Identification of pyrolysis products

FI mass spectra were proven informative in algal polysaccharide analysis [2]. Characteristic Py-Fi mass spectra were reported for agarose, aiginic acid, laminaran, etc. Also, Py-GC/MS studies were done on algal polysaccharides [64a,64b]. The identification of pyrolysis products for several polysaccharides from red algae showed, as expected, compounds commonly obtained during polysaccharide pyrolysis. A list of several compounds found in these pyrolysates is shown in Table 7.8.2. 

Montaudo, G., Puglisi, C., Scamporrino, E., and Vitalini, D. Identification of Pyrolysis Products of Polysulfides by CAD-Linked Scanning Mass Spectrometry, /. Anal Appl Pyrolysis, 10, 283,1987. 

The identification of pyrolysis products and their sources in intact organisms was not widespread in pyrolysis studies until the last decade. Classification and differentiation of organisms were often based on the relative peak heights of one or more peaks at a given retention time in the pyrogram. This simplistic approach can lead to erroneous conclusions when the chemical identities of pyrolysis products and their origin are unknown. 

PyGC cannot be fully exploited for identification of unknown compounds in complex matrices, such as cured epoxy resins. It is impossible to identify unknown resins by pattern recognition. In those cases identification of pyrolysis products requires postchromatographic detection (MS, FTIR, AED) to collect structural information. 

From the above, some important features of pyrolysis GC-MS emerge, as given in Table 2.33. On-line flash pyrolysis GC-MS, with Curie-point, resistively-heated filament or furnace pyrolysers, is very widely utilised for identification of pyrolysis products from synthetic polymers. The main characteristics of PyGC-MS of polymers, as given by Schulten et al. [692], are shown in Table 2.34. PyGC-MS is an excellent tool for fast product quality control for R D purposes fiiU control of the (many) experimental parameters is needed. Polymer standards e.g. SEC standards) can be used to determine sensitivity and precision of PyGC-MS. 

Fig. 3.6. Automatic system for injection of sample into pyrolyser, pyrolysis and GC separation of pyrolysis products. For identification of components, see te. t. From ref. 69.

The residue of a thermal cracker (sample 18) seems to demonstrate losses only by distillation since the peak maxima were found in the temperature range 350-380 °C. Those temperatures are very low for a pyrolysis reaction, whereas the activation energy E = 172 kJ/Mole could represent a substance which is either easily crackable or tough volatile. The residue at 800 °C in thermogravimetry (/ 800 = 5.5 wt%) and the conversion in DSC V = 85.5 %) could result from either type of reaction. In this case it is a disadvantage that the instrument does not permit identification of the products formed. 

Information about the monomeric composition and structure can be obtained with pyrolysis MS but sequence information is lost [46]. The method was used in several applications, such as structural identification of homopolymers, differentiation of isomeric structures, copolymer composition and sequential analysis, identification of oligomers formed in the polymerization reactions, and identification of volatile additives contained in polymer samples [47]. One of the main challenges of the technique is the identification of the products in the spectrum of the multicomponent mixture produced by thermal degradation. 

Peak identification and retention data are given in Table 7.45 for a range of pyrolysis products. 

Py-GC-MS. The technique of pyrolysis-gas chromatography-mass spectrometry was used to definitively assign the weight loss peaks in TGA by identifying the decomposition products under an inert atmosphere. At least two different pyrolysis temperatures were used for each material in Table II (except for bentonite and TAP-bentonite). In this fashion, isolation and identification of the products evolved during at least two major TGA transitions was possible. Thus, TMPyPCl was pyrolyzed at 420 C and 600 C to determine transitions B and C (by subtraction), respectively transition A is known to be due to water. The temperatures of pyrolysis for all samples are summarized in Table III, along with product assignments. The terms "pyridines" and "anilines" in... 

The main problem connected with direct pyrolysis technique is the identification of the products in the spectrum produced by the thermal degradation. In fact, in the mass spectrum of a polymer, the molecular ions of the thermal products will appear mixed with the fragment ions formed in the ionizing step. 

Chopra NM, Campbell BS, Hurley JC. 1978. Systematic studies on the breakdown of endosulfan in tobacco smokes Isolation and identification of the degradation products from the pyrolysis of endosulfan I in a nitrogen atmosphere. J Agric Food Chem 26 255-258. 

Fast screening techniques, such as temperature-resolved in-source filament pyrolysis and laser-assisted pyrolysis, benefit from the high cycle time and mass accuracy of FUCR-MS [214]. An additional advantage of FUCR-MS in the study of pyrolysis processes is that MS can be readily used for structural identification of desorption and pyrolysis products. 

In direct insertion techniques, reproducibility is the main obstacle in developing a reliable analytical technique. One of the many variables to take into account is sample shape. A compact sample with minimal surface area is ideal [64]. Direct mass-spectrometric characterisation in the direct insertion probe is not very quantitative, and, even under optimised conditions, mass discrimination in the analysis of polydisperse polymers and specific oligomer discrimination may occur. For nonvolatile additives that do not evaporate up to 350 °C, direct quantitative analysis by thermal desorption is not possible (e.g. Hostanox 03, MW 794). Good quantitation is also prevented by contamination of the ion source by pyrolysis products of the polymeric matrix. For polymer-based calibration standards, the homogeneity of the samples is of great importance. Hyphenated techniques such as LC-ESI-ToFMS and LC-MALDI-ToFMS have been developed for polymer analyses in which the reliable quantitative features of LC are combined with the identification power and structure analysis of MS. 

Most dyes, including sulfonated azo dyes, are nonvolatile or thermally unstable, and therefore are not amenable to GC or gas-phase ionisation processes. Therefore, GC-MS techniques cannot be used. GC-MS and TGA were applied for the identification of acrylated polyurethanes in coatings on optical fibres [295]. Although GC-MS is not suited for the analysis of polymers, the technique can be used for the study of the products of pyrolysis in air, e.g. related to smoke behaviour of CPVC/ABS and PVC/ABS blends [263],... 

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