color change from blue to brownish pink is detected photometrically. Parameters include MET U mode, 0.05 mL dosing increments, stirring speed 8, and a slope criterion of 0.9.
• Calculation
  Magnesium oxide content is calculated using titrant consumption and sample weight, applying the formula % MgO = (BP1 – C01) × C02 × C03 × C04 / C00 × 100.

Used Instrumentation

• 907 Titrando
• 800 Dosino with dosing units (2 mL, 5 mL, 10 mL, 50 mL)
• Optrode detector at 610 nm
• Rod stirrer and robotic USB sample handling
• Unitrode with Pt1000 electrode and standard cables

Main Results and Discussion

The method yields a magnesium oxide content of 1.08 ± 0.009% (n=3), equivalent to 0.33 ± 0.002 mg Mg per sample. Photometric endpoint detection provides precise and reproducible results with minimal operator intervention.

Benefits and Practical Applications

• High reproducibility and accuracy for cement quality control
• Automated titration reduces manual effort and potential errors
• Photometric detection enhances endpoint recognition in complex matrices

Future Trends and Opportunities

Advancements may include integration with inline process monitoring, multiwavelength detection for simultaneous analysis of other metal ions, and application to broader cement and construction material assays.

Conclusion

The described photometric titration method offers a robust, automated, and precise approach for magnesium determination in cement, supporting quality assurance and compliance with industry requirements.