Pyrolysis mass spectrum

An ANN is an array of three or more interconnected layers of cells called nodes (much like columns of cells in a spreadsheet). Data are introduced to the ANN through the nodes of the input layer. For instance, each input layer node can contain the relative intensity of one of the m/z values from a bacterial pyrolysis mass spectrum. The output layer nodes can be assigned to iden-... 

Fig. 5.2(A) presents the pyrolysis mass spectrum for the soil extract. In previous work (ref. 358,359,365) it was shown that complex organic materials like polysaccharides, proteins, lignins, and soil humic fractions have characteristic peaks yielding a typical pattern, which give preliminary information about the composition of the pyrolysis fragments. Thus, characteristic peaks for polysaccharides were observed at 60, 68, 82, 84, 96, 98, 110, 112, and 126 m/z, which were also present in the soil extract. They were shown to be related to acetic acid, furan, methylfuran, hydroxyfuran, furfural, furfuryl alcohol, methylfurfural, methoxy-methylfuran, and a typical pyrolysis fragment of polysaccharides with hexose and/or deoxyhexose units, respectively.

The introduction of non-volatile components into an MS has typically been via the pyrolysis of whole fermentation liquors. Pyrolysis is the thermal degradation of a material in an inert atmosphere or a vacuum. It causes molecules to cleave at their weakest points to produce smaller, volatile fragments called pyrolysate [23]. An MS can then be used to separate the components of the pyrolysate on the basis of their mass-to-charge ratio (m/z) to produce a pyrolysis mass spectrum, which can then be used as a chemical profile or fingerprint of the complex material analysed [24]. 

According to these equations the intensities in a pyrolysis mass spectrum can be divided into a number of contributions from different factors, possibly different chemical components [81, 82]. The intensity of a factor in a particular mass spectrum, called the factor score, can be obtained from rel. (53a or 53b). The coefficients Cj are a measure of the relative contribution of the individual factors to the intensities at a given m/z value. The factor scores of the first factor show the largest variation in the set of spectra [83, 84]. Score plots of one of the factors for each mass h (see rel. 53a) allow sometimes a differentiation of the masses with specific contribution from classes of compounds [85]. Also, scattered score plots of the first two discriminant factors may reveal... 

Py-MS is used to decrease sample preparation time for bacterial profiling. One method hydrolyzes and methylates fatty acids from bacteria without using chromatographic separation [87]. Figure 20.11 shows a pyrolysis-mass spectrum of fatty add methyl esters (fames) from four pathogenic bacteria. 

Voorhees KJ, Miketova P, Abbas-Hawks C, Hadfield TL. Identification of lipid-based biomarkers in the high-resolution pyrolysis/mass spectrum of Brucella neotomae. J Anal Appl Pyrolysis. 2006 75 33. 

Figure 10.6 (a) TIC curve, (b) pyrolysis mass spectrum at 445 °C and (c) single ion evolution profiles of some selected products detected during the pyrolysis of P2VP-b-PMMA. Reproduced from Ref [121] with kind permission of Elsevier. 

Figure 15 Pyrolysis mass spectrum of product ions of m/z 260 of phenylalanyl-leucine [Phe-Leu] (A) and a general fragmentation pathway of Phe-Leu and leucyl-phenylalanine [Leu-Phe] (B). Reproduced by permission of the American Society for Mass Spectrometry from Noguerola AS, Murugaveri B, Voorhees KJ (1992), Journal of the American Society for Mass Spectrometry 3 750-756.

Various methods of analysis exert different thermal stress on a material (Table 6.39). Direct heating in the inlet of a mass spectrometer in order to obtain a mass spectrum of the total pyrolysate is an example of thermochemical analysis. Mass spectrometry has been used quite extensively as a means of obtaining accurate information regarding breakdown products produced upon pyrolysis of polymers. Low residence times allow detection of high masses. 

Figure 5.5 Typical average pyrolysis Ar MAB/Tof mass spectrum from 0.5 pi, about 50,000 cells, of a tdh+ strain of V. parahaemolyticus serotype 04 K12.

As an example of the form of the information that may be derived from a pyrolysis-MS, Figure 26 [69] shows the structure of the polycarbonate (PC) and the EI-MS spectra of pyrolysis compounds obtained by DPMS of poly(bisphenol-A-carbonate) at three different probe temperatures corresponding to the three TIC (total ion current) maxima shown in Figure 27(b) Figure 27 compares the MS-TIC curve with those obtained from thermogravimetry. (The TIC trace is the sum of the relative abundances of all the ions in each mass spectrum plotted against the time (or number of scans) in a data collection sequence [70].)... 

The parent azocine (91) was isolated at —190 °C from flash vacuum pyrolysis of diazabas-ketene (90) (71JA3817). The compound, which must be handled in KOH-coated glassware, decomposes at -50 °C to colored tarry material. Characterization was by mass spectrum (m/e 107), NMR spectrum (see 91) and conversion with potassium in liquid ammonia to a dianion, which on quenching and hydrogenation gave azocane in low yield. 

In some polynuclear metal carbonyls of the first row (3d) transition metals the metal-metal bonds are too weak to survive complete loss of carbonyl groups. Thus in the mass spectrum of Fe3(CO)i2 stepwise loss of carbonyl groups occurs only as far as the tricarbonyltriiron ion Fe3(C0)s 2fl>. The rupture of the iron-iron bonds competes with the stepwise loss of carbonyl groups givingions such as Fe2(CO)4 and Fe(CO)4. The mass spectrum of Fe2(CO)9 exhibits the ion Fe(CO) which may represent pentacarbonyliron formed by the following pyrolysis process25) ... 

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