In the case of very low ionic strength solution such a problem arises. Some specific brand of Metrohm is generally used. I want to know if any other brand will meet the purpose?
I would try the „Ross-Electrode“ (sold by Thermo). This construction used a redox-system as internal and external reference half cells. Thus, avoiding the leakage of silver- or mercury-ions into the sample solution (problematic in biochemistry). Traditional Ag/AgCl or SCE will show a clogging of the diaphragm since complexed silver- and mercury-ions will precipitate as chlorides within the liquid junction due to the dilution with the ultra-pure water. Make sure that the pH-meter has an input impedance of at least 10 to minus 14 amperes.
Thank you Dr. Cammann. I have not tried Ross-Electrode for pH measurement in high purity water. The main criteria of pH measurement in high purity water whose ionic strength is much low is to provide a control minor leaking path of KCl from the pH electrode to the solution. I have got excellent result using a particular brand of Metrohm electode which is designed for that purpose. But the electrode is expensive one and its life period is one year.
Try a combination of a flow-through cell and the electrode you are now employing.
Thank you Dr. Okawa. Will you please elaborate your answer by giving guidelines what type of flow-through cell to be used and how to combine pH electrode to that flow-through cell. If you quote some reference for this I will be very happy.
For example, see this page: http://www.coleparmer.com/Product/pH_electrode_combination_double_junction_sealed_for_flow_through_cell_05662_48/EW-05662-51
You may design and prepare the similar structure for your electrode.
The important point is that the fresh sample water must be flowing continuously. The flow rate is not important.
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