Thermal analysis Physical-chemical methods

Infrared (IR) spectroscopy is a reliable, fast, and cost-effective analytic technique. It is one of the classic methods to determine the structure of small molecules or fimctional groups. IR is ideally suited for quahtative analysis of polymers and finished products as well as for quantification of components in polymer mixtures. Thermal analysis techniques include physical-chemical methods to study materials and processes under conditions of programmed changes in the surrounding temperature. Thermal volatihzation analysis (TVA) is a technique that analyzes the products formed when, for example, a polymer is heated. It analyzes the polymer itself as well as the volatile compounds released during this heating. In this chapter, we present the application of TVA to biodegradable polymers, especially polylactic acid (PLA), starch, and their mixtures. 

Furthermore, molecular analysis is absolutely necessary for the petroleum industry in order to interpret the chemical processes being used and to evaluate the efficiency of treatments whether they be thermal or catalytic. This chapter will therefore present physical analytical methods used in the molecular characterization of petroleum. 

Differential thermal analysis ("DTA") is a measuring method which makes it possible to study the heat transfer during physical and chemical reactions. This can be done with small samples (usually a few milligrams). This analysis is suited for studying the thermal stability of materials and can in many cases be used to assess the thermal potential of chemical reactions. 

The kinetic and thermodynamic characterisation of chemical reactions is a crucial task in the context of thermal process safety as well as process development and optimisation. As most chemical and physical processes are accompanied by heat effects, calorimetry represents a unique technique to gather information about both aspects, thermodynamics and kinetics. As the heat-flow rate during a chemical reaction is proportional to the rate of conversion, calorimetry represents a differential kinetic analysis technique. The combination of calorimetry with an integral kinetic analysis method, e.g. UV-vis, near infrared, mid infrared or Raman spectroscopy, enables an improved kinetic analysis of chemical reactions. 

Polymorphism is customarily monitored by melting point or infrared spectral analysis. However, other methods, such as X-ray diffraction, thermal analytical, and solid-state Raman spectroscopy, also can be used. It is expected that the sponsor will conduct a diligent search by evaluating the drug substance recrystallized from various solvents with different properties. Either the basis for concluding that only one crystalline form exists, or comparative information regarding the respective solubilities, dissolution rates, and physical/chemical stability of each crystalline form should be provided. 

Thermal analysis is an important technique for determining the physical and chemical properties of polymeric materials. It may be defined as a set of methods used to measure the physical or chemical changes of substances as a function of temperature. Some common thermal analysis techniques are given in Table 4.8.1. 

Thermal analysis methods are defined as those techniques in which a property of the analyte is determined as a function of an externally applied temperature. Regardless of the observable parameter measured, the usual practice requires that the physical property and the sample temperature are recorded continually and automatically and that the sample temperature is altered at a predetermined rate. Thermal reactions can be endothermic (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, chemical degradation, etc.) or exothermic (crystallization, oxidative decomposition, etc.) in nature. Such methodology has found widespread use in the pharmaceutical industry for the characterization of compound purity, polymorphism, solvation, degradation, and excipient compatibility. ... 

Thermal analysis has been and will continue to be widely used for pharmaceutical formulation. due both to its versatility and also the ability to present key information on the physical (and sometimes chemical) structure and behavior. Modem thermal methods tend to be simple to use and. for basic measurements, the amount of training required is often fairly limited. This is clearly an advantage in most respects, although this simplicity of use leads to a danger of underestimating the wealth of information that may be obtained... 

The choice of a HPLC/MS analysis method depends greatly on the characteristics of the sample (i.e. proton affinity, polarity, thermal stability and volatility) as well as the structural information and sensitivity required. The use of various techniques including enzymatic hydrolysis and physical-chemical reactions can assist in achieving the analysis goals for certain compounds. Alternatively, the use of complimentary HPLC/MS techniques such as thermospray and particle beam can be useful for the analysis of a variety of compounds, as demonstrated in this paper. Employing less commonly available instrumentation, such as tandem MS, with thermospray or particle beam can prove valuable in determining structure when other methods are unsuccessful. The further development of existing HPLC/MS techniques and the implantation of new HPLC/MS methods will continue to increase the variety of compound classes that can be routinely monitored with adequate sensitivity and specificity. 

The temperature dependencies of these parameters reveal chemical and physical transformations that occur in the nature of the kerogen materials and the pyrolysis products. Examples of -H NMR thermal scanning of Australian oil shales are presented which illustrate this method of 1h NMR thermal analysis. 

Water molecules are constantly in motion, even in ice. In fact, the translational and rotational mobility of water directly determines its availability. Water mobility can be measured by a number of physical methods, including NMR, dielectric relaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of water molecules in biological systems may play an important role in a biochemical reaction s equilibrium and kinetics, formation and preservation of chemical gradients and osmotic pressure, and macromolecular conformation. In food systems, the mobility of water may influence the engineering processes — such as freezing, drying, and concentrating chemical and microbial activities, and textural attributes (Ruan and Chen, 1998). 

Equipment for thermal analysis is used extensively for the preformulation study. As in the solid-state investigation, interest is focused not only on the chemical change but also on the physical change, which can be illustrated appropriately by thermometric methods. 

With all of the preceding distressing sources of error and limitations, thermal analysis has several incomparable advantages (1). Being a physical method, it may be applied without any knowledge concerning the chemical properties of the main component or the contaminants of the sample. It is sensitive, although not equally sensitive, to all types of contaminants. When the sample may be considered as a binary system, it certainly permits quantitative determination of its content of contaminants. 

Thermal analysis systems A group of analytical methods that evaluate the mineralogy of a sample by measuring the change in some physical or chemical property or reaction product as a function of change in temperature. 

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