Gas chromatographic separation and analysis of trimethylsilyl derivatives of some naturally occurring non-volatile phenolic compounds and related substances

Abstract

The gas-liquid chromatographic (GLC) separation of a group of naturally occurring phenolic compounds embracing benzaldehyde, benzoic acid, cinnamaldehyde, cinnamic acid, coumarin, flavone and isoflavone and/or derivatives has been studied. By using N,N-bis(trimethylsilyl)trifluoroacetamide as a silylating agent, a glass column packed with Chromosorb W AW DMCS (80–100 mesh) coated with 1.5% SE-30 + 1.5% SE-52 and a temperature program about thirty-six of the above substances could be separated in a single run. Using preparative GLC, together with a new collecting device, it was found that the yield of trimethylsilyl (TMS) 14C-labelled p-coumaric or ferulic acid was 81 to 85%. After hydrolysis of the collected radioactive TMS compounds it was further shown, via thin-layer chromatography and autoradiography, that only labelled p-coumaric or ferulic acid were present, indicating that little decomposition had occurred during GLC. In addition, ultraviolet, infrared, proton magnetic resonance and mass spectrometry were employed for studying the structures and conditions of the collected TMS derivatives from kaempferol, pyrocatechol and a series of phenolic acids. All the above analyses confirmed that the compounds were not appreciably altered during GLC. It is further suggested that preliminary multiple elimination thin-layer chromatographic separation and purification of eventually unknown phenolic substances from plant extracts, in combination with the described GLC technique and the employed physical methods, will be of great value for quantitative analysis and structure determination.