The permanganate index is used to evaluate the quality of different types of water, e.g. drinking water, mineral water, spring water, and table water. It is determined in accordance with DIN EN ISO 8467 (DIN 38409-5).
For titrimetric determination, the water sample is heated with a KMnO4 solution of known concentration and sulfuric acid in a boiling water bath for 10 minutes. In the process, some of the permanganate oxidizes the oxidizable constituents in the water. The exact consumption of permanganate is determined by adding an excess of sodium oxalate solution and then titrating the excess oxalate with permanganate solution.
The determination of the permanganate index is a standard application performed in almost all water laboratories but it is not without snags. In particular, keeping the quality of sample preparation consistent – including the time-critical heating of samples – is a challenge, especially if it is done manually under the pressure of a high sample throughput.
The method developed by Metrohm solves this problem efficiently and reliably. The key lies in a heatable, external cell, with which the heating of the samples is handled automatically. Users just have to place the samples on the rack of the sample processor and start the system. The transfer of the sample to the external titration cell and all the other sample preparation steps as well as the titration itself, are performed automatically ensuring highest reproducibility and consistent quality.