Pyrolysis instrument

A sensitive and selective chemiluminescent detector that has made an appreciable impact on the analysis of nitrosamines in environmental samples in the last several years is the thermal energy analyzer or (TEA) (15-19). This detector utilizes an initial pyrolysis reaction that cleaves nitrosamines at the N-NO bond to produce nitric oxide. Although earlier instrumentation involved the use of a catalytic pyrolysis chamber (15,17,19), in current instruments, pyrolysis takes place in a heated quartz tube without a catalyst (20). The nitric oxide is then detected by its chemiluminescent ion react with ozone. The sequence of reactions can be depicted in Figure 1. A schematic of the TEA is shown in Figure 2 (17). Samples are introduced into the pyrolysis chamber by direct injection or by interfacing the detector with a gas chromatograph (15,17,21,22) or a liquid chromatograph (22-25). 

Py/GC/MS. pyrolysis, gas chromatography, and mass spectrometry used as a combined technique Py/MS. pyrolysis and mass spectrometry used as a combined technique oa-TOF. orthogonally accelerated time of flight Q. quadrupole field or instrument... 

Mixtures can be identified with the help of computer software that subtracts the spectra of pure compounds from that of the sample. For complex mixtures, fractionation may be needed as part of the analysis. Commercial instmments are available that combine ftir, as a detector, with a separation technique such as gas chromatography (gc), high performance Hquid chromatography (hplc), or supercritical fluid chromatography (96,97). Instmments such as gc/ftir are often termed hyphenated instmments (98). Pyrolyzer (99) and thermogravimetric analysis (tga) instmmentation can also be combined with ftir for monitoring pyrolysis and oxidation processes (100) (see Analytical methods, hyphenated instruments). 

Conventional rubber compound analysis requires several instrumental techniques, in addition to considerable pretreatment of the sample to isolate classes of components, before these selected tests can be definitive. Table 2.5 lists some general analytical tools. Spectroscopic methods such as FTIR and NMR often encounter difficulties in the analysis of vulcanised rubbers since they are insoluble and usually contain many kinds of additives such as a curing agent, plasticisers, stabilisers and fillers. Pyrolysis is advantageous for the practical analysis of insoluble polymeric materials. 

Pyrolysis spectra become distorted with respect to their diagnostic features for two major sets of reasons. The first is variations in instrument operation (e.g., heat transfer efficiency from wire to sample, ion source temperature, MAB gas identity, analyzer calibration, tuning, and ion transmission discrimination attributable to contaminated optics). Most of these factors can be controlled... 

With recent developments in analytical instrumentation these criteria are being increasingly fulfilled by physicochemical spectroscopic approaches, often referred to as whole-organism fingerprinting methods.910 Such methods involve the concurrent measurement of large numbers of spectral characters that together reflect the overall cell composition. Examples of the most popular methods used in the 20th century include pyrolysis mass spectrometry (PyMS),11,12 Fourier transform-infrared spectrometry (FT-IR), and UV resonance Raman spectroscopy.16,17 The PyMS technique... 

Results of pyrolysis mass spectrometric analyses can be influenced by both phenotypic drift and instrument drift. Phenotypic drift can result from variations in culture growth immediately prior to analysis, and from variations during serial subculturing before analysis.125,126 However, this type of drift is not perceived as an obstacle in microbiological work because it can be largely overcome by standardizing culture conditions and by analyzing more than one sample from each culture. 

Instrumental drift results from variations in the physical conditions of a pyrolysis mass spectrometer over time.127 It leads to variation in spectral fingerprints taken from the same material on different occasions. Short-term (<30 days) instrument reproducibility was examined by Manchester et al.57 who used PyMS to differentiate strains of Carnobacterium over a four-week period. Excellent reproducibility was obtained as separation of the five type strains was sustained and spectra did not change significantly over the four weeks. 

Shute, L. A. Gutteridge, C. S. Norris, J. R. Berkeley, R. C. W. Reproducibility of pyrolysis mass spectrometry effect of growth medium and instrument stability on the differentiation of selected Bacillus species. /. Appl. Bacteriol. 1988,64,79-88. 

The diversity of markers that are reported in the literature for the three proteinaceous binders, even when the same derivatising agent is used, highlights how several aspects come together to determine the final pyrolysis products. Animal glue for example, when pyrolysed at 600°C in the presence of HMDS, gives rise to different markers depending on the pyrolyser and instrumental set-up used ... 

For these reasons, when the pyrolysis of samples from works of art is undertaken for the first time, as well as when a new device or a new instrumental set-up is introduced in a laboratory, it is very important to build one s own libraries of chromatographic profiles, based on the analysis of reference materials. 

Fig. 2.1 Instrumental setup for screening analysis by evaporation/pyrolysis gas chromatography... 

EXMAT - A Linked Network of Expert Systems for Materials Analysis. Seven individual expert systems comprise EXMAT (1) problem definition and analytical strategy (2) instrumental configuration and conditions (3) data generation (4) chemometric/search algorithms (5) results (6) interpretation (7) analytical goals. Dynamic headspace (DHS)/GC and pyrolysis GC (PGC)/concentrators... 

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