Titration curves, process design

In [LJ-control maps the substitution of one ligand by another one results in a change of the range of existence of the manifold intermediates. This change can be expressed by the ligand-property imluced shift of the titration curves identified by the relative position of their inflection points Lq s on the log (lL o/[Ni)Q) scale. These characteristic shifts provide information on the thermodynamic selectivity governed by the association processes only. This type of analysis is designated by . 

The first step in designing a pH s stefn is to generate a titration curve at the process temperature with enough data points to cover the range of operation and show the curvature within the control band (absolute magftitude of the difference beitveeit the maximum and minimum allowable pH). 

Automatic titrators that are electronically equipped to compute the first and second derivative of pH with respect to time, and hence reagent flow, can automatically locate the equivalence point. The first derivative, which is the slope of the titration curve, reaches a maximum at the equivalence points. The second derivative changes sign at the equivalence points. A plot of first derivative helps in the control system design because it is indicative of the pH process sensitivity. Figure 3-2a shows a plot of the first derivatives for the weak acid and weak base titration curv e in Figure 3-le. For more information on automatic titrators, consult Reference 3.3. 

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