The analysis of tap water plays an important role to assess the water quality or to identify its possible contamination. Parameters such as conductivity, pH value, alkalinity, and chloride content are routinely measured.

In this application note, a fully automated system is presented which allows the determination of several parameters according to various standards within one analysis. These include conductivity (ISO 7888, EN 27888, ASTM D1125, EPA 120.1), pH value (EN ISO 10523, ASTM D1293, EPA 150.1), alkalinity (EN ISO 9963, ASTM D1067, EPA 310.1), and chloride content (ISO 9297, ASTM D512, EPA 325.3). Additionally the system transfers the required volume of sample into an external titration vessel, further reducing manual sample preparation. Furthermore, all sensors can be calibrated automatically and the titer of each titrant can also be determined.

This high degree of automation minimizes errors and guarantees outstanding reproducibility by freeing up valuable time for operators.

The method is demonstrated for a tap water sample. No sample preparation is required as the system automatically transfers the defined sample volume to the external titration cell after conductivity measurement.

Example system: 815 Robotic USB Sample Processor XL with an external titration vessel, 905 Titrando and 856 Conductivity Module equipped with iAquatrode plus, iAg-Titrode, and 5-ring conductivity measuring cell for the analysis of tap water.
Figure 1. Example system: 815 Robotic USB Sample Processor XL with an external titration vessel, 905 Titrando and 856 Conductivity Module equipped with iAquatrode plus, iAg-Titrode, and 5-ring conductivity measuring cell for the analysis of tap water.

This analysis is carried out automatically on an 815 Robotic USB Sample Processor XL equipped with two external titration vessels. One is set up with an iAquatrode plus, and the second one is set up with an iAg-Titrode.

The samples are poured into beakers and placed onto the rack. The conductivity measurement is performed directly in the beaker using a 5-ring conductivity measuring cell with integrated temperature sensor. Afterwards, a sample aliquot is transferred into the first external titration vessel where the pH measurement and then the alkalinity titration (using standardized HCl solution) is performed. Then, a second aliquot is pipetted into the second titration vessel, where (after an acidification step) the chloride is titrated with standardized silver nitrate solution. Finally, the cleaning of both titration vessels and sensors is carried out automatically.

The pH electrode and the conductivity measuring cell are calibrated prior to the analysis.

The system enables reproducible results for all analyzed parameters. The overall analysis time for one sample is less than 15 minutes. All results are summarized in Table 1.

Table 1. Analyzed parameters for tap water (n = 10).
Parameter Mean SD(rel) in %
Conductivity 557.8 µS/cm 2.27
pH value 7.89 0.65
p-value N/A N/A
m-value 5.60 mmol/L 0.36
Chloride 10.72 mg/L 1.08

The high degree of automation for water analysis allows an increase in sample throughput, minimizes errors, and guarantees outstanding reproducibility. As the presented system includes sample preparation, the sample only needs to be placed in a beaker onto the rack, and the system runs all analyses (conductivity, pH value determination, alkalinity, and chloride) autonomously. The automatic and accurate addition of the solutions combined with the automated system frees up valuable time of the operator and therefore increases the productivity in the lab.

Author

Metrohm AG

Ionenstrasse
9100 Herisau

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