Solid-Phase Microextraction and the Human Fecal VOC Metabolome

Abstract

The diagnostic potential and health implications of volatile organic compounds (VOCs) present in human feces has begun to receive considerable attention. Headspace solid-phase microextraction (SPME) has greatly facilitated the isolation and analysis of VOCs from human feces. Pioneering human fecal VOC metabolomic investigations have utilized a single SPME fiber type for analyte extraction and analysis. However, we hypothesized that the multifarious nature of metabolites present in human feces dictates the use of several diverse SPME fiber coatings for more comprehensive metabolomic coverage. We report here an evaluation of eight different commercially available SPME fibers, in combination with both GC-MS and GC-FID, and identify the 50/30 µm CAR-DVB-PDMS, 85 µm CAR-PDMS, 65 µm DVB-PDMS, 7 µm PDMS, and 60 µm PEG SPME fibers as a minimal set of fibers appropriate for human fecal VOC metabolomics, collectively isolating approximately 90% of the total metabolites obtained when using all eight fibers. We also evaluate the effect of extraction duration on metabolite isolation and illustrate that ex vivo enteric microbial fermentation has no effect on metabolite composition during prolonged extractions if the SPME is performed as described herein.

Alterations in the Porcine Colon Microbiota Induced by the Gastrointestinal Nematode Trichuris suis

“…Changes in fecal VOCs have been associated with gastrointestinal diseases (10,12). A GCMS-based VOC analysis of feces obtained from the proximal colon of the control and infected pig cohorts identified (using a strict Ͼ90% identity to the NIST mass spectral library) 170 core metabolites common to both cohorts, while 29 and 27 metabolites were uniquely detected in the control and infected cohorts, respectively (see Table S5 in the supplemental material).…”

“…All samples were stored at Ϫ80°C until analyzed. A headspace solid-phase microextraction (SPME) of the samples was analyzed essentially as described previously (10). The solid-phase microextraction fiber assembly was manually positioned in the headspace above the sample, and the fiber was exposed to the volatiles for 18 h (the sample vial temperature was held at 60°C for the duration of the exposure).…”

Human intestinal gas measurement systems: in vitro fermentation and gas capsules

“…Current methods of intestinal gas measurement predominantly rely on indirect processes such as breath analysis [7,8]. However, gas analyses of fecal cultures and direct sampling of gas species produced inside the gastrointestinal tract are much more accurate signatures for health assessment and possibly diagnostic use [9][10][11][12][13].…”

“…Fecal samples are easily accessible and provide a good reflection of the metabolic activity of the colonic microbiota, particularly in the distal colon [9][10][11][12][13]. Such experiments involve sampling headspace (gas release) subsequent to incubating fiber substrates with freshly pooled fecal inocula and nutrient medium under conditions mimicking those of the large intestine (at 378C and in complete anaerobic conditions).…”

“…Eventually, the released gas in the headspace is collected either by gas absorption in solid phase microextraction (SPME) fibers or by pumping into the thermal desorption tube. The types and constituents of the collected gas samples are then assessed mainly using gas chromatography coupled with mass spectrometry (GC-MS) [9][10][11][12][13]. The gas sample is first separated through the GC column by the flow of an inert gas.…”