Titrations have the
main advantage that the consumption of the titrant depends
linearly on the concentration of the formed or consumed
acid, leading to more precise results. However, classical
titrations are not suitable for a fast screening of selective
hydrolases for several reasons: (i) the volumes of sample
solutions are very small (less than 500L); (ii) to determine
the kinetic of an enzyme reaction, e.g., to follow a hydrolysis,
the reaction time must be kept constant, which is also not
so easy when classical titrations or even microtitrations
are used; (iii) the dynamic measuring range should
be as wide as possible; in case of classical titrations the
concentration of titrant and sample should be comparable,
which restricts the dynamic range of analysis. From these
considerations follows that non-equilibrium titrations in
a flow-through system and pH detection are an attractive
alternative. FIA titrations have been described first by Ru˚ zˇ icˇka
and Hansen and several methods use spectrophotometric
detection of color indicators resulting in a limited
dynamic measuring range. Here, potentiometric detection
is an interesting alternative because no additional reagents
are necessary. A range of electrodes has been described for
pH determinations in FIA potentiometry