Thermal instability of germacrone: implications for gas chromatographic analysis of thermally unstable analytes

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Abstract
The rearrangement of germacrone (1) to β-elemenone (2) is common during gas chromatographic (GC) analysis, with the conversion taking place in the injector port at temperatures above 250 °C as well as on the column. While production of 2 in the injector is evident from the gas chromatographic trace, 2 produced from 1 during its migration down the column is difficult to detect because of the diffuse nature of the chromatographic peak produced by this process. A mathematical model and kinetic parameters (A = (1.35 ± 0.03) × 10−3s−1; Ea = 137 ± 4 kJ mol−1) determined from the reaction in solution can be used to estimate the degree of conversion of 1 to 2 for chromatographic runs (including temperature-programmed analyses). The results of these calculations verify that substantial amounts of 1 are converted to 2 under conditions that are commonly used for the analysis. The method for modeling thermally induced rearrangements in nonisothermal processes represents the first approach to quantitatively assessing their importance in GC analyses of thermally labile substances. Keywords: kinetics, gas chromatography, thermal rearrangement, germacrone, β-elemenone.

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