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How to differentiate borohydride and boric acid if both of them are present together?

I have a problem now with analysis of boric acid in waste water. But an amount of borohydride is present there. I want to know whether we have a method to differentiate these two species of boron?

Thank you very much for your help.

Richard Wu
San Diego State University - San Diego, California, USA
2006

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2006

Richard,

I know there is a procedure where mannitol binds with the boric acid and then the solution is titrated with base. But I'm not sure whether borohydride would be considered an interferent.

Another option is to measure borate ion with ion chromatography.

Terry Tomt
- Auburn, Washington

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2006

Borohydride ion is only stable in water which is extremely alkaline. I mean at the 50 - 100 g/l sodium hydroxide level.

You could acidify an aliquot of the sample and volumetrically measure the evolved hydrogen gas. The borohydride concentration can be calculated from this. Then, run total boron on your sample, and subtract the B that is present as borohydride to get your borate result.

Dave Wichern
Consultant - The Bronx, New York