DTA thermogram

Construction of a Phase Diagram ly Use of Several DTA Thermograms (DTA Runs 1 through 7)... 

Still einother use to which DTA has been employed is the characterization of amorphous materials. The following shows a typical DTA thermogram obtained when a powdered sample of glass is run as shown in the following diagram ... 

Differential thermal analysis proved to be a powerful tool in the study of compound polymorphism, and in the characterization of solvate species of drug compounds. In addition, it can be used to deduce the ability of polymorphs to thermally interconvert, thus establishing the system to be monotropic or enantiotropic in nature. For instance, form I of chloroquine diphosphate melts at 216°C, while form II melts at 196°C [18]. The DTA thermogram of form I consists of a simple endotherm, while the thermogram of form II is complicated (see Fig. 4). The first endotherm at 196°C is associated with the melting of form II, but this is immediately followed by an exotherm corresponding to the crystallization of form I. This species is then observed to melt at 216°C, establishing it as the thermodynamically more stable form at the elevated temperature. 

Fig. 4 DTA thermogram of chloroquine diphosphate, form II, illustrating the melting endotherm of form II (196°C), recrystallization to form I, and final melting endotherm attributable to the converted form I (216°C). (Data adapted from Ref. 18.)...

A DTA thermogram of dobutamine hydrochloride, at a heating rate of 5°C per min. in a nitrogen atmosphere of 40 cc per min., shows (figure 1) an endotherm at 196°C which appears to indicate a melt. 

Wendlandt has provided an extensive compilation of conditions and requirements that influence the shape of DTA thermograms [18]. These can be divided into instrumental factors (furnace atmosphere, furnace geometry, sample holder material and geometry, thermocouple details,... 

Fig. 4.5. DTA thermograms sulfathiazole, Form-I (lower trace) and Form-II (upper trace). Adapted from Ref. [24].

Quantitative analysis of the DTA thermograms was used to calculate the enthalpy of fusion for each form, with this information then being used to identify the order of relative stability. Some of these species were found to undergo phase conversions during the heating process, but others were noted to be completely stable with respect to all temperatures up to the melting point. 

Figure 3. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) thermograms of benzoic acid.

The technique of differential scanning calorimetry (DSC) is very similar to DTA. The peaks in a DTA thermogram represent a difference in temperature between the sample and reference, whereas the peaks in a DSC thermogram represent the amount of electrical energy supplied to the system to keep the sample and reference at the same temperature. 

The DTA thermograms indicate for each type a shifting downwards of the exotherm at the 1.0 x 10SK level. The IR spectra for the various Pb azides reveal that a form of Pb carbonate is evident at the higher exposure. This is probably the reason for the lower values in the vacuum stability test listed is Table 11. Another interesting feature was the formation of ammonium nitrate on top of each Pb azide and thallous azide irradiation capsule (as shown in Fig 16) subjected to over 109R... 

It has been reported that pyrolysis gas chromatographic techniques could be used to differentiate between block and random copolymers (18). However, it was not possible to distinguish between the block copolymers and mixtures of polystyrene and the alternating copolymers of styrene and maleic anhydride by the PGC technique used in this investigation. However, differences were noted in the DTA thermograms of the alternating copolymer, the block copolymer, and the mixture of polystyrene and the alternating copolymer. 

Differential thermal analysis (DTA) thermograms of ( )-etodolac sodium salt exhibited endothermic transitions around 80,120, and 297°C and an exothermic transition around 83°C [12]. The exothermic phase change was observed after exposure of the sample to moisture, indicating conversion of the amorphous form of ( )-etodolac sodium salt to a crystalline phase. In contrast, the thermogram of (+)-etodolac sodium salt, after exposure to moisture, showed endotherms at 60, 80, 120, and 297°C, indicating that the salt contained methanol, acetonitrile, and water. There was no sign of degradation product formation. 

Figure 2. DTA thermograms of Neoprene W-g-PTHFs. Scan rate = 20°C/min. The numbers on the curves indicate the percent PTHF in the polymer.

Figure 6.1, a DTA thermogram of pure (99.9%) HMX, is a good example. The pronounced endotherm (dip) is due to a change in crystal form (a phase transformation) at the temperature shown ( 200 C). Soon after that, decomposition becomes quite evident, and at around 250 C the sharp break in the curve... 

The simplest and most straightforward application of thermal analysis is concerned with studies of the relative stability of polymorphic forms. For example, DTA thermograms enabled the deduction that one commercially available form of chloroquine diphosphate was phase pure, while another consisted of a mixture of two polymorphs. DTA analysis was used to demonstrate that in spite of the fact that different crystal habits of sulfamethazine could be obtained, these in fact consisted of the same anhydrous poly-morph.f In a study aimed at profiling the dissolution behavior of the three polymorphs and five solvates of spironlactone, DTA analysis was used in conjunction with powder X-ray diffraction to establish the character of the various materials. ... 

Polymers underwent thermal decycllzatlon at 420 to 485°C regardless of blsmalelmlde structure and DTA thermograms of polylmldes prepared photochemlcally closely resembled those... 

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