Analysis of Alkaline and Neutral Volatile Metabolites in Feces by Gas Chromatography-Tandem Mass Spectrometry

A rapid gas chromatography-tandem mass spectrometric (GC-MS) method was developed for the analysis of alkaline and neutral volatile metabolites of feces from human and rats. Feces were extracted by 75% methanol solution (V/V). After addition of ammonia solution (pH 10, final concentration of 1%), the supernatant was subjected to GC-MS analysis. The interesting compounds were separated on a CP-Sil 5 (25 m × 0.25 mm × 0.12 μm) capillary column. Helium was employed as a carrier gas at a constant flow rate of 1 mL min−1. Oven temperature was programmed as follows: the initial temperature was set at 50 °C and held for 1 min, then increased at 25 °C min−1to 150 °C, sustained for 1 min; increased at 20 °C min−1to 200 °C, held for 2 min; and finally increased at 10 °C min−1to 270 °C, maintained for 5 min. The MS was operated in the electron impact ionization mode at −70 eV. The injector, ion source and transfer line temperatures were maintained at 220 °C, 230 °C and 280 °C, respectively. Mass data were acquired in full scan mode of m/z10–600. The solvent delay time was set 3 min. A total of eleven volatile components were identified in the feces samples from human and seven in the feces samples from rats by retrieving the NIST library, comparing with the standards and analyzing the MS data. The method was simple and sensitive, and could be used to detect alkaline and neutral volatile metabolites of feces from human and rats.