A PROCEDURE FOR THE ROUTINE DETERMINATION OF FLUORINE IN POTABLE WATERS CONTAINING IRON, MANGANESE, ALUMINUM, AND CHLORINE

¹ Department of Chemistry, Indiana University, Bloomington, Ind.

The Sanchis-Scott method for the determination of micro amounts of fluoride in potable waters has been modified to permit accurate analysis for fluoride in the presence of iron, manganese, aluminum, and chlorine, which substances interfere in the unmodified Sanchis-Scott method. Chloride, sulfate, alkalinity (expressed as carbonate), and phosphate are tolerated to the same limiting concentrations for noninterference as in the original Sanchis-Scott method.

The modification involves a preliminary treatment of the water sample being analyzed for fluoride by the conventional Sanchis-Scott method with thioglycolic acid. Ferric iron, manganic manganese, and elementary chlorine are reduced to ferrous iron, manganous manganese, and chloride ion, respectively. In the reduced condition, these elements do not interfere with the accurate determination of the fluoride ion by the conventional method.

The fact that the interference of aluminum in the Sanchis-Scott method of fluoride analysis decreases with decreasing concentration of the aluminum ion makes it possible to determine the fluoride accurately by the proper dilution of the sample taken for analysis.