Heat conduction differential calorimetr

Also DSC instruments of the heat conduction type exist (see, for example, Ross and Goldberg, 1974). If the temperature of the heat sink is increased, heat will flow through the two thermopiles into the two vessels. If heat conductance and heat capacity of the two calorimetric units are the same, we can expect that the differential potential signal from the thermopiles will be zero. However, if the heat capacity differs, for example, between an aqueous solution in the sample vessel and... 

Numerous determinations of differential heats of adsorption have been made, both by direct calorimetric and by indirect thermodynamical evaluations. Generally speaking, these determinations cannot be regarded as highly accurate. For the calorimetric measurement, difflculties are encountered due to the frequently low heat conductivity of the adsorbent at a low pressure, leading to abnormal heat curves as shown frequently in the earlier literature. 

Differential scanning calorimetric runs were conducted on a Du Pont Thermal Analyzer (Model 9900) at an arbitrary heating rate of 10°C/min. Indium standard was used for temperature calibration. 

According to Eq. (16), the difference between the differential heats of solution of two polymorphs is a measure of the heat of transition AH between the two forms. Because enthalpy is a state function (Hess s law), this difference must necessarily be independent of the solvent system used. However, conducting calorimetric measurements of the heats of solution of the polymorphs in more than one solvent provides an empirical verification of the assumptions made. For instance, AH values of two losartan polymorphs were found to be 1.72 kcal/mol in water and 1.76 kcal/mol in dimethylformamide [53]. In a similar study with moricizine hydrochloride polymorphs, AH values of 1.0 kcal/mol and 0.9 kcal/mol were obtained from their dissolution in water and dimethylformamide, respectively [54]. These two systems, which show good agreement, can be contrasted with that of enalapril maleate, where was determined to be 0.51 kcal/mol in methanol and 0.69 kcal/mol in acetone [55]. Disagreements of this order (about 30%) suggest that some process, in addition to dissolution, is taking place in one or both solvents. 

A calorimetric determination of crystallinity can be made by measurement of the heat of fusion using differential scanning calorimetry (DSC). The conversion from heat of fusion to mass crystallinity may be conducted by the total enthalpy method, which is illustrated in Fig. 7.42. It is assumed that only two components exist, and that each of them has a certain... 

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