Pyrolysis-derivatisation

J.M. Challinor, A pyrolysis derivatisation gas chromatography technique for the structural elucidation of some synthetic polymers, J. Anal. Appl. Pyrol., 16, 323 333 (1989). 

The composition and microstracture of polymers in a latex system were studied by pyrolysis gas chromatography. The composition and microstructure of a polymer in the emulsion phase were identified by direct pyrolysis of the latex system, followed by comparing the trimer peak pattern with appropriate microstructure standards. The polymer in the aqueous phase was pre-pyrolysis derivatised with tetrabutylammonium hydroxide to convert the acid to its butyl ester. Similar procedures were then used to explore the composition and microstructure of the polymer in the aqueous phase. Polymers analysed included SCX-2660 (probably a styrene-methyl methacrylate-butyl acrylate terpolymer), styrene-butyl acrylate copolymer and styrene-alpha-methylstyrene-butyl acrylate terpolymer. 17 refs. 

Thermally-assisted hydrolysis and methylation (THM) using organic alkaline reagents is widely utilised for reliable and informative characterisation of various condensation-type polymers that are often intractable for the conventional pyrolysis techniques [619]. Wang [618] has extended the derivatisation concept and distinguishes pre-pyrolysis and post-pyrolysis (i.e. pre-column ) derivatisation reactions. The purpose of pre-pyrolysis derivatisation is to secure a favourable thermal degradation pathway during pyrolysis. 

Challinor [611,620] has reported the use of pyrolysis derivatisation techniques, simultaneous pyrolysis methylation (SPM), cq. THM. In Py-THM-GC the sample (about 5 /xg) is typically placed in the hollow of a flattened Curie-point pyrolysis wire with approximately 0.5 /u-L tetramethyl ammonium hydroxide (TMAH) (25 wt.% aqueous solution) or tetramethylsulfonium hydroxide (TMSH). The prepared wire is then immediately located in the py-rolyser without allowing aqueous TMAH to evaporate and pyrolysis is carried out at the predetermined temperature. Special injectors for chemolysis (e.g. PTV injector) allow THM also for furnace PyGC experiments. Moldoveanu [499] has listed other common derivatisations utilised in GC analysis. 

Vegetable oils and fats are usually identified as their fatty acid derivatives or their triglycerides. The well-established methods usually depend on GC as a means of identification. Pyrolysis derivatisation procedures (THM-GC) developed more recently [636] provide a method for characterising these materials. Microgram quantities of the triglycerides are reacted with tetramethylammonium hydroxide (TMAH) at high temperature to yield fatty acid methyl esters without employing multistep procedures. 

Simultaneous pyrolysis-derivatisation the presence of a suitable reagent followed by immediate analysis by suitable techniques (see Section 5.2). 

Gamma, of a photographic emulsion 769 Gas chromatography 235 apparatus for, 235 column packing for, 238 derivatisation in, 236 detectors for, 240 elemental analysis by, 247 of metal chelates 237, 248 pyrolysis, 237... 

Nonvolatile compounds cannot be analysed unless pyrolysis or derivatisation converts them to a condition amenable to GC. Derivatisation GC (or LC) has been used for several components such as erucamide (imidi-sation for volatility), fatty amines (aromatic amidation for UV detectability), and polyethylene oxides (esterification for both volatility and detectability) [178]. The surface concentration of erucamide on extruded LLDPE films was determined quantitatively by surface washings with ether, followed by evaporation, dissolution... 

A deactivated silica pre-column is also a fundamental tool when pyrolysis is performed, since it partially helps in avoiding the contamination of the analytical column with underivatised polar compounds. Blanks (that is the pyrolysis of the derivatising agent without sample) must be run between analyses to ensure the absence in the chromatograms of any signals that do not belong to the sample. 

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 ... 

The pyrolysis of glycerolipid materials requires the use of a suitable derivatising agent, in order to increase the detectability of fatty acids and dicarboxylic acids, which may be present in a mature paint film as free acids, metal soaps, as well as esterified with glycerol. The oils and fats commonly used in samples from works of art have been analysed by means of pyrolysis using TMAH [12,23,25,26,32 38], and HMDS [37,39]. 

To demonstrate these aspects, the different pyrograms obtained from the pyrolysis of aged linseed oil samples using different derivatising agents and different pyrolysers are shown. 

The inorganic materials are sometimes even capable of hindering derivatisation, as shown in the chromatogram of Figure 11.4, which was obtained from a mature linseed oil paint sample containing high amounts of sulfates only underivatised acids are observed. The pyrolyser was a CDS Pyroprobe 5000 series (CDS Analytical Inc, Oxford, USA) pyrolyser interface 180°C transfer line 300°C valve oven 290°C. Pyrolysis was performed in the presence of HMDS at 600°C. 

Fresh plant resins have been characterised by means of pyrolysis coupled to GC/MS without the use of a derivatising agent. However, many markers used for the identification of resins in samples from works of art are often not cogent, and moreover they disappear during ageing [42]. 

Processing the polymer 9.16 followed by pyrolysis provides an excellent method for preparing this valuable ceramic in shaped forms such as fibres and monoliths. Derivatisation of 9.16 by a thermal dehydrocoupling reaction with amines NHR2 to replace -H substituents on boron by -NR2 groups can be achieved.Examples of void-free BN fibres prepared from polyaminoborazylene precursors formed by... 

Piccirillo, A., Scalarone, D., Chiantore, O. Comparison between off-hne and on-line derivatisation methods in the characterisation of siccative oils in paint media. Journal of Analytical and Applied Pyrolysis, 74, 2005, 33-38. 

Wang and co-workers [146] have pointed out that low levels of monomers can only be approached by pyrolysis/trapping techniques but can also achieved by derivatisation. An example is quoted of the determination of fumaric acid and itaconic acid in emulsions by pyrolysis-GC in which these acids are reacted with methylamine to form cyclic iodine type functional groups. The derivatisation products produce a stable pyrolysate which can be detected at low concentrations. 

Wang and co-workers [6] used a Py-GC technique for the qualitative analysis of fumaric acid and itaconic acid as low-level monomers polymerised with other major monomers in emulsion styrene maleic anhydride co-polymers. In order for fumaric acid and itaconic acid to be detected through pyrolysis, the acids are derivatised with primary amines such as methylamine and ethylamine to form a cyclic imide. The detection of derivatised fumaric acid and itaconic acid was accomplished by atomic emission detection. The structures of the derivatisation-pyrolysis products were elucidated by MS. 

Thermally-assisted hydrolysis and methylation Although GC separation facilitates identification of the pyrolysate, it prevents detection of certain pyrolysis products, notably polar and high-boiling compounds, which contain particularly useful diagnostic information about the structure of a material. In conventional GC this problem may be remedied by derivatisation of the polar compounds externally or by co-injection to give compounds which may be efficiently separated. Similarly, in order to realise the full potential of on-line PyGC high-temperature in situ derivatisation reactions may be carried out. 

Prepyrolysis/derivatisation in which the functional groups of the polymer are reacted with a suitable reagent to obtain a favourable thermal decomposition pathway followed by examination by pyrolysis and other suitable techniques. The main difference between prepyrolysis derivatisation and postpyrolysis derivatisation is that the polymer backbone should be stable enough to resist the attack from the derivatisation reagent in prepyrolysis derivatisation (see Section 5.3). 

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