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 from standard compounds (cholesteryl stearate, 2-hydroxypalmitic acid) and several types of wax (candelilla wax, beer wax, lanolin, beeswax) using tetramethylammonium. hydroxide (TMAH) as reagent. Application of tetramethylammonium acetate (TMAAc) instead of TMAH enables selective analysis of free fatty acids in the presence of esters. Comparison of the results with those obtained from Py-GC/MS illustrates that THM provides a much higher extent of information. The thermochemolytic behaviour of several wax compounds is discussed. THM yields may differ from compound to compound due to specific thermal and chemical behaviour. While structurally simple wax esters, e.g. cholesteryl stearate, gave very efficient conversion within a wide temperature range between 350 and 600 degreesC, compounds of less thermal stability (e.g. 2-hydroxyfatty acids) yielded substantial amounts of pyrolysis products (aldehydes) even at the lowest temperature applied (350 degreesC). Some phytosterols 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 leather polish, identification of wax content in spots in ancient Egyptian textiles, profiling of pharmaceutical lanolin batches, characterization of aging processes in lanolin. Fingerprints and characteristic marker compounds were employed for discrimination and identification purposes. (C) 2001 Elsevier Science B.V. All rights reserved.