Rxi 624sil column

For GC-MS analysis, separate aliquots of 5 ml are taken from each sample to run through a Bruker Scion SQ GC-MS instrument. Each aliquot was agitated and heated to 60°C for 5 minutes, before the contents of its headspace are extracted using a Combi-PAL ITEX automated pre-concentrator system. The volatiles contained in the ITEX were then released by heating to 250°C, and injected into the instrument at a split ratio of 1∶20 with helium carrier gas. The Restek Rxi-624Sil column (20 m length, 0.18 mm ID, 1.0 um df) fitted to the GC was kept at a constant 50°C for 1 minute before being increased up to 280°C at a rate of 20°C/min, separating out the constituent VOCs in terms of molecular weight and polarity. After an initial detection to produce a chromatogram, the VOC molecules are fragmented by the mass spectrometer and detected to produce corresponding mass spectra. These are correlated with the GC chromatogram peaks, and checked against a National Institute of Standards and Technology library (NIST 2013) of chemical compounds. This was perfrimed in order to gain additional insight into the specific chemical groups that make up the volatile headspace of the urine samples in those with CRC.

1 mL of each post-fermentation media sample was combined with 200 µL of 5 M NaCl prior to analysis. Standard solutions of ethanol, acetaldehyde, formaldehyde, and methanol were made to the same volume and NaCl concentration. Gas chromatography (GC) headspace analysis was performed using a Clarus 600 with a Turbomatrix 110 Headspace sampler (PerkinElmer). Headspace sampling was performed with an oven temperature of 70 °C, injection time of 0.04 min, and column pressure of 16 psi, Samples were separated using a Restek Rxi-624Sil Column (30 m length, 0.32 mm ID) with He as a carrier gas at 2.5 mL/min at 90 °C, and a GC cycle time of 3.2 min.