Automated potentiometric titration of aluminum and magnesium in the same solution

Significance of the topic

Determination of aluminum and magnesium is critical in various industries including pharmaceuticals, environmental monitoring, and metals processing. Automated potentiometric titration enhances analytical efficiency, improves reproducibility, and reduces operator workload.

Objective and overview

This study presents a unified workflow for the sequential titration of aluminum and magnesium in the same sample matrix. The method employs 1,2-diaminocyclohexanetetraacetic acid (DCTA) for complexation and back-titration of excess ligand with copper(II) sulfate, using a copper ion-selective electrode (Cu ISE) for endpoint detection.

Methodology and instrumentation

The analytical procedure consists of two back-titrations under distinct pH conditions:

• Aluminum determination in acidic medium: DCTA is added to the sample, allowed to react, and excess DCTA is back-titrated with CuSO4.
• Magnesium determination in alkaline medium: Additional DCTA and ammonia buffer are added, and the remaining ligand is back-titrated with CuSO4.

The titrations are performed on an automated potentiometric titrator in MET mode, equipped with dual copper ISE and reference electrodes. Reagents include CuSO4·5H2O, DCTA, sodium acetate buffer, ammonia, and standardized titrants.

Main results and discussion

Distinct equivalence points for aluminum and magnesium were obtained, as illustrated by characteristic titration curves. The method demonstrates reliable endpoint detection, minimal sample preparation, and high reproducibility. No significant interferences were observed in mixed-element matrices.

Benefits and practical applications

• Simultaneous analysis of Al and Mg without the need for separate aliquots.
• Fully automated sequence reduces manual handling and potential for error.
• Rapid throughput suitable for routine quality control laboratories.

Future trends and opportunities

Potential developments include integration with flow injection analysis, miniaturized electrochemical cells, and expansion to additional metal ions using selective ligands. Software enhancements could improve automated data evaluation and method validation.

Conclusion

The described automated potentiometric titration protocol provides a robust and efficient approach for simultaneous aluminum and magnesium analysis. Its simplicity, accuracy, and adaptability make it well-suited for high-throughput industrial and research laboratories.

Instrumentation used

• Automated MET-mode potentiometric titrator
• 10 mL burets (two channels)
• Copper ion-selective electrode and reference electrode
• Sample changer for unattended operation