Titration/Data Analysis; Calculation Of Equilibrium Constants - TA Instruments Nano ITC Series Getting Started Manual

The baseline data, i.e. heat flow in the regions before and after each titrant pulse, shows the power required
to maintain a zero temperature difference between the sample and reference cells.
The baseline in this region is a function of heating by stirring. The baseline is used to calculate the area or
the heat from each pulse in the reaction vessel during the titration or batch reaction. The thermogram
constructed from the integrated peak areas is then used for data analysis.

Titration/Data Analysis

A single titration calorimetric experiment yields heat data as a function of the ratio of the concentrations of
the reactants. Titration data, in the form of heat change versus volume of titrant added, can be examined for
both analytical (thermometric titrimetry) and thermodynamic (titration calorimetry) information.
Other corrections must be made to the heat data to account for heat effects associated with titrant dilution
and any temperature difference between titrant and titrate solutions. These corrections are most easily
accomplished by performing a blank titration experiment and subtracting the blank heat data from the
experimental thermogram.
In the case of quantitative reaction of added titrant, the analysis of the thermogram is quite simple. All
peak areas will be the same (with the possible exception of the last peak) and ΔH calculated from the incre-
mental heat and the number of moles of titrant added per increment. The titrant concentration is calculated
from the total heat divided by the ΔH for the reaction.

Calculation of Equilibrium Constants

The equilibrium constant for a given reaction may be simultaneously determined with the enthalpy change,
if the magnitudes of K and ΔH for the overall reaction taking place in the calorimeter are within certain
limits. The family of curves presented in the figure below shows that increased overall curvature of the
thermogram is generated with decreasing values of the association constant, K .
eq
Figure A below shows the effects of varying magnitudes of the enthalpy change ΔH. Figure B shows the
effects of varying the equilibrium constant K.
B
A
Figure 3 Calculation of equilibrium constants.
Nano ITC Getting Started Guide Page 11