Conductivity, pH value, alkalinity, and hardness in tap water

Importance of the Topic

Tap water analysis is fundamental for ensuring public health, process control, and regulatory compliance. Key parameters such as conductivity, pH, alkalinity, and hardness serve as primary indicators of water quality. Automated, multi-parametric workflows reduce manual errors and increase laboratory throughput.

Study Objectives and Overview

This application note presents a fully automated system capable of measuring conductivity, pH, alkalinity, and calcium/magnesium hardness in a single analysis. The platform integrates standard methods (ISO, EN, ASTM, EPA) and automates sample transfer, calibration, and titrant determination to enhance reproducibility and efficiency.

Methodology and Instrumentation

The workflow utilizes an 815 Robotic USB Sample Processor XL to transfer defined sample volumes into an external titration vessel. Analytical steps include:

• Conductivity measurement in the sample beaker using a five-ring conductivity cell with integrated temperature sensor.
• pH determination with an intelligent combined pH electrode and temperature sensor.
• Alkalinity titration using standardized hydrochloric acid.
• pH adjustment with TRIS buffer and complexometric titration with EDTA for hardness assessment.
• Automated cleaning of the titration vessel and sensors between samples.

Used Instrumentation

• 815 Robotic USB Sample Processor XL: Automated sample handling with membrane pumps and robotic arm.
• 856 Conductivity Module with five-ring cell (c = 0.7 cm⁻¹) and Pt1000 temperature sensor.
• 905 Titrando titrator compatible with Dosino dosing systems and intelligent electrodes.
• iAquatrode Plus combined pH electrode with integrated memory and temperature sensor.
• Polymer membrane calcium-selective electrode for hardness determination.

Main Results and Discussion

Analysis of ten tap water samples yielded highly reproducible data with a total cycle time under 15 minutes:

• Conductivity: 525 µS/cm (rel. SD 0.8%)
• pH value: 7.81 (rel. SD 0.5%)
• Alkalinity: 5.8 mmol/L (rel. SD 0.1%)
• Calcium: 88.8 mg/L (rel. SD 0.2%)
• Magnesium: 19.9 mg/L (rel. SD 1.4%)
• Total hardness: 3.9 mmol/L (rel. SD 0.4%)

The results confirm the system’s precision and suitability for routine water quality monitoring.

Benefits and Practical Applications

• Minimized manual handling and reduced operator workload.
• Compliance with multiple international standards in a single run.
• High reproducibility supports QA/QC and regulatory reporting.
• Ideal for water treatment plants, environmental testing, and industrial quality control.

Future Trends and Applications

Future developments may include integration of additional sensors for trace metals and organics, inline monitoring for process control, and advanced data analytics for real-time water quality assessment. Miniaturization and remote operation could enable decentralized and continuous environmental surveillance.

Conclusion

The described automated platform delivers rapid, accurate, and reproducible measurements of conductivity, pH, alkalinity, and hardness in tap water. Its high level of automation increases throughput and reliability, making it a valuable tool for diverse water quality applications.

References

Standard methods referenced include ISO 7888, EN 27888, ASTM D1125, EPA 120.1; EN ISO 10523, ASTM D1293, EPA 150.1; EN ISO 9963, ASTM D1067, EPA 310.1; ISO 6059, ASTM D1126, EPA 130.2.