Evolved gas analysis EGA

Schole and co-workers [22] reported on polymer characterisation using an oxidative degradation method. In this method, the oxidation products of the polymers are produced in a short pre-column maintained at 100-600 °C just ahead of the separation column in a gas chromatograph. The oxidation products are swept on to the separation column and detected in the normal manner. 

As pointed out above, accumulatory pressure and weight loss measurements usually refer to the total reaction. When there are several volatile products, it is necessary to identify all components and investigate progressive changes in gas composition. Quantitative determinations of the amounts of each product (EGA) should, ideally, be combined with measurements of the total extent of reaction, although Gam [143] has recommended caution in the interpretation of results from simultaneous measurements. 

The ICTAC definition of EGA a technique in which the nature and/or amount of a volatile products released by a substance are measured as a function of temperature as the substance is subjected to a controlled temperature programme is unsatisfactory in describing the current practice of EGA as a TA technique. In many ways it is too broad, since it includes other techniques such as pyrolysis-GC, and in other ways too narrow, as it would exclude studying the changing nature of the gas stream as it is passed over the sample, as in catalytic studies. The definition does not require an evolved gas analyser to be coupled to another technique, but in practice this is nearly always the case. This section will deal with EGA as it is usually carried out, which is simultaneously, combined with another technique. The commonest combinations are those with TG and TG-DTA/DSC, where EGA assists in interpreting the chemistry of the events leading to weight losses. 

There have been few reviews of the topic as a whole and only one book dedicated to it. The technique is, however, widely used, though the subject matter is dispersed through the literature, and not readily found. There seems to be a problem in correct choice of keywords the official Chemical Abstracts term, thermal analysis - evolved gas , is rarely used, and searches using this are disappointing. 

There has been a multitude of approaches to EGA, ranging from simple methods for answering a particular need to sophisticated research tools. Nearly all TA instruments use a flowing purge gas, which contains the chemical information that is sought. At the simplest level, holding a piece of wet litmus paper, or other indicator in the effluent stream from the instrument, may answer the question at hand. Beyond this, almost every type of gas detector/analyser has been linked to every type of TA equipment, and most manufacturers offer one or more methods for EGA, usually in combination with TG or TG-DTA/DSC. The approach taken in any instance depends on the information required, and there is no truly universal solution. 

Gas chromatography (GC) has been used, when the main advantage is its ability to separate mixtures. Conclusive identification of the components would be possible if a mass spectrometer (MS) was connected to the GC detector. GC is necessarily a batch technique a portion of the gas 

Both FTIR and MS require a powerful data system which, in addition to controlling the equipment, and displaying data, may also have libraries of standard spectra to assist identification. A complete integration of the TA and EGA software is unfortunately rarely achieved. The literature up to 1997 on the techniques and applications of TG-IR has been summarised by Materazzi and excellent reviews of the use of MS for EGA are available. °  

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Although the majority of studies focus on the solid state, many applications focus more or additionally on the volatile products arising from polymer degradation. Evolved gas analysis (EGA) from thermal analysers and pyrolysers by spectroscopic and coupled chromatography-spectroscopy techniques can be particularly important from a safety and hazard viewpoint, since data from such measurements can be used to predict toxic or polluting gases from fires, incinerators, etc. 

The ability of the new precursors to decompose thermally to yield singlephase CIS was investigated by powder XRD analysis and EDS on the nonvolatile solids from the TGA experiments of selected compounds. Furthermore, using TGA-evolved gas analysis (EGA), the volatile components from the degradation of the SSPs could be analyzed via real-time fourier transform infrared (FTIR) and mass spectrometry (MS), thus providing information for the decomposition mechanism.3 The real-time FTIR spectrum for 7 and 8 shows absorptions at approximately 3000,1460,1390,1300, and 1250 cm-1 (see Fig. 6.7). 

Evolved gas analysis (EGA) is based on the study of gases or volatile breakdown products emitted by a sample on heating. The identity and properties of the volatile materials emitted serve as a basis for the analysis of the sample. One particular technique of EGA which has attracted sub-... 

Evolved gas analysis (ega), 14 234 Ewens-Bassett numbers, 17 391, 392 Examiners citations, 18 237, 238 Exanta, 4 100t, 102 Excess properties, ideal mixture and,... 

Photoelectron spectroscopy (ESCA) and thermal evolved gas analysis (EGA) have been applied to characterize sulfur- and nitrogen-containing species in atmospheric particulate matter. Particulate amines and amides previously identified only by ESCA have been detected by EGA, a bulk method, for the first time. EGA and ESCA results suggest the existence of a sulfate similar to ammonium sulfate but with some of the ammonium ions replaced by a charged organic nitrogen complex. 

TABLE 18.3. Select NOM Characterization Studies by Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Differential Thermal Analysis (DTA), and Evolved Gas Analysis (EGA)... 

It should be noted in conclusion that a thermoanalytical screening of 35 tetrazoles based on the data of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and evolved gas analysis (EGA) has been performed <1999MI168> (cf. Section 6.07.5.2.1). 

Pyrolysis results are very important for coal characterization, as all conversion processes of coal such as combustion, liquefaction, and gasification start with a pyrolytic step. For this reason, pyrolysis was frequently used for the analysis of coals [17,18). Pyrolysis data were correlated with coal composition, coal characterization and ranking [18a], prediction of coal reactivity as well as of other properties related to coal utilization. Techniques such as Py-MS, Py-GC/MS with different ionization modes, Py-FTIR, or evolved gas analysis (EGA) [19] were described for coal analysis. Programmed temperature pyrolysis is another technique that has been proposed [17] for a complete evaluation of the two types of molecules present in coal. 

Evolved gas analysis (EGA) can provide information on the rates of formation of individual gaseous products. 

Emanation thermal analysis (ETA) involves the measurement of the release of inert (usually radioactive) gas from a solid sample, as a function of temperature. The rate of such gas release is essentially an indication of the changes taking place in the sample, and a comparison of ETA data with those of other thermal analysis techniques, particularly TGA and evolved gas analysis (EGA), provides information on the microstructure of the sample material. However, most of the solid samples studied by ETA are spiked ... 

The interpretation of TG observations frequently requires support from complementary measurements. Important methods to confirm the identities of rate processes investigated by TG often usefully include enthalpy measurements (DSC and DTA), evolved gas analysis (EGA), structure determinations (x-ray diffraction), microscopy (textural changes of solids), etc. In particular, within the pharmaceutical arena, there is often a tendency to assume that mass losses are exclusively due to water it is recommended that such an assumption should be made with care. 

The application of thermogravimetry to a particular problem is possible if a mass-change is observed on the application of heat. If no mass-change is observed, then other thermal techniques such as DTA, DSC, TMA, and so on, may have to be employed. If the mass-change is very small (< 1%), then perhaps other techniques such as evolved-gas analysis (EGA) may be more useful. Mass-changes (generally mass-losses) which can be detected by TG techniques are summarized in Figure 4.1. 

Evolved Gas Analysis (EGA). A technique of determining the nature and amount of volatile product or products formed during thermal analysis. 

Recently, McAdie (6) published the recommendations of ICTA concerning evolved gas detection (EGD) or evolved gas analysis (EGA) curves. These recommendations are as follows ... 

The physical property measured and the corresponding thermal analysis technique are tabulated in Table 1.1 (3) and further elaborated on in Chapter 13. Notice that under the physical property of mass, thermogravimetry (TG), evolved gas detection (EGD), evolved gas analysis (EGA), emanation thermal analysis (ETA), thermoparticulate analysis, and others are included. Similar considerations can be included in the physical proparties of optical characteristics, electrical characteristics, magnetic characteristics, and so on. The definitions of each individual technique are given in the chapter in which they are discussed. A select number of the thermal analysis techniques are summarized in Table 1.2. Each technique is tabulated in terms of the parameter measured, a typical recorded data curve, the instrumentation needed, and the chapter in which it is described. 

TGA experiments on polymeric systems often show complex TGA mass/temperature curves in which multiple decomposition products correspond with the weight change observed (see, for example, Figure 2.10). TGA has thus proven to be an excellent quantitative technique but less suitable for specification. This drawback can be eliminated if the components which are causing the mass losses detected, are also analysed simultaneously, the so-called evolved gas analysis (EGA). Several TGA-EGA systems are described in literature, analysing the evolved gases with different techniques i.e. thermal conductivity, cold-trapping followed by GC, mass spectrometry (MS) and infrared (FTIR). MS and FTIR have proven to be the most powerful techniques [3, 10]. 

The evolution of gas from a thermal analyzer such as a TGA, DTA, or DSC may be determined using evolved gas detection (EGD) or, if qualitative or quantitative analysis of the gas is required, evolved gas analysis (EGA). These techniques are essentially a combination of thermal analysis and MS, tandem mass spectrometry (MS-MS), GC-MS or other... 

Gas flow Evolved Gas Analysis EGA The nature and/or amount of gas / vapour is determined. 

Every two years, a fundamental review on thermal analysis is published in Analytical Chemistry, in which the development of new methods and the main applications to calibration, thermodynamics, kinetics, polymers, inorganics, pharmaceutical, biological, foods, etc. are reported [1-3]. Several articles regarding coordination compounds are cited and critically described. An update of the applications of evolved gas analysis (EGA), coupled to the thermoanalytical instruments, is also published every four years, and many studies on coordination compounds are cited [4-7]. 

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