Thermal-decomposition analytical

A two-step laboratory thermal-decomposition analytical system involving vaporization and thermal destruction was developed in 1975 by the University of Dayton Research Institute for EPA (6). Vaporization of pure pesticide occurred at 200 to 300°C and was followed by decomposition in a quartz tube at temperatures exceeding 900 C. The destruction efficiencies for DDT, Kepone, and mirex exceeded 99.99% at 2-s residence time and greater than 900 C. 

Of the many molybdenum sulfides which have been reported, only MoS, M0S2 and M02S3 are well established. A hydrated form of the trisulfide of somewhat variable composition is precipitated from aqueous molybdate solutions by H2S in classical analytical separations of molybdenum, but it is best prepared by thermal decomposition of the thiomolybdate, (NH4)2MoS4. MoS is formed by heating the calculated amounts of Mo and S in an evacuated tube. The black M0S2, however, is the most stable sulfide and, besides being the principal ore of Mo,... 

Analytical procedures sensitive to 2 ppm for styrene and 0.05 ppm or less for other items were used for examining the extracts. Even under these exaggerated exposure conditions no detectable levels of the monomers, of the polymer, or of other potential residuals were observed. The materials are truly non-food-additive by the FDA definitions. Hydrogen cyanide was included in the list of substances for analysis since it can be present at low levels in commercial acrylonitrile monomer, and it has been reported as a thermal decomposition product of acrylonitrile polymers. As shown here, it is not detectable in extracts by tests sensitive to... 

Decomposition of some thermally labile analytes is observed. 

Recommendation Dilute the standard solutions twice with blank solutions prepared from each of the blank samples. Impurities in the blank samples reduce the thermal decomposition of the target analytes in the injection port and stabilize the profiles of ionization and fragmentation of the target analytes. 

Flow limitations restrict application of the DFI interface for pSFC-MS coupling. pSFC-DFI-MS with electron-capture negative ionisation (ECNI) has been reported [421], The flow-rate of eluent associated with pSFC (either analytical scale - 4.6 mm i.d. - or microbore scale 1-2 mm, i.d.) renders this technique more compatible with other LC-MS interfaces, notably TSP and PB. There are few reports on workable pSFC-TSP-MS couplings that have solved real analytical problems. Two interfaces have been used for pSFC-EI-MS the moving-belt (MB) [422] and particle-beam (PB) interfaces [408]. pSFC-MB-MS suffers from mechanical complexity of the interface decomposition of thermally labile analytes problems with quantitative transfer of nonvolatile analytes and poor sensitivity (low ng range). The PB interface is mechanically simpler but requires complex optimisation and poor mass transfer to the ion source results in a limited sensitivity. Table 7.39 lists the main characteristics of pSFC-PB-MS. Jedrzejewski... 

Direct liquid injection (DLI) has been used even less. Hirter et al. [579] have reported the early analysis of a synthetic antioxidant mixture (Irganox 1010/1076/1098) by means of iRPLC-DLI-QMS with Cl. In early studies, the HPLC effluent was vaporised by laser radiation [593] both El and solvent-mediated Cl spectra were obtained in the on-line mode from analytically difficult molecules. However, the instrumentation was complex the sensitivity was not as good as that obtained by GC-MS and thermal decomposition was observed with other compounds. This direct introduction approach with enrichment was used for the analysis of phthalates. 

Rondevstedt, C. S., Chem. Eng. News, 1977, 55(27), 38 Synthesis, 1977, 851-852 In an attempt to reduce 2-chloro-5-methylnitrobenzene to the aniline by treatment with excess hydrazine and Pd/C catalyst, the hydroxylamine was unexpectedly produced as major product. During isolation of the product, after removal of solvent it was heated to 120°C under vacuum and exploded fairly violently. Many aryl-hydroxylamines decompose violently when heated above 90-100°C, especially in presence of acids. GLC is not suitable as an analytical diagnostic for arylhydroxyl-amines because of this thermal decomposition. 

It has been suggested however that isotacticity derives from polymerization occurring on colloidal particles formed by thermal decomposition of the catalysts. As stated previously, in the presence of the monomer even the allyl compounds are stable at 65°C and none of the thermal decomposition products (black to yellow solids) could be detected. As a check on these results a polymerization of propylene was carried out with Zr (benzyl) 4 in toluene at 0°C in a sealed tube. The reaction was very slow and analytical quantities of polymer could be obtained only after 312 hr. NMR analysis showed peaks assignable to isotactic sequences, and these were much stronger than the peaks assignable to syndiotactic diads. It was concluded... 

However, pyrolysis is rapid, avoids sample wet chemical workup, avoiding sample loss and contamination, and has a low sample requirement. It allows the determination, in a single step, of polymeric materials (with in situ hydrolysis of the hydrolysable polymers and thermal decomposition of the nonhydrolysable polymers) and low molecular weight components [16]. As a result, pyrolysis is a relatively fast and inexpensive technique, especially if compared with the classical wet analytical procedures that are required prior to GC/MS analyses. 

Spectroscopic developments have accelerated advances in the field of catalysis. This volume analyzes the impact on catalyst structure and reactivity of EXAFS, SIMS, MSssbauer, magic-angle spinning NMR (MASNMR), and electron-energy-loss vibrational spectroscopy. Many of these techniques are combined with other analytical tools such as thermal decomposition and temperature-programmed reactions. 

The high water-solubility of surfactants and their, often more polar, metabolites prevents direct application of gas chromatographic separation (GC) with appropriate detection. The necessary volatilisation without thermal decomposition can be achieved by derivatisation of the analytes, but these manipulations are time- and manpower-consuming and can be susceptible to discrimination. Additionally, each derivatisation step in environmental analysis is normally target-directed to produce volatile derivatives of the compounds to be determined. Unknown surfactants that are simultaneously present, but differ in structure and therefore cannot react with the derivatisation reagent, are discriminated under these conditions. 

In either case, the use of a DEP allows to extend the temperature range for evaporation. In addition, it reduces thermal degradation as a result of heating the analyte faster than its thermal decomposition usually proceeds, and therefore expands the range of applications for El and Cl to some extent. Whatsoever, employing direct exposure probes is by far no replacement of real desorption ionization methods. [52,53]... 

Classical organic chemistry provides a wide variety of potential analytes for electron ionization, the only limitation being that the analyte should be accessible to evaporation or sublimation without significant thermal decomposition. These requirements are usually met by saturated and unsaturated aliphatic and aromatic hydrocarbons and their derivatives such as halides, ethers, acids, esters, amines, amides etc. Heterocycles generally yield useful El spectra, and flavones, steroids, terpenes and comparable compounds can successfully be analyzed by El, too. Therefore, El represents the standard method for such kind of samples. 

The molecular ion peak directly provides valuable information on the analyte. Provided the peak being of sufficient intensity, in addition to mere molecular mass, the accurate mass can reveal the molecular formula of the analyte, and the isotopic pattern may be used to derive limits of elemental composition (Chaps. 3.2 and 3.3). Unfortunately, the peak of highest m/z in a mass spectrum must not necessarily represent the molecular ion of the analyte. This is often the case with El spectra either as a result of rapidly fragmenting molecular ions or due to thermal decomposition of the sample (Chaps. 6.9 and 6.10.3)... 

---