TG-MS Coupling

During a long period, the main difficulty in the TG-MS coupling has been to define the right interface that will solve the following technical coupling problem  

To solve these different technical requirements, two different interfaces are today available, according to the mass analysis to be performed  

The transfer line is made of a very thin silica capillary contained in a heated jacket to prevent the condensation, especially at the outlet of the furnace (Fig. 2.38). A fraction of the gas emitted by the sample is picked as closed as possible from the 

TGA crucible to avoid gas dilution. The gas is then transferred through the capillary towards the MS detector within 100 ms. 

The MS detector will provide a spectrum for each injection. According to the sample under study in the TGA, two situations can occur  

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Courtault [137] has critically considered calibration of TG, MS and the TG-MS coupling. The TG (-MS) apparatus is often calibrated with calcium oxalate monohydrate. Bart and co-workers [25] have discussed critically the calibration and interlaboratory reproducibility of TG-MS. 

Courtault [137] has described quantitative aspects of TG-MS coupling, which is still a difficult technique. Dyszel [153] has determined the styrene content in styrene-butadiene... 

Thermogravimetry can be coupled with DSC. Most companies offer the TG-IR or the TG-MS coupling.f Synergic chemical analysis by coupling TG-FT-IR, TG-MS or TG-GC-MS has been recently discussed. Fig. 5 demonstrates the ability of TG-MS for the study of dehydration and decomposition of calcium oxalate dihydrate. The steps correspond to the dehydration into anhydrous calcium oxalate, followed by the transformation into calcium carbonate then by the formation of cacium oxide. ° The sample... 

Bart et al. [311] have reviewed the essential design criteria for TG-MS allowing routine application for polymers. As to hardware, in TG-MS couplings both vacuum and gas atmosphere mass flow... 

Major drawbacks of TG-MS are cost and method standardisation. Although one cannot properly speak of a standardised TG-MS coupling technique this does not necessary constitute a problem. As in case of PyMS there are good reasons to expect that a variety of TG-MS couplings have a future. 

TG-MS couplings are increasingly used by the rubber industry, especially since aromatic plasticisers are toxicologically suspect. Kaisersberger et al. [411] have reported detection of nitrosamine... 

As in the TG-MS coupling, the time of transfer is very short. Caution has to be taken to avoid any condensation in the transfer line. 

The same investigation of calcium oxalate, described previously with the TG-MS coupling, is used to see the difference between the two coupling techniques (Fig. 2.41). 

As seen before with the TG-MS coupling, a fraction of CO2 is detected during the second loss, and a fraction of CO during the third mass loss, indicating the presence of some trace of air in the furnace during the experiment. 

Applications In most polymer/additive analysis applications, a QMS is applied in view of its ease of use, relatively low cost, and coupling with chromatography (Section 7.3). The ability of QMS to cope with large solvent volumes flowing into the ionisation source for extended periods of time and ease of interfacing - both to computers and chromatographs - makes it the choice for multi-user systems, and has facilitated hyphenation with GC, LC and TG. Consequently, QMS are a mainstay of GC-MS, LC-MS and TG-MS. 

This chapter summarizes results obtained during the past 5 years, on the design, preparation and study of titanium and vanadium compounds as candidate precursors to TiC, TiN, VC, and VN. The study of the precursor molecules was conducted through several steps. After their synthesis, thermoanalytical studies (TG-DTA), coupled to simultaneous mass spectroscopic (MS) analysis of the decomposition gases, were carried out to determine their suitability as precursors. CVD experiments were then conducted and were followed by characterization of the deposits by scanning electron microscopy (SEM) energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron microprobe analysis with wavelength dispersion spectroscopy (EPMA-WDS). 

Materazzi, S. (1998). Mass spectrometry coupled to thermogravimetry (TG-MS) for evolved gas characterization A review. App/. Spectrosc. Revs., 33,189-218. [251] Mathieu, J. P. (1973). Vibration spectra and polymorphism of chiral compounds. / Raman Spectrosc., 1,47-51. [224]... 

The TG-MS assembly consisted of a double-focusing DuPont 21-491 Mass spectrometer coupled through a single-stage glass jet separator to a DuPont 951 Thermal Gravimetric Analyzer which was attached to a DuPont 990 Thermal Analyzer Console. 

Zitomer (67) was the first to describe the coupling of a thermobalance to a time-of-flight mass spectrometer and a magnetic sector mass spectrometer. This technique eliminated the practice of collecting or trapping fractions for subsequent analysis and also permitted careful control of the furnace atmosphere. One of the important features of the TG-MS system is its relatively short dead time, that is, the time between product evolution and introduction into the mass spectrometer ion source. Under proper flow conditions, this time is of the order of seconds. There is also less probability of the formation of secondary reaction that can lead to products other than those initially evolved. 

Figure 8.16. TG-MS with a chemical ionization source as described by Bamngarmer and Nachbaur (74). 1, thermobalance 2. furnace 3,3-way valve 4. reaction gas cylinder 5. rotary-pumps 6, coupling line 7. quadrupole mass spectrometer 8. Cl-ion source 9. metering valve 10, ionization gauge 11, analyzer diffusion pump 12. Cl diffusion pump.

Chiu and Beattie (147-149) have described the coupling of a thermo-balance to a mass spectrometer so that simultaneous TG-MS data can be obtained. They used different techniques to sample the evolved gaseous decomposition products ranging from differential trapping 1147), total condensation of the pyrolyzate (149), to continuous sampling or monitoring of the evolved products (148), mainly from heated polymeric samples. 

Other techniques may be coupled with thermogravimetry to provide very useful data and to confirm supposihons. One such instrument combines DSC and TG (simultaneous DSC/TG) and may facilitate the elucidahon of unexpected events obtained from a DSC investigation alone. Other examples of valuable coupling of instmments include TG-FT-IR, TG-Raman, and TG-MS, where the gases that may be produced during a TG inveshgahon are analysed by an FT-IR, Raman, or mass spectrometer, respectively, that have been linked in sequence to the TG instmment [72]. 

From on-line coupled TG-MS and TG-FTIR measurements, in combination with quantitative chemical analysis, the chemical formula for an unknown bismuA oxalate compound was deduced to be Bi(NH4)(C204)2 3.71(6)H20 by Vanhoyland et al. [78], Solution of the crystallographic structure on the basis of X-ray powder data proved this formula to be correct. Bi is 8-fold coordinated by oxygen from the oxalate anions. Because these BiOg polyhedra do not share any edges or vertexes, an open framework is formed with water and ammoniiun molecules between. As a result, water can easily be removed, which is clearly indicated by the rapid initial mass loss in the TG cxu e. 

Lu et al. [94] applied TG-DSC-MS coupled techniques to make a simultaneous characterizing study of the metallic iron-organic coordination compounds... 

Masset and coworkers studied the thermal decomposition of FeS04-6H20 by MS coupled with DTA-TG under an inert atmosphere. The TG measurements suggest that the mechanism of decomposition of FeS04 6H20 can be divided into i) three dehydration steps ... 

The main tbermal analysis technique with which EGA has been coupled it IhertnogravimeUy (TG) and simultaneous lechniqucs (sec Chapter 7) are usually indicated by byphenaiiiw, for example TG-MS or TG-FTIR,... 

The gaseous products evolved during a TG measurement are a rich source of information and these gases are readily analysed by coupling an appropriate instrument to the TG apparatus. This form of thermal analysis is often referred to as evolved gas analysis (EGA), and is discussed in Section 6.1. Mass spectrometers (TG-MS), Fourier transform infrared spectrometers (TG-FTIR) and gas chromatographs (TG-GC) may be coupled for simultaneous TG-EGA. 

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