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SOP to determine Fluoride levels in brackish water

I am currently a college student in an environmental chemistry course. I am testing the levels of inorganic contaminants in an estuary environment that is undergoing construction. I am looking for a SOP as to how to determine the levels of Fluoride in these water samples.

Jessica Landkrohn
- Jacksonville, Florida, USA
2005

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2005

If you have access to a fluoride ion selective electrode, these samples can probably be run directly. It will be necessary to make up fluoride standards in an artificial sea water matrix. Also, realize that there is about 1.5 ppm naturally occurring fluoride in ocean water.

If you do not have access to the probe, then there are various colorimetric methods. All of these will require the samples to be distilled, with the addition of silver sulphate to keep the chloride from distilling over. The distillation involves mixing the sample with sulfuric acid, bringing the mixture to a boil, then collecting the distillate until the mixture comes to a temperature of 180 C. These distillations are time consuming and a little dangerous.

Details of both methods, and the distillation procedure, can be found in "Standard Methods for the Examination of Water and wastewater". This should be in your college library.

Good luck.

Dave Wichern
Consultant - The Bronx, New York