Differential scanning calorimetry baseline

Figure 17.1 Thermal unfolding of bamase measured by calorimetry and spectroscopy. The heat capacity of bamase (trace A) was measured using differential scanning calorimetry with a baseline (trace B) of buffer versus buffer Tm is 310.9 0.01 K, A D-N(cai) = 98.4 0.2kcal/mol, and A//D N(vh) = 98.1 0.3 kcal/mol. The ellipticity at 230 nm in the circular dichroism (trace C) under identical conditions fits Tm = 310.5 0.1 K, and A//D N(vh) = 93 3 kcal/mol (equation 17.5).

The purchased hydrides were all subjected to characterization in their as-received state, using both differential scanning calorimetry (DSC) and thermovolumetric analysis (TVA). The baseline data from the two methods of characterization, shown in... 

Differential scanning calorimetry was used to measure both the extent of cure as well as the progress of enthalpy recovery in the neat epoxy resin. A Perkin Elmer DSC-2 differential scanning calorimeter equipped with a scannlng-auto-zero unit for baseline optimization was utilized to measure the heat capacity of the... 

Because of the usual experimental ranges of crystallinity, the appearance of the baselines in the study of semicrystalline polymers is not very frequent [36, 37]. Therefore, the crystalline volume fraction should be obtained by other alternative techniques such as, for example, differential scanning calorimetry. In this way, if the crystallinity in volume is known, it is possible to obtain the lost baseline [37, 38]. However, if the crystallinity is either low or high, it is possible to directly obtain the baseline for which it is foreseen that the morphology is solved [36]. For example, Vonk and Pijpers and Vonk and Koga worked at high crystallinities and they observed the aforementioned baselines [39]. 

The second representation of the transition temperature, Tb, utilizes the onset of the transition as estimated from the differential scanning calorimetry (DSC) curve in Figure 5.1C, as estimated by the intersection of the initial baseline and the initial rise of the curve. 

In this paper, a thermodynamic phase transition is studied using Differential Scanning Calorimetry (DSC). This phase transition, which will be described according to the current thermodynamic theories as a first order or a second order one, is recorded on the DSC trace as an anomalous change in the differential power ZP, different from the normal IP variation only due to the heat capacity of the material. This variation, sharp or smooth, will be called the "transition peak". We define the height h of the peak as the distance between the heat capacity trace, or baseline, and the maximum during the course of the phase transition. In the case of a pure second order phase transition, this height is the diffe-... 

The most extensively used methods for monitoring these heat induced changes in fibers are differential thermal analysis (DTA) and differential scanning calorimetry (DSC). In DTA, both sample and inert reference are heated at the same rate by the same heat source. When a thermally induced transition occurs in the sample, a temperature difference between the sample and reference results can be recognized. A plot of the difference in temperature between the two against increasing applied temperature exhibits deviations from the initial baseline, depending on... 

The most detailed thermodynamic analysis of protein structure stability is based on differential scanning calorimetry (DSC). In a DSC experiment, the heat capacity Cp of a sample is monitored while heating (or cooling) the sample. Figure 13.13 shows a typical DSC thermogram for heat-induced denaturation of a protein in solution. The thermodynamic observables are the temperature of denaturation (the temperature at half-peak area), the enthalpy change An, d (T involved in the denaturation process (the area under the peak), and the change in the heat capacity A,, dC of the solution (the shift of the baseline). 

First, we need to mention that the word baseline in differential scanning calorimetry has three basic meanings (1) the instrumental baseline, which is the DSC curve recorded with two empty pans (2) the extrapolated part of the DSC curve during a transition over which the peak should be integrated and (3) the pre- and postmelting baselines (see Section 2.7). 

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%. 

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