What is the difference between the symmetric and the asymmetric evaluation principle?
Symmetric curve: The curve has a symmetric profile and the equivalence point is the inflection point of the curve. This curve is evaluated by plotting the first derivative dE/dV versus titrant consumption V. The maximum of the derivative is at the inflection point and indicates the equivalence point. For the automatic evaluation of the symmetric S-curve the titrator provides the appropriate procedure (“STANDARD”). Examples: Acid/base titrations, redox titrations, precipitation titrations Asymmetric curve: This titration curve shows a different profile than the typical symmetric S-curve, and thus a different evaluation procedure is needed. This is based on the Tubbs procedure (see “Fundamentals of titration”, ME-704153). The asymmetry has to be taken into account for curve evaluation. The equivalence point is shifted towards the region with the stronger curvature. The curve is fitted with two circles (better: two hyperbolas). The intersection point of the line connecting the two foci an
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