| MS Description
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Sample preparation procedure<br />&l … Sample preparation procedure<br /><br />
The samples were crushed into powder (2 min at 4 °C) in a Mixer Mill MM 311 instrument featuring a grinding jar with a stainless steel screw cap (Restech, Tokyo, Japan) and the frozen powder from each sample (flesh weight, 1 g) was weighed in a 20-ml HS vial (Supelco, MO, USA). For VOC profiling of Allium plants we used a modified method of Tikunov et al. and Kusano et al. Briefly, the 20-ml HS-GC vial (Supelco) containing the frozen powder was closed with a magnetic screw cap (AMR, Tokyo, Japan) for ITEX- and SPME-analysis. Then, 1 ml of 100 mM 2,2′,2′’,2′’’-(ethane-1,2-diyldinitrilo) tetraacetic acid (EDTA)- NaOH water solution (pH 7.5) was added to each vial; the water derived from an Allium sample was considered to be equal to 1 ml. After vortexing, 10 μl of solution containing n-decane (d 22 , 99 %; 50 μM), n-pentadecane (d 32 , 98 %; 50 μM), n-eicosane (d 42 , 98 %; 50 μM) for definition of RI and EPA524.2 fortification solution (20 μg/ml of fluorobenzene, 4-bromofluorobenzene, and 1,2-dichlorobenzene-d4) as ISs was mixed in methanol, then solution was added to each vial as IS. Solid CaCl2 was added to obtain a final concentration of 5 M and the samples were stored overnight at 22 °C.<br />
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HS collection using the SPME fiber<br />
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The SPME device for a CTC CombiPAL auto-sampler (CTC Analytics, Zwingen, Switzerland) was purchased from AMR (Tokyo, Japan). We used an SPME fiber comprised of a 65-μm-thick layer of polydimethylsiloxane (PDMS)/divinylbenzene (DVB)-fused silica (FS) fiber/stainless-steel (SS) tube. Before analysis, the fiber was conditioned at 250 °C for 30 s in the injection port of an Agilent 6890 N gas chromatograph (Agilent Technologies, Wilmington, USA) equipped with a 30 m × 0.25 mm inner diameter fused-silica capillary column with a chemically bound 0.25-μl film Rtx-5 Sil MS stationary phase (RESTEK, Bellefonte, USA). Collection of volatiles was carried out by inserting the SPME-fiber to the vial and by trapping the VOCs for 20 min at 80 °C under continuous agitation. After HS collection it was placed in the injection port of the gas chromatograph that was coupled to a Pegasus III TOF mass spectrometer (LECO, St. Joseph, USA). The thermodesorption of VOCs occurred for 15 s at 250 °C.<br />
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HS collection using the ITEX device<br />
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We used a CTC CombiPAL auto-sampler (PAL COMBI-xt) featuring the ITEX device PAL ITEX-2 option (CTC Analytics). The ITEX procedure was controlled with a PAL Cycle Composer (CTC analytics). We conducted preliminary experiments to choose an appropriate sorbent material from the four materials, Tenax TA, Tenax GR (TGR), Carbosieve SIII (CSIII) and mixed TGR and CSIII (TGR/CSIII), that are commercially available (data not shown). Then, we chose that the sorbent material for the ITEX-2 portion was TGR (80/100 mesh)/CSIII (60/80 mesh). The parameters for HS collection were as described in the Additional file 2. After HS collection, 500 μl of the HS sample were injected into the injection port of the gas chromatograph coupled to the mass spectrometer used for HS collection by ITEX.<br />
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GC-TOF–MS analysis<br />
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GC-TOF–MS conditions were as described in the Additional file 2. Data acquisition was on a Pegasus III TOF mass spectrometer (LECO); the acquisition rate was 30 spectra/s in the mass range of a mass-to-charge ratio of m/z = 30–550. Five ISs were used for data normalization.<br /> e used for data normalization.<br />
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