Water analysis

Importance of the Topic

Water quality analysis is essential for safeguarding public health and ensuring environmental compliance. Precise measurement of pH, alkalinity, and hardness underpins drinking water treatment, distribution monitoring, and regulatory control.

Objectives and Overview of the Study

This work evaluates analytical approaches for assessing pH value, carbonate alkalinity, and total hardness in low-ionic strength water. It compares the performance of a novel Aquatrode Plus electrode against a conventional pH glass electrode and demonstrates the use of a calcium ion-selective electrode (Ca ISE) for routine hardness determination.

Methodology and Instrumentation

pH measurements were conducted potentiometrically in poorly buffered drinking water, calibrated with standard buffers at pH 4.005, 6.863, and 9.184. Carbonate alkalinity was determined according to EN ISO 9963-2 via SET titration with 0.05 mol/L HCl to pH 5.4. Total hardness was assessed by potentiometric titration using a polymer-membrane Ca ISE capable of detecting Ca²⁺ and Mg²⁺ simultaneously.

Instrumentation Used

• Aquatrode Plus combined pH electrode with fixed ground-joint diaphragm and gel inner electrolyte for rapid response and stability.
• Standard pH glass electrode with ceramic pin diaphragm for comparison.
• Polymer membrane calcium ISE with measuring range 5×10⁻⁷ to 1 mol/L and high selectivity over Mg²⁺ and H⁺.

Key Results and Discussion

• The Aquatrode Plus delivered accurate pH readings (matching reference value ~9.98) rapidly and was insensitive to stirring rate, whereas the standard electrode showed slower response and pH drift with mixing speed.
• Alkalinity titrations met ISO criteria when employing electrodes with fast membrane response.
• The Ca ISE reliably quantified calcium and magnesium at concentrations down to 0.01 mmol/L, even at Ca/Mg ratios up to 10:1, though Mg precision improved with matrix spiking.

Benefits and Practical Applications of the Method

• Enhanced pH measurement in low-conductivity waters supports optimized treatment processes.
• Reliable alkalinity determination facilitates corrosion control and compliance monitoring.
• Ion-selective hardness measurement offers a cost-effective tool for routine water quality surveillance.

Future Trends and Potential Applications

• Integration of smart sensors for continuous, automated on-line water monitoring.
• Development of multifunctional probes combining pH, conductivity, and specific ion detection.
• Advancements in membrane materials to further lower detection limits and enhance selectivity.

Conclusion

Modern electrode designs such as the Aquatrode Plus and specialized ion-selective sensors significantly improve the speed, accuracy, and reliability of fundamental water quality determinations.

References

EN ISO 9963-2 (1996-02)