The activity of nanopowder and mesoporous titanium catalysts for the analysis of fatty acids in triglycerides by pyrolysis methylation with dimethyl carbonate

The activity of Ti doped MCM-41 mesoporous materials towards pyrolysis transmethylation of triglycerides with dimethyl carbonate (DMC) was compared to that of titanium silicate and titanium oxide nanopowders. DMC solutions of soybean oil, utilised as test lipid material, were pyrolysed in the presence of few milligrams of active solids under off-line and on-line (Py-GC-MS) conditions. While the yields of fatty acid methyl esters (FAMEs) determined by off-line pyrolysis were negligible with undoped MCM-41, those of Ti-MCM-41 increased with increasing Ti content from 3.5% (at Ti/Si molar ratio 1/28) to 17% at Ti/Si molar ratio 1/9 becoming comparable to those of titanium silicate nanopowders (13%). Titania nanoparticles enriched in rutile or anatase were the most active solids (19-26%), while coarse TiO2 (NIST) was poorly active (0.7%). The best performing Ti-MCM-41 was more effective than nanopowder titanium silicate for profiling FAMEs by on-line Py-GC-MS, but caused a larger double bond isomerisation of linoleic acid with respect to TiO2 nanopowders. Although the accuracy of pyrolysis/methylation with DMC and Ti-MCM-41 was inferior to standard methods, the method is appealing in the field of green analytical chemistry for being essentially a simple one-step procedure utilising small quantity of non-toxic and non-corrosive reagents. The method was tested on real matrices using DMC to extract the lipid fraction and was further explored by preparative pyrolysis with a fixed bed reactor. (C) 2008 Elsevier B.V. All rights reserved.