pass through a gas chromatographic column. , Less polar pyrolysis products such as alkanes and alkylbenzenes are thus detected and analyzed, but the more polar pyrolysis products of similar mass such as alcohols and carboxylic acids are not detected.

Derivatization of the sample renders many of these polar pyrolysis products sufficiently volatile for gas chromatographic separation. Thus it is possible to separate and detect many more structurally significant products than observed by conventional pyrolysis techniques.29,33 The most common of the derivatization processes is a methylation reaction where organic matter is mixed with tetramethylammonium hydroxide (TMAH) prior to pyrolysis. Throughout the literature, several different terms have been employed to describe derivatization reaction and in this chapter the term thermochemolysis will be used.

Thermochemolysis produces mostly long chain methyl esters and dimethyl esters via a mechanism which could first involve a pyrolysis to release an acid anion which is rapidly methylated in the gas phase or the TMAH may be saponifying/transesterifying long chain fatty acids esterified to a macromolecular network. This provides relatively good preservation of original carboxyl and hydroxyl structures in organic matter, due to formation of methyl-esters and methoxyls. Two processes, regarding functional groups, are clearly involved in the thermochemolysis of organic matter:

1. Partial decarboxylation of phenolic acids

2. Quantitative methylation of remaining carboxyls and partial methylation of hydroxyls

Presumably, as the pyrolysis cleaves polar fragments from organic matter, the TMAH methylates them in the chromatographic inlet, whereupon they undergo chromatographic separation. It is possible that the TMAH induces methylation of organic matter and this leads to higher product yields in the MS simply because charring or condensation reactions are minimized.

In practice, thermochemolysis of organic matter mainly produces esters of aliphatic and aromatic acids, methyl esters of aliphatic alcohols and phenols, and a variety of other methylated derivatization products.14 Thermochemolysis is particularly suitable for the analysis of fatty acids associated with organic matter matrix which are evolved as methyl esters when TMAH is employed.

Thermochemolysis enhances yields of pyrolysis products which are probably more

Was this article helpful?

0 0

Post a comment