Acquiring Calorimetric Data

Of course, a decisive prerequisite in any meaningful evaluation of calorimetric data is the judicious choice of experimental conditions, the appropriate correction of the data with respect to ubiquitous nonspecific contributions like the heat of dilution or mixing and above all the adequate choice of a model representing the relevant processes in solution. Similar to many other data evaluations where several individual contributions convene to generate a singular output (as e.g. in kinetics) adherence of the experimental data to a certain model does not ultimately prove the model, but surely disproves all non-fitting alternatives. The various options are discussed further below. At this point we shall focus the attention on the production of good quality data that in the end will be all decisive on the success of interpretative attempts. 

Paramount to the experimental setup is the purpose of the calorimetric titration as it dictates the selection of the dimensionless c-value (Eq. (3.7)) [1]. 

In the case depicted in Fig. 3.3. The c-value amounts to 80 and falls well within the range of 5-500 that displays clear sigmoidal curvature and is best suited for the calculation of AH, Kassoc and n in a single experiment. 

In some instances, the precise estimation of the interaction enthalpy AH or the stoichiometry n rather than the affinity constant fCassoc is desired. Then, raising the c-value well over 1000 by an increase of the initial concentration is a beneficial option. The titration curve will then appear as a step (jump) function as in Fig. 3.4 because the titrant added in aliquots from the syringe will be totally converted to the complex in each addition until the reaction partner in the cell is consumed completely. The subsequent injections will only show the spurious heats of dilution and mixing and thus will end in parallel to the molar ratio axis. The jump 

Provided the stoichiometry n is secured by supplementary noncalorrmetric evidence and, furthermore, is unperturbed by high concentrations of the interaction partners, an analysis of the statistical error allows some recommendations to be made for parameter adjustment to optimize the precision [24], Hence, under these prerequisites (which admittedly seldom apply in artificial host-guest systems) the enthalpy AH and association constant Kassoc can be determined to less than 1% relative error in a broad range (10 Kassoc 10 valid for AH, too, when Kassoc 30 just following a simple recipe [23] (i) Use no more than 10 injections of the titrant solution (ii) set the final molar ratio in accord with the empirically determined Eq. (3.8), but not smaller than 1.1 where c is as defined in Eq. (3.7) this requires a crude estimate of the binding constant Kassoc- Table 3.1 lists the digest of 

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An overview of typical calorimetric techniques indicating sensitivities, principal application areas, and the usual data acquired is shown on Table 2.1. A brief summary of advantages and disadvantages of the various tests is also given. The column "principal applications" indicates only the major applications of the respective techniques. In any of the tests listed, it is possible to obtain additional data or to use the test equipment for completely different hazard evaluations once the techniques are fully understood and the tests are run by fully qualified technical personnel. Testing techniques are discussed later in Section 2.3 on Practical Testing. 

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