Thermal analysis with mass spectrometry

The combination of thermal analysis with mass spectrometry represents one of the successful associations. 

Thermal properties of several chlorinated phenols and derivatives were studied by differential thermal analysis and mass spectrometry and in bulk reactions. Conditions which might facilitate the formation of stable dioxins were emphasized. No two chlorinated phenols behaved alike. For a given compound the decomposition temperature and rate as well as the product distribution varied considerably with reaction conditions. The phenols themselves seem to pyro-lyze under equilibrium conditions slowly above 250°C. For their alkali salts the onset of decomposition is sharp and around 350°C. The reaction itself is exothermic. Preliminary results indicate that heavy ions such as cupric ion may decrease the decomposition temperature. 

If the same variable parameter is used for two independent methods of analysis for the purpose of obtaining different information, in general a combination of the two techniques will provide a method which is more powerful than cither one taken alone. It is our purpose to show how a combination of thermal methods of analysis with mass spectrometry results in a single technique of exceptionally high significance (13). 

The combination of chromatography and mass spectrometry (MS) is a subject that has attracted much interest over the last forty years or so. The combination of gas chromatography (GC) with mass spectrometry (GC-MS) was first reported in 1958 and made available commercially in 1967. Since then, it has become increasingly utilized and is probably the most widely used hyphenated or tandem technique, as such combinations are often known. The acceptance of GC-MS as a routine technique has in no small part been due to the fact that interfaces have been available for both packed and capillary columns which allow the vast majority of compounds amenable to separation by gas chromatography to be transferred efficiently to the mass spectrometer. Compounds amenable to analysis by GC need to be both volatile, at the temperatures used to achieve separation, and thermally stable, i.e. the same requirements needed to produce mass spectra from an analyte using either electron (El) or chemical ionization (Cl) (see Chapter 3). In simple terms, therefore, virtually all compounds that pass through a GC column can be ionized and the full analytical capabilities of the mass spectrometer utilized. 

In an effort, to study the effect of introduction of -C=C- on thermal stability of polynitroaromatics, Feng and Boren designed 3,3 -bis((2,2, 4,4, 6,6 -hexanitrostilbene) and azo-3,3 -bis (2,2, 4,4, 6,6 -hexanitrostilbene), synthesized and studied their structural aspects by infrared (IR), NMR, elemental analysis and mass spectrometry [64]. These explosives are expected to have high m.p. and thermal stability in view of their large molecular masses and better molecular symmetry. Further, DSC study of these explosives also proves that thermal stability of an explosive is associated with its m.p. Also decomposition rate is accelerated... 

Spark source (SSMS) and thermal emission (TEMS) mass spectrometry are used to determine ppb to ppm quantities of elements in energy sources such as coal, fuel oil, and gasoline. Toxic metals—cadmium, mercury, lead, and zinc— may be determined by SSMS with an estimated precision of 5%, and metals which ionize thermally may be determined by TEMS with an estimated precision of 1% using the isotope dilution technique. An environmental study of the trace element balance from a coal-fired steam plant was done by SSMS using isotope dilution to determine the toxic metals and a general scan technique for 15 other elements using chemically determined iron as an internal standard. In addition, isotope dilution procedures for the analysis of lead in gasoline and uranium in coal and fly ash by TEMS are presented. 

The HPLC/MS technique used in EPA Method 8321 is best suited for analysis of thermally unstable compounds that are hard to analyze with conventional GC methods, such as organophosphorus pesticides, chlorinated herbicides, and carbamates. In this technique, the detection with mass spectrometry provides the ultimate selectivity. The sensitivity for each individual compound depends on the interferences in a given environmental matrix and on the chemical nature of the analyte. 

Lewisite 1 per se is never found in the environment. Figure 18 shows that this compound hydrolyzes rapidly on contact with moisture to 2-chlorovinyl arsonous acid, which in turn slowly dehydrates to lewisite oxide (syn. 2-chlorovinyl arsenous oxide) (16). Both 2-chlorovinyl arsonous acid and lewisite oxide are nonvolatile. The most frequently used method for the identification of CWC-related chemicals is based on gas chromatography (GC) in combination with mass spectrometry (GC/MS). Indirect GC/MS analysis of lewisite 1 requires sample preparation, which involves conversion of lewisite oxide to 2-chlorovinyl arsonous acid in an acidic environment, followed by derivatization (12). The obtained species is both volatile and thermally stable, and thus amenable to GC analysis. Often, a mercaptan reagent is used as a derivatization agent. The reaction with 3,4-dimercaptotoluene is shown in Figure 19. 

The coupling of liquid chromatography (LC) with mass spectrometry (MS) has undergone much evolution since its initial inception [1,2], Atmospheric pressure ionization techniques such as electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) opened the door for the ionization and analysis of nonvolatile or thermally labile analytes. This technique revolutionized drug discovery and development allowing for dramatic improvements in sensitivity, selectivity, and speed. This area continues to grow, and significant advances have been and continue to be achieved in all three areas [3-5],... 

Since all polymeric intermediates, and in many instances also the final ceramics, are amorphous, only thermal and spectroscopic methods can be utilized to characterize the thermal conversion. The most extensive studies have been performed on the polymer N-methylpolyborosileizane (PBS-Me), made from the single source precursor TADB. The pyrolysis has been monitored in situ by differential thermal analysis combined with thermo-gravimetric analysis and mass spectrometry (DTA/TG/MS). For ex situ investigations, batches of the polymer were treated at different temperatures, cooled to room temperature, and characterized by infrared spectroscopy and nuclear magnetic resonance spectroscopy. 

Quantitative analysis is performed primarily with an online combination of a chromatographic separation device with mass spectrometry. For example, GC/MS is used for small, thermally stable, relatively volatile compounds, and LC/MS for nonvolatile compounds. MALDI-MS can also be used to quantify nonvolatile compounds. 

Isobar can be a source of positive bias in the determination of Pu isotopic abundance by mass spectrometry despite prior chemical separation of the two elements. In this respect, eluting Pu before U is advantageous (see section Isotopic Analysis by Thermal Ionization Mass Spectrometry, procedures (b)-(d)). Great attention must be placed anyway to minimize sources of blanks due to low levels of natural uranium in most chemical reagents and mass spectrometry filaments. It is therefore still customary to perform Pu measurement by alpha spectrometry in parallel with mass spectrometry. 

Fiedler R (1995) Total evaporation measurements experience with multi-collector instruments and a thermal ionization quadrupole mass spectrometer. Int J Mass Spectrom Ion Processes 146-147 91-97 Fiedler R, Donohue D (1988) Pocket sensitivity calibration of multicollector mass spectrometers. In Symposium on trace dement analysis by mass spectrometry, Regensburg, 30 Sep 1987—2 Oct 1987 Fresenius Z Anal Chem 331(2) 209—213 Filippov VI, Moritz W, Terentjev AA, Vasiliev AA, Yakimov SS (2007) IEEE Sens J 7(2) 192-196 Fisher D (1997) History of the International Atomic Energy Agency, the first forty years, STI/PUB/1032, IAEA, Vienna... 

Reaction products were filtered by a 2-pm sintered ceramic element and sent to a Hewlett-Packard 6890 Gas Chromatograph (GC) with a thermal-conductivity detector (TCD). Combining gas chromatography with mass spectrometry (MS) allowed qualitative determination of several unknown product species. A Fimugan Mat 95 instrument was employed for the GC-MS product analysis. Nitrogen was the calibration gas for mass balances since it was an inert diluent in all experiments. The carbon and hydrogen balances typically closed to within 5%. The product selectivities were calculated on a carbon-atom basis. Carbon-atom selectivities are calculated as the ratio of the moles of a specific product to the total moles of all prrxlucts, scaled by the number of carbon atoms in the species. All data were reproduced on several catalysts with results consistent with those shown. 

A two-step degradation mechanism for pofycaprolactone has been proposed by Persenaire et al. [42], They studied thermal degradation of PCL by high resolution thermogravimetric analysis (TGA) simultaneously coupled with mass spectrometry (MS) arrd Forrrier transform infrared spectrometry (FTIR). Based on evolved gas analysis by both MS and FTIR it was concluded that the first step was a random rupture of polyester chains via cw-elimination reaction which produced H2O, CO2, and 5-hexanoic acid. The second step is an unzipping depolymerization process at the chain ends with hydroxyl end groups to form e-caprolactone (see Fig. 4.2). 

The methods discussed in this book are differential photocalorimetry, differential scanning calorimetry, dielectric thermal analysis, differential thermal analysis, dynamic mechanical analysis, evcrived gas analysis, gas chromatography, gas chromatography (oml)ined with mass spectrometry, mass spectrometry, microthermal analysis, thermal volalilisalion, Ihermogravimetric analysis and thermomechanical analysis. 

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