Solid phase microextraction (SPME) is a well established sampling technique that is often used to isolate volatile organic components in gaseous mixtures.
Solid phase microextraction (SPME) is a well established sampling technique that is often used to isolate volatile organic components in gaseous mixtures. Once the compounds have been collected, the SPME fibers are typically placed into a heated GC inlet which thermally desorbs these components into a GC–MS system for analysis. Normally, this analysis can take between 10–30 min to complete depending on the complexity of the samples. In this work, the Direct Analysis in Real Time (DART™ ) heated gas stream is used to desorb and directly introduce a SPME sample into a high-resolution mass spectrometer. This methodology produces comparable information to the traditional GC–MS technique, but streamlines the results into only a few seconds of analysis time.
A Supelco DVB/Carboxen/PDMS StableFlex SPME fiber was placed in an enclosed plastic bag with a banana for 10 min during each analysis. For direct analysis of the SPME fiber, the JEOL AccuTOF-DART™ system was set to the following parameters: needle voltage 3500V, discharge electrode 150V, grid electrode 250V, helium temperature 200 °C, and helium flowrate 2.3 L/min. A JEOL GC-Mate II high resolution sector bench top system equipped with a DB5-HT (0.25mm × 30m) was used for the GC–MS portion of the analysis. The GC-Mate II was set to the following parameters: inlet temperature 250 °C, split ratio 30, and helium flowrate 1.2 mL/min. The GC oven was set for the following temperature profile: 40 °C held for 2 min, ramp from 40 to 260 °C at 20 °C/min, 260 °C held for 2 min.
Figure 1: AccuTOF-DART mass spectrum for banana fragrances from SPME fiber.
Figure 1 shows a typical AccuTOF-DART™ mass spectrum obtained for a banana headspace sample. At first glance, this spectrum might appear complex, but using the JEOL-provided ChemSW Search from List Software, all of the [M+H]+ , [M+NH4]+ , and [2M+H]+ for each alcohol, acetate, and butyrate were identified, summed together, and normalized in a matter of seconds. Additionally, these results were directly comparable to the data obtained for the traditional GC–MS analysis done using the GC-Mate II. Figure 2 shows a side-by-side comparison of these data sets. This work clearly demonstrates that the AccuTOF-DART™ can be used with SPME to quickly produce results that are comparable to traditional analysis techniques.
Figure 2: Comparison of relative abundances observed for each compound using GCâMS and DART-MS analysis.
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