Trimethylsulfonium hydroxide as derivatization reagent for the chemical investigation of drying oils in works of art by gas chromatography

A procedure for the determination of fatty acids (FA) and glycerol in oils has been developed. The method includes a derivatization step of the FAs into their methyl esters or a transesterification of the triacylglycerols with trimethylsulfonium hydroxide (TMSH), respectively. The analysis is carried out by gas chromatography with parallel flame ionization and mass spectrometric detection. The parameters involved in the transesterification reaction were optimized. Only the stoechiometric ratio of TMSH:total FA amount showed a significant influence on the reaction yield. Relative standard deviations for 10 replicates were below 3% for all FAs studied and their linearity range was 0.5–50 mmol/L, when using heptadecanoic acid as an internal standard. The final procedure was rapid and required little sample handling. It was then tested on fresh oil samples and presented satisfying results, in agreement with previous works.