Thermally assisted hydrolysis and methylation

Instead of the wet chemical hydrolysis and derivatization before GC/MS analysis, methods based on pyrolysis-GC/MS with in situ thermally assisted hydrolysis and methylation or silylation can be used, as described in detail in Chapters 11 and 12. 

J.M. Challinor, Review the Development and Applications of Thermally Assisted Hydrolysis and Methylation Reactions, Journal of Analytical and Applied Pyrolysis, 61, 3 34 (2001). 

Y. Ishida, S. Wakamatsu, H. Yokoi, H. Ontani and S. Tsurge, Compositional analysis of polyunsaturated fatty acid oil by one step thermally assisted hydrolysis and methylation in the presence of trimethylsulfonium hydroxide, J. Anal. Appl. Pyrol., 49, 267 276 (1999). 

F. Cappitelli, T. Learner and O. Chiantore, An initial assessment of thermally assisted hydrolysis and methylation gas chromatography/mass spectrometry for the identification of oils from dried paint films, J. Anal. Appl. Pyrol., 63, 339 348 (2002). 

A. Asperger, W. Engewald and G. Fabian, Thermally assisted hydrolysis and methylation a simple and rapid on line derivatization method for gas chromatographic analysis of natural waxes, J. Anal. Appl. Pyrol., 61, 91 109 (2001). 

Gamier, N., Richardin, P., Cheynier, V. and Regert, M. (2003). Characterization of thermally assisted hydrolysis and methylation products of polyphenols from modern and archaeological vine derivatives using gas chromatography-mass spectrometry. Analytica Chimica Acta 493 137-157. 

TMS production involves one specific functional group (-OH, -COOH, =NH, -NH2, or -SH), which loses an activated hydrogen and is replaced by a trimethylsilyl group (Proestos et ah, 2006). To achieve silylation, some authors have used BSTFA (N,0-hA(trimethyl-silyl)trifluoroacetamide) and TMCS (trimethylchlorosilane) successfully in several matrices (e.g. aromatic plants, cranberry fixiit) (Zuo et ah, 2002 Proestos et ah, 2006). Using silylated derivatives is advantageous for several reasons phenols and carboxylic acids are prone to silylation, these compounds can be derivatized in the same part of the process, and the minor products do not impede analysis and are well documented (Little, 1999 Stalikas, 2008). A two-step methylation procedure was used to analyze catechins and tannins in plant extracts. The first step used trimethylsilyl diazomethane (TMS-diazomethane) to pre-methylate the sample, and the second step used thermally assisted hydrolysis and methylation (THM). The pre-methylation step with TMS-diazomethane stabilized the dimer molecule m/z 540) by minimizing isomerization and reducing reactivity. (Shadkami et ah, 2009). 

Pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) at a lower temperature of 300° C was studied for both PES and PSF [11]. In this study, the main component for the thermally assisted hydrolysis and methylation of PES was dimethyl derivative of bis(4-hydroxyphenyl)sulfone. This compound was formed through selective cleavages of ether linkages maintaining intact the sulfone structures. For PSF thermally assisted hydrolysis and methylation at 300° C, the main constituents were dimethyl derivative of bis(4-hydroxyphenyl)isopropylidene (bisphenol A) and also dimethyl derivative of bis(4-hydroxyphenyl)sulfone. A partial decomposition of the sulfone groups in PSF during the THM reaction also was noted. The findings also were confirmed by matrix assisted laser desorption mass spectrometric measurements. 

Saiz-Jimenez, C. and Hermosin, B., Thermally assisted hydrolysis and methylation of dissolved organic matter in dripping water from Altamira cave, J. Anal. Appl. Pyrolysis, 49, 337-347, 1999. 

CappiteUi, R, T. Learner, and A. Cummings, Thermally assisted hydrolysis and methylation-gas chromatography/mass spectrometry for the chemical characterization of traditional and synthetic binders, in ICOM Committee for Conservation, 13th Triennial Meeting, Rio de Janeiro, September 22-27, 2002, pp. 231-237. 

Kaal, E. de Koning, S. Brudin, S. Janssen, H.G. Fully automated system for the gas chromatographic characterization of polar biopol3miers based on thermally assisted hydrolysis and methylation. J. Chromatogr. A, 2008,1201, 169-175. 

Riedo, C., Scalarone, D., Chiantore, O. (2010) Advances in identification ot plant gums in cultural heritage by thermally assisted hydrolysis and methylation. Analytical and Bioanalytical Chemistry, 396,1559-1569. 

Buurman, R, K. G. J. Nierop, J. Kaal, and N. Senesi. 2009. Analytical pyrolysis and thermally assisted hydrolysis and methylation of EUROSOIL humic acid samples—A key to their source. Geoderma 150, no. 1-2 10-22. 

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. 

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. 

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