Polarography applied to nitrate determination in sanitary water analysis

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Virginia Polytechnic Institute


The purpose of the investigation was to determine the interfering effect on the polarographic method of nitrate analysis of certain chemicals commonly employed in the water purification process. Chemicals tested consisted of coagulants, a disinfectant, and an algaecide. A. “synthetic” water of known chemical consistency was used for diluting purposes.

The investigation consisted of two phases; (1) establishing a standard curve with 95 per cent confidence limits of nitrate concentration versus current reading, and ( 2) determining the amount of nitrate recovery in samples containing known nitrate concentrations and certain chemical additives. A further investigation was made of the effect of chemicals revealing a pronounced interference during the initial test.

The results obtained indicated that ferric chloride, ferric sulfate, chlorine, and copper sulfate did not interfere with the nitrate analysis. Alum and ferrous sulfate caused a significant interference. The loss in nitrate recovery due to the presence of alum in solution was found to be directly proportional to the alum concentration. Nitrate recovery was reduced from 0 to 10% by alum dosages of 0 to 10 gpg respectively. Although ferrous sulfate caused considerable reduction in nitrate recovery, this is readily explained since ferrous sulfate may be used for the destruction of nitrate in polarographic procedure.

When a number of samples were analyzed, the average time required was about 20 minutes per sample. Thus, the time required to perform a nitrate analysis by the polarographic method compares favorably with other methods of analysis.