Thermally assisted hydrolysis and methylation - a simple and rapid online derivatization method for the gas chromatographic analysis of natural waxes

Thermally assisted hydrolysis and methylation (THM) provides an interesting alternative to other derivatizing sample preparation techniques because of its simplicity and rapidness. The paper presents THM-GC/MS data obtained f rom standard compounds (cholesteryl stearate, 2-hydroxypalmitic acid) and s everal types of wax (candelilla wax, beer wax, lanolin, beeswax) using tetr amethylammonium. hydroxide (TMAH) as reagent. Application of tetramethylamm onium acetate (TMAAc) instead of TMAH enables selective analysis of free fa tty acids in the presence of esters. Comparison of the results with those o btained from Py-GC/MS illustrates that THM provides a much higher extent of information. The thermochemolytic behaviour of several wax compounds is di scussed. THM yields may differ from compound to compound due to specific th ermal and chemical behaviour. While structurally simple wax esters, e.g. ch olesteryl stearate, gave very efficient conversion within a wide temperatur e range between 350 and 600 degreesC, compounds of less thermal stability ( e.g. 2-hydroxyfatty acids) yielded substantial amounts of pyrolysis product s (aldehydes) even at the lowest temperature applied (350 degreesC). Some p hytosterols present in candelilla wax showed less affinity to TMAH and were only partly converted into methyl ethers. Various applications of THM-GC/MS are described: analysis of lipid based le ather polish, identification of wax content in spots in ancient Egyptian te xtiles, profiling of pharmaceutical lanolin batches, characterization of ag ing processes in lanolin. Fingerprints and characteristic marker compounds were employed for discrimination and identification purposes. (C) 2001 Else vier Science B.V. All rights reserved.