Problems with sulfide selective electrode

Xavier P. Cristina dbxcp at fc.udg.es
Mon Jul 28 08:52:03 EST 1997

Hi all

We've been using a Orion selective electrode 94-16 to measure sulfide in 
samples of lake water. The measure ranged from 5 to 50 µM. As read in
the bibliography this method has been used for this purpose by several
scientific groups.Otherwise, in a recent paper we summited in an
international microbiology journal, the referees suggested that our
sulfide results could be overestimated due to sulfur reduction by SAOB
solution.If this was the case our values could be wrong and by no way
corrected, as sulfur was not measured.
We followed the protocols from Orion Intruction Manual, mixing SAOB
solution 1:1 with the sample immediately after taking it. The
potentiometical measures were done during the first 24 hours after
sampling and the samples were kept in the dark. The referees also
pointed out that time of storage of the mixture is basic in this proces
of sulfur reduction. As we haven't got any reference that could explain
this process, we've decided to make you some questions:
Has anybody got any information about this problem? Do you know which is
the critic time of storage before sulfur gets reduced by SAOB? 

Thanks in advance

Xavier P. Cristina
Institute of Aquatic Ecology
Fac. of Sciences. Campus Montilivi
E-17071 Girona. SPAIN
dbxcp at fc.udg.es

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