Gas analysis, evolved

Thermogravimetric analysis (TGA) is a technique that provides quantitative information on the change in mass of a sample as a function of time as it is heated, cooled, or held at constant temperature. TGA alone, however, is not an identification technique for unknown samples. 

The combination of TGA with a mass spectrometer (MS) or a Fourier transform infrared spectrometer (FTIR) allows the nature of the gaseous products formed in the TGA to be investigated online. When several compounds are evolved, the MS or FTIR can track their evolution profiles. Mass spectra and infrared spectra are substance specific. The spectra can be used to characterise the substance or class of substance through spectral interpretation 

TGA-MS High sensitivity coupled with very fast measurement. Extremely small amounts of substances can be detected. Ideal for the online characterisation of all types of volatile compounds. 

TGA-FTIR High chemical specificity and fast measurement. Characterises substances by identifying their functional groups, i.e. the class of substance. Ideal for the online measurement of substances that exhibit medium to strong infrared absorption. 

Evolved gas analysis (EGA) involving coupling of a GC to a MS has been used to identify volatile products formed on heating polystyrene [16-19]. 

Keen and co-workers [20] used EGA to monitor the evolution of additives from rubber and polymers in order to evaluate the effectiveness of encapsulated BHT antioxidant from polyisoprene. The technique involves the coupling of a thermogravimetry mass spectrometry with oxidative DSC. 

In selecting or designing antioxidants for practical situations, problems of loss of antioxidant by both chemical and physical processes may be encountered. 

Chemical loss of antioxidant can occur during processing as the antioxidant behaves in the intended way by stabilising the base polymer. Moreover, if the base polymer is to be crosslinked, the antioxidant may become consumed by interfering with the crosslinking reactions. The net result is that the concentration of antioxidant in the base polymer is reduced, and so the service life of the product is shortened. 

Physical loss of antioxidant can occur during processing of the polymer if the antioxidant is sufficiently volatile at the fabrication temperature. Another effect is that antioxidants may diffuse to the surface, or those which are soluble in molten polymers may become insoluble at service temperatures and may separate out preferentially on the surface. This 

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 

Sample Holder Driving Coil Deflection Sensor 

Evolved gases drawn into Sniffer lube 

Condensation Baffle Profecis balance hang-down wire 

MS has more analytical flexibility than FTIR, but interfacing a thermal analyzer is difficult because of the low operating pressure required for MS. MS instruments typically operate at approximately 10 torr, while thermal analyzers are usually at atmospheric pressure. One approach is to evacuate the thermal analyzer, but the common method 

As indicated in the previous chapter, the TGA technique only informs on the variation of sample mass, but hardly on the mechanisms linked to the decomposition or the reaction. The idea behind the EGA coupling is to analyze the vapours emitted by the sample during the test [39]. Three main gas coupling techniques are used for such an investigation as described in Table 2.6  

Mass and MS spectrum TGA-MS In TGA-MS, the TG is connected online with a mass spectroscopy detector to determine the nature and amount of volatile product emitted by the sample during a thermogravimetric experiment 

Condensation baffle protects balance and hang-down wire 

EGA is used for materials characterization, polymer analysis, characterization of oil shale, oxidation and reduction studies, evaluation of catalysts, and many other applications. 

In the environment, persistent organic pollutants such as polyaromatic hydrocarbons have been shown by TGA-GC-MS to exhibit a six- to tenfold increased partitioning to the water phase in an octanol-water solution in the presence of Xi02 nanoparticles, suggesting that the 

The mass spectrum of evolved gases (up to MWs of 1024 Da) can be obtained to provide identification of the structure with no condensation during transfer between the thermal analyzer and the mass spectrometer. (Courtesy of Setaram Instmmentation, SA, Caluire, France, www. setaram.com.) (b) A different commercial thermogravimetry (TG)-GC-MS system, showing the Netzsch TG 209 on the right, connected to a GC-MS via an external transfer line. (Courtesy of NETZSCH Instruments, Inc., Burlington, MA, www.netzsch-thermal-analysis.com.) 

As discussed earlier, instrumentation is useful in studies of thermal and chemical stability of polymers, including the following (see Table 9.2) TGA, DTA, DSC, TVA, and EGA (including TGA-GC, TGA-FT-IR spectroscopy, TGA-GC-MS). 

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Evolutionary technology Evolved gas analysis Ewens-Bassett numbers... 

Measurements of product gas evolution, mass loss or evolved gas analysis may all be used to study the kinetics of a solid—solid interaction provided that there is strict adherence to the condition that gas evolution occurs concurrently with the solid state process. Clearly this approach is only applicable if there is direct experimental support for a single step process. For example, carbon dioxide release is identified [410] as being... 

Thermal-programmed solid insertion probe mass spectrometry (TP-SIP-MS) has been proposed [247,248], in which the solid insertion probe consisting of a water-cooled microfumace enters the mass spectrometer via an airlock. The sample is contained in a small Pyrex tube (i.d. 1 mm, length 20 mm). The TIC trace gives a characteristic evolved gas profile for each compound in a mixture of materials, and the mass spectra associated with each TIC peak give a positive identification of that component as it is vaporised. TP-SIP-MS is appropriate for analysis of small solid particles which are volatile, or produce volatile decomposition products. The technique is a form of evolved gas analysis. 

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. 

A thorough study of the mechanism of degradation of several fire retardant melamine salts is carried out using thermogravimetry, evolved gas analysis and spectroscopic characterisation of the products of degradation. 

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,... 

This is the primary degradation process accompanying processing of the polymer. The early stage of the dehydrochlorination process is uncomplicated by interfering processes. The only product observed by evolved gas analysis is hydrogen chloride (scheme 1). The sample... 

Air Adsorb to qnartz filter Evolved Gas Analysis 10-g NR Daisey and Gnndel 1991... 

Daisey J, Gundel L. 1991. Tracing the sources of indoor aerosols using evolved gas-analysis. Aerosol Science and Technology 14(l) 25-32. 

Evolved gas analysis QEGA). Temperature programmed (5°C/min) mass spectrometrlc (MS) techniques were used to analyze the volatile products formed during sample heating. 

Physical State Evolved Gas Analysis Mass spectrometer Gas chromatography IR transmission Film sensors External sample analysis... 

Evolved gas analysis Nature and composition of gas liberated during thermal analysis. Gas analyzer... 

The main benefits of the mass chromatographic system can be summarized as follows. (1) Precise quantitative analysis can be performed without individual peak calibration. (2) Molecular weights are readily determined for compounds that can be gas chromatographed. (3) Peak identification is usually possible by the combined use of molecular weight and retention data (when such data are available). (4) The unique trap design and dual aspects of the instrument are ideally suited for evolved gas analysis from thermal analyzers, catalyst studies, etc. These benefits will be discussed throughout the paper with emphasis oriented to the polymer field. 

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. 

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