Db 5 gc ms column

Aliquots (2 µL) of pooled and concentrated web extract (100 webs in 400 µL of solvent) were analysed by GC–MS, using a Varian Saturn Ion trap 2000 (Varian Inc., now Agilent Technologies Inc., Santa Clara, CA 95051, USA) and an Agilent 7890B GC coupled to a 5977 A MSD, both fitted with a DB-5 GC-MS column (30 m × 0.25 mm ID, film thickness 0.25 µm). The injector port was set to 250 °C, the MS source to 230 °C, and the MS quadrupole to 150 °C. Helium was used as a carrier gas at a flow rate of 35 cm s⁻¹, with the following temperature programme: 50 °C held for 5 min, 10 °C min⁻¹ to 280 °C (held for 10 min). Compounds were identified by comparing their mass spectra and retention indices (relative to aliphatic alkanes^{67 (link)}) with those of authentic standards that were purchased or synthesised in our laboratory (Supplementary Table 1).

We collected (commonly discoloured) droplets of honeydew from plants heavily infested with pea aphids, using a 10-µL glass capillary fitted with a rubber bulb. We collected a total of 50 µL of honeydew and expelled it into a 4-mL glass vial with a rubber septum lid. Through this lid, we inserted a carboxen-polydimethylsiloxene-coated solid-phase micro extraction (SPME) fibre (75 µm; Supelco Inc., Bellefonte, PA, USA), allowing absorption of honeydew odorants on this fibre for 24 h at room temperature. Prior to each odorant collection, we conditioned the fibre at 280 °C for 5 min in a gas chromatograph (GC) injection port. We desorbed odorants from the fibre in the hot (250 °C) injection port of the GC, and analyzed odorants by GC-mass spectrometry (MS) using a Saturn 2000 Ion Trap GC-MS fitted with a DB-5 GC-MS column (30 m × 0.25 mm i.d.; Agilent Technologies Inc., Santa Clara, CA, USA) in full-scan electron impact mode. We used a flow of helium (35 cm s⁻¹) as the carrier gas with the following temperature program: 40 °C (5 min), 10 °C min⁻¹ to 280 °C (held for 10 min). We identified volatiles by comparing their retention indices (RI) relative to n-alkane standards [47 (link)] and their mass spectra with those reported in the literature [48 ] and with those of authentic standards.

After adding octyl acetate as an internal standard to HSV extract, we analyzed 2-µl aliquots by gas chromatography-mass spectrometry (GC-MS), operating a Saturn 2000 Ion Trap GC-MS fitted with a DB-5 GC-MS column (30 m × 0.25 mm i.d.; Agilent Technologies Inc., Santa Clara, CA 95051, USA) in full-scan electron impact mode. We used a flow of helium (35 cm s⁻¹) as the carrier gas with the following temperature program: 50 °C (5 min), 10 °C min⁻¹ to 280 °C (held for 10 min). The temperature of both the injector port and ion trap was 250 °C. To reveal the presence of low-molecular-weight carboxylic acids (which chromatograph poorly), we converted carboxylic acids to the corresponding silylated derivatives (which chromatograph well). To this end, we treated a 100-µL aliquot of HSV extract with BSTFA (10 µl; N,O-bis(trimethylsilyl)trifluoroacetamide) and TMCS (10%; trimethylchlorosilane; both Pierce Chemical Co., Rockford, IL 61101, USA) and after 5 min without any work-up analyzed 2-µl aliquots by GC-MS. We identified odorants in HSV extract by comparing their retention indices (RI; relative to n-alkane standards^{65 (link)}) and their mass spectra with those reported in the literature⁶⁶ and with those of authentic standards (Table 1).