Detecting the presence and amounts of aroma compounds in olive, sunflower, fish, and other edible oils is important for product manufacturers and vendors. Off flavors that originate from degradation of such unsaturated fatty acids as hexanal, 2-nonenal and 2,4-decadienal can compromise taste and therefore product quality. These effects can occur in low (ng/g) concentrations. Therefore, fast and sensitive analysis, with simple sample preparation, has typically been necessary.
GERSTEL developed a simple method that requires no sample preparation to address this type of analysis. It was found that direct thermal desorption of samples placed in microvials using a Thermal Desorption Unit (TDU) performed satisfactorily for volatile analytes, but was not as sensitive for determining high-boiling compounds, like 2,4-decadienal. GERSTEL scientists looked at different forms of microvial design and tested five different versions to improve the transfer of high boiling compounds while maintaining high sensitivity for volatile samples.
The microvials tested were standard (with a single notch) or had a slit or cut in the vial’s side. One version had a slit 1.5 cm from the bottom, another with a slit at 1 cm from the bottom. In turn, the cut vials had a cut at 1.5 cm or 1 cm from the bottom. Oil samples were placed in each microvial and thermally desorbed using the GERSTEL TDU. The TDU was mounted on a Cooled Injection System, PTV-type inlet which acts a refocussing trap. Analyte separation and detection were performed using an Agilent Technologies 7890/5975 GC/MS.
For testing, the edible oils were spiked with analytes, with a concentration range between 10 and 1,000 ng/g. About 13 compounds were spiked; these included hexanal, methional, 2-nonenal, 2,4-nonadienal, and 2,4-decadienal.
The use of microvials prevented contamination of the analysis system by high boiling matrix compounds, and allowed efficient transfer of analytes onto the analytical column. The study found that microvials with a slit placed 1 cm from the bottom worked best at transferring analytes to the column. This advantage was particularly noticeable for high boiling compounds.
The slit design (and placement) allowed for faster and more efficient transfer, and introduction of liquid samples to the microvials was easily performed with a pipette, representing the only sample preparation step. The 1 cm slit microvial is now commercially available from GERSTEL, as well as its traditional microvials.
You can learn more about this experiment, and see SIM chromatograms, comparative peak areas of the different microvial designs, and more by reading our application note, entitled “Analysis of Aroma Compounds in Edible Oils by Direct Thermal Desorption of GC/MS using Slitted Microvials.”
For a deeper conversation about how the new slit microvials and Thermal Desorption Unit can aid in your aroma compound analysis, feel free to contact us.