Photometric determination of sulfate in aqueous solutions

Significance of the Topic

The reliable determination of sulfate in aqueous solutions is essential in environmental monitoring, industrial process control and quality assurance of water and wastewater. Sulfate concentration influences corrosion, scale formation, and regulatory compliance, making rapid and accurate methods indispensable for laboratories and industrial settings.

Objectives and Overview of the Application Note

This Application Note T–77 outlines a photometric back-titration method for sulfate based on precipitation with barium chloride followed by titration of excess barium ion with EDTA, using an optical sensor at 520 nm. The protocol aims to deliver precise, reproducible sulfate measurements in a straightforward automated workflow.

Methodology and Instrumentation

The approach involves acidifying the sample, precipitating sulfate as barium sulfate, and then determining excess Ba2+ by titration with Na2EDTA (0.025 mol/L) under photometric detection. No complex sample preparation is required beyond acid addition and dilution.

• Automated Titrator: 907 Titrando with DET mode
• Dosing Units: Dosino modules (2, 10, 50 mL)
• Optrode Sensor: Photometric detection at 520 nm
• Stirring and Robotic Handling: 802 rod stirrer and 815 USB SP robot

Main Results and Discussion

Replicate analyses (n=6) yielded an average sulfate concentration of 0.0516 mol/L with a standard deviation of 0.0002 mol/L, demonstrating high precision. The optical endpoint detection at 520 nm provided clear signal changes at the completion of back-titration, supporting reliable endpoint recognition.

Benefits and Practical Applications

This method offers:

• High precision and low method drift
• Minimal sample preparation and rapid analysis time
• Full automation capability for high throughput
• Applicability to various aqueous matrices in QA/QC and research laboratories

Future Trends and Potential Applications

Advancements may include miniaturized optical sensors, integration with flow injection analysis, and adaptation for field-deployable platforms. Coupling with data analytics could further enhance throughput and real-time monitoring in environmental and process control applications.

Conclusion

The photometric back-titration method using an Optrode at 520 nm provides a robust, precise and automated solution for sulfate determination in aqueous samples. Its simplicity and reproducibility make it suitable for routine laboratory use and industrial quality control.

Reference

• Titration Application Note T–77, Version 1