Desorption Temperature, Solid-Phase Microextraction (SPME), and Natural Product Analyses, how Low Can we Go?

Solid phase microextraction (SPME) has become a common technique for volatile sampling due to its ease of use and limited technical requirements. The solvent-free nature of SPME is also exceptionally attractive for gas chromatography mass spectrometry (GC/MS) analysis. To ensure efficient transfer of the sample to the GC, the manufacturer recommend injector desorption temperatures in the range of 200 to 320 °C. A high desorption temperature can, however, have unwanted effects on analyses of plant and insect produced semiochemicals. By investigating the quantitative and qualitative chromatographic responses at varying inlet temperatures for a component blend of seven plant produced volatile compounds, we found the thermally labile plant-nematode signaling compound, pregeijerene to degrade to geijerene at all tested temperatures within the recommended range (200, 240, and 280 °C), but that it did not break down with an inlet temperature below 200 °C (100 °C and 150 °C). Degradation was also detected for the sesquiterpene germacrene D, but only at the highest inlet temperature tested (280 °C). Surprisingly, an inlet temperature of 200 °C gave the highest sample recovery, measured as total peak area while an inlet temperature of 100 °C as well as 280 °C gave the lowest total area values. An increase in desorption time from 3 to 5 min. Resulted in a recovery at 100 °C close to that obtained at 200 °C. Peak broadening was minimal, and only observed at the 100 °C inlet temperature. Based on these results, we highly recommend that SPME users include desorption temperature as one variable when developing sampling procedures for novel biological systems to ensure that potentially present thermally labile compounds are not degraded.