Full-range analysis of ambient volatile organic compounds by a new trapping method and gas chromatography/mass spectrometry

This study investigated the feasibility of analyzing a full range of ambient volatile organic compounds (VOCs) from C ₃ to C ₁₂ using gas chromatograph mass spectrometry (GC/MS) coupled with thermal desorption. Two columns were used: a PLOT column separated compounds lighter than C ₆ and a DB-1 column separated C ₆-C ₁₂ compounds. An innovative heart-cut technique based on the Deans switch was configured to combine the two column outflows at the ends of the columns before entering the MS. To prevent the resolved peaks from re-converging after combining, two techniques were attempted (hold-up vs. back-flush) to achieve the intended " delayed" elution of heavier components. Thus, the resulting chromatogram covering the full range of VOCs is a combination of two separate elutions, with the heavier section following the lighter section. With the hold-up method, band-broadening inevitably occurred for the delayed C ₆-C ₇ DB-1 compounds while the light compounds eluted from the PLOT column. This broadening problem resulted in peak tailing that was largely alleviated by adding a re-focusing stage while the DB-1 compounds were back-flushed, and this modified technique is referred to as the back-flush method. With this modification, the separation of the C ₆-C ₇ compounds improved dramatically, as revealed by the decrease in peak asymmetry (As) and increase in resolution. Linearity and precision for these peaks also improved, yielding R ² and RSD values better than 0.9990 and 2.8%, respectively.