Injector-internal thermal desorption from edible oils. Part 1: visual experiments on sample deposition on the liner wall

Injector-internal thermal desorption from edible oils or fats enables the analysis of a wide range of compounds in oils or extracts of fatty food without prior removal of the sample matrix. The oil or fat is deposited onto the wall of the injector liner. The solutes of interest are evaporated, leaving behind the sample matrix. The injector is kept at a temperature volatilizing the solutes of interest, but minimizing evaporation of the bulk material of the oil. This technique was optimized regarding sample deposition on the liner wall (Part 1) and desorption of high boiling compounds, such as migrants from food packaging materials into simulant D (olive oil) or fatty food (Part 2). The sample liquid should be transferred to the liner wall and spread to a thin film in order to facilitate the release of high boiling components. Visual experiments with perylene-containing solutions showed that the oil must be diluted to reduce the viscosity (separation from the needle tip). The oil concentration should not exceed 20% in order to rule out that squirting sample liquid drops to the bottom of the vaporizing chamber. Further dilution to about 10% oil improves spreading of the liquid to a thin film. A rather high boiling solvent should be used, such as n-butyl acetate, to prevent thermospray at the needle exit and violent evaporation from the liner wall with sputtering liquid. Using a 5-mm ID liner, 5-10-microL injections of 10-20% oil solutions were at the upper limit.