Rapid Analysis of Volatile Flavor Compounds in Apple Fruit Using SPME and GC/Time-of-Flight Mass Spectrometry

Abstract

Solid-phase microextraction (SPME), time-compressed chromatography (TCC), and time-of-flight mass spectrometry (TOFMS) were examined for their suitability and compatibility for rapid sampling, separation, and detection of apple flavor volatiles. Flavor-contributing volatile compounds were found to have relatively high partition coefficients on a 100 μm thick coating of polydimethylsiloxane (PDMS) on a SPME fiber. The time required to saturate the PDMS coating was highly volatile-dependent, varying from less than 2 min to greater than 30 min. However, the response of this system was linear in the ppb to ppm range when the adsorption duration was standardized. The speed of the TOF mass spectrometer permitted identification and quantification of compounds having chromatographic peak widths of only a fraction of a second. The unskewed nature of fragmentation patterns obtained allowed individual component spectral characterization of unknown compounds even when not fully chromatographically separated. Thus, the time required for chromatography could be reduced by an order of magnitude without loss in analytical performance. Typical analysis times for complex mixtures were 2−5 min as compared with 20−60 min required for standard purge-and-trap analyses. Keywords: SPME (solid-phase microextraction); time-compressed chromatography; time-of-flight mass spectrometry; headspace sampling; partition coefficient; purge-and-trap; volatiles; flavor; apples