Differential scanning calorimetry drawbacks

The use of a cooling accessory permits XRD patterns to be obtained under subambient conditions. In pharmaceutical systems, the greatest utility of the technique is to monitor the crystallization of solutes in frozen solutions. Conventionally, differential scanning calorimetry has been the most popular technique for the characterization of frozen systems. However, as mentioned earlier, this technique has some drawbacks (i) It does not enable direct identification of crystalline solid phase(s). Moreover, it is difficult to draw any definitive conclusions about the degree of crystallinity, (ii) The interpretation of DSC curves is very difficult if there are overlapping thermal events. Low temperature XRD was found to be an excellent complement to differential thermal analysis in the characterization of water-glycine-sucrose ternary systems. " ... 

In previous chapters, the principles and applications of differential scanning calorimetry (DSC) have been outlined, and it should be clear that the technique is both versatile and extremely sensitive. Using DSC, it is possible to analyze a wide range of systems quickly and cheaply so that thermodynamic parameters may be obtained. These qualities have led to the widespread use of DSC for not only pure research but also for routine thermal analysis. DSC does, however, have some drawbacks. To achieve good thermal contact with a sample, most DSC instruments are equipped with a pair of sample holders into which prepared sample and reference materials are placed. These materials are usually encapsulated in crimped aluminum ampoules, a typical sample mass being 5 to 10 mg. Such a small mass of sample contributes... 

A potential drawback for applications of amorphous ribbons is that, being metastable phases, crystallisation can occur as the working temperature increases, with disastrous effects for the magnetic properties. For these reasons, crystallisation phenomena have been widely studied. The crystallisation temperature, 7, can be readily determined by differential scanning calorimetry (DSC), where it appears as a strong, exothermic... 

A major source of error in determining the degree of crystallinity by differential scanning calorimetry arises from the selection of the baseline under the endothermic peak. The problems associated with this procedure were discussed in reference to heat of fusion measurement in Section IV.D. 1. Differential scanning calorimetry also suffers to some extent from poor sample to sample repeatability, which lowers its precision and accuracy. As with the determination of degrees of crystallinity from density, the presence of fillers invalidates this method. From a theoretical standpoint, the determination of crystallinity from a sample s heat of fusion relies on a simple two-phase model of morphology. These drawbacks and an uncertainty in the heat of fusion of 100% crystalline polyethylene limit the accuracy of this method to approximately 5%. 

---