Off-line thermochemolysis-gas chromatography-mass spectrometry (GC-MS) using solid-phase microextraction (SPME) - phenolic acid analysis

Hilliard, Chastity (2001) Off-line thermochemolysis-gas chromatography-mass spectrometry (GC-MS) using solid-phase microextraction (SPME) - phenolic acid analysis. Masters thesis, Memorial University of Newfoundland.

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Abstract

An important class of compounds within the plant and animal kingdom are phenolic acids (i.e. hydroxy I substituted benzoic acids). Traditional methods used for the determination of these compounds are very time-consuming, involving procedures that include extraction, derivatization and finally GC analysis. An alternative method, called Pyrolysis/Methylation-GC (or thermochemolysis), applies the use of a derivatizing reagent, such as tetramethylammonium hydroxide (TMAH) for direct and rapid determination of these compounds in one analytical step. The polar functional groups (i.e. carboxylic and phenolic acid groups) are rapidly methylated and the products thermally desorbed onto the GC/MS column. Most analyses are on-line, where the pyrolysis unit is directly connected to the GC. However, there are serious drawbacks to on-line technique including the introduction ofthe methylating reagent onto the column and the requirement of a dedicated GC/MS. -- This study investigated method development for off-line thermochemolysis using solid-phase microextraction (SPME) for the analysis of phenolic acids using syringic acid as a model compound. The parameters investigated included pyrolysis temperature, SPME adsorption temperature and time, fibre size/phase, and split flow required for GC. Other thermochemolysis reagents investigated were tetramethylammonium acetate (TMAAc) and N,0-bis (trimethylsilyl) trifluoroacetamide (BSTFA). The effect of the solvent (i.e. methanol and water) used to dissolve the different reagents was also investigated. It was determined that aqueous TMAH was the most suitable reagent for phenolic acid analysis. The SPME off-line method was successfully optimized for highest quantity of methylated product. It was also determined that reagents BSTFA and TMAAc did not give reproducible results due to volatility of BSTFA and the insufficient basicity of TMAAc. -- The above method was applied to the analysis of phenolic acids present in white pine needles (Pinus strobus). Although most phenolic acids were successfully methylated, it was found that the SPME step was too selective as an extraction technique, that is, the phenolic acids observed in the chromatogram were dependent on the SPME adsorption temperature during headspace analysis. Future work should be focused on the use of SPME in aqueous solution of methylated products.

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