Comparison between off-line and on-line derivatisation methods in the characterisation of siccative oils in paint media

The characterisation of siccative oils (drying oils used in paint media) by gas-chromatography/mass-spectrometry using three derivatisation methods has been investigated and the differences in results discussed. The classic off-line derivatisation method with (trimethyl)silyldiazomethane has been compared with two alternative methods. The first involves on-line derivatisation using tetramethylammoniun hydroxide; in this case the reaction is performed in a pyrolysis interface at 600 °C. The second uses (m-trifluoromethylphenyl)trimethylammonium hydroxide as a derivatisation reagent (lower temperature required for methylation reaction without using the pyrolysis interface). The three methodologies have been found to give reproducible and comparable results for the different types of fresh and aged oils investigated.