I based this on my 2 minute crash course in Karl Fischer reactions - :). Your translation looks fine to me too.
http://en.wikipedia.org/wiki/Karl_Fischer_titration

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Note added at 15 mins (2008-10-11 17:51:20 GMT)
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or "... in the solvent", the meaning is the same in the end.

Creo que "dar un efecto nulo a.." es una manera rebuscada de decir "anular [i.e. reducir lo máximo posible] el contenido de agua"



In carrying out this method, a solvent is generally initially taken and, in order to remove the water content, is titrated to the end point with Karl-Fischer solution. A
specific amount of the sample to be examined is then dissolved in the
solvent and titrated with the Karl-Fischer solution until the end point is
reached. The water content is then calculated from the amount of the
sample, the consumption of Karl-Fischer solution and the factor of the
solution.(...)
The solvents are employed either on their
own or as mixtures, in order to improve the solution properties for
certain groups of substances or to suppress interfering side reactions.
http://www.patentstorm.us/patents/4874709/description.html



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Note added at 34 mins (2008-10-11 18:10:32 GMT)
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suppress


the water content of/in the solvent

--- on the coulometric reading?